BEHIN POULAD INDUSTRIAL GROUP CO.

ASM Handbook, Volume 14A: Metalworking: Bulk Forming Copyright © 2005 ASM International®S.L. Semiatin, editor, p383-404 All rights reserved.DOI: 10.1361/asmhba0004004 www.asminternational.orgCold HeadingRevised by Toby Padfield, ZF Sachs Automotive, and Murali Bhupatiraju, Metaldyne Corporation COLD HEADING is a forming process of Figure 1 illustrates the process of cold heading half times the blank diameter can be upset in oneincreasing the cross-sectional area of a blank, of a blank. Figure 2 shows the sequence of steps blow (Fig. 3a).which is at room temperature, at one or more in the production of a screw blank in three blows.points along its length. The material flow over Advantages of the process over machining of the A cone-shaped cavity in the heading toolthe length where the cross-sectional area same parts from bar stock include: (punch) also can be used to upset a length ofincreases and the length decreases is identical to more than two-and-a-half times the blank dia-conventional upsetting. Along with the upsetting  Almost no waste material meter in one blow (Fig. 3b). If the buckle point ofprocess, cold-headed parts may also undergo  Increased strength from cold working the blank cannot be contained within a cone-other processes, such as extrusion, coining,  Controlled grain flow shaped heading tool (punch), a sliding cone-trimming, hole punching, and thread rolling.  Higher production rate shaped die cavity has to be used to support the blank (Fig. 3c). Otherwise, multiple blows are Cold-heading is typically a high-speed pro- Process Parameters in Cold Heading required to upset more than two-and-a-half dia-cess where the blank is progressively moved meters. Lengths up to four-and-a-half diametersthrough a multi-station machine. The process is Upset Length Ratio. The ratio of initial can be upset with two blows (ratio=4.5).widely used to produce a variety of small- and length being upset to the initial diameter of the Lengths up to eight diameters can be upset withmedium-sized hardware items, such as screws, blank is called the upset length ratio. The upsetbolts, nuts, rivets, and specialized fasteners. Cold length ratio determines the number of blows and 0.174 diam 1022 steelheading is used to produce automotive compo- the form of the upset required to prevent buck- 0.173 Ejectornents, such as gear blanks, ball studs, piston pins, ling. Unsupported lengths of up to two to two-sparkplug shells, valve spring retainers, engine and-a-half times the blank diameter can be upset 1.310poppet valves (intake and exhaust), and trans- in one blow (ratio=2 to 2.5) in steel and up to Slugmission shafts. The bearing industry uses cold four diameters (ratio=4) for copper (Ref 1). Byheading to manufacture inner and outer races as enclosing the blank in a die cavity of one-half Punchwell as precision balls and cylindrical rollers. times the blank diameter, more than two-and-a-Advancements in cold-heading machines allowparts to be formed that are longer than 300 mm(12 in.) and greater than 3 kg (7 lb) in mass. Die First blow Punch Ejector body Insert Second blow Die Ejector Ejector PunchPunch Part Die(a) (b) Reheading and pointing Die 0.345 min 0.206 diam 0.200 0.414 diam 0.384 0.161 diam 0.159 0.031 0.220 (c) (d) 0.019 0.148 0.210Fig. 1 Schematics of the cold heading of an unsupported bar in a horizontal machine. (a) Head formed between punch 0.130 0.865 0.845 and die. (b) Head formed in punch. (c) Head formed in die. (d) Head formed in punch and die Completed workpiece Fig. 2 Cold heading of a screw blank in three blows

384 / Cold Heading and Cold Extrusionthree blows (ratio=8.0). Again, punches and  Bottom thickness during backward extrusion headed. These metals and alloys are sometimesdies can be designed to increase the upset should not be less than 1 to 1.5 · the extruded warm headed (see the section “Warm Heading”lengths. For example, using a cone-shaped wall thickness. in this article).heading cavity, lengths of up to six diameters canbe upset in two blows (upset ratio=6.0).  Open forward extrusions should be a max- Carbon and Alloy Steels. Steels containing imum of 25% reduction for aluminum, 35% up to approximately 0.20% C are the easiest to Upset Diameter Ratio. The ratio of final for carbon steels, and 40% for alloy steel such cold head. Medium-carbon steels containing upupset diameter to the initial blank diameter is as 4140. Trapped forward extrusion can have to 0.40 to 0.45% C are fairly easy to cold work,called the upset diameter ratio. The upset dia- reductions as high as 70 to 75%. but formability decreases with increasing carbonmeter ratio limit is sensitive to the type of and manganese content. Alloy steels with morematerial, material condition, lubrication, and  Multiple forward extrusion should have the than 0.45% C, as well as some grades of stainlessshape of the upset. Finished diameters from two highest reduction first, due to the removal of steel, are very difficult to cold head and result intimes blank diameter to two-and-a-half times lubricants and coatings that impair subsequent shorter tool life than that obtained when headingblank diameter can be achieved (ratio=2.0 to forming. The number of extrusions over the low-carbon steels. Tables 1 and 2 list some2.5). Larger diameters (ratio j3.0) can be same axial portion should be limited to three. common grades and their relative formability.achieved in closed-die upsetting and upsetting of More information about chemical compositionsshapes such as carriage bolts.  Double forward extrusion should be limited to and other properties of cold-heading steels can a maximum reduction of 30%, and the dis- be found in appropriate industry standards Upset Strain. The upset strain is the true tance between extrusions should be at least (Ref 21–30).strain in the material, expressed as strain=ln one blank diameter.(l0/l1). An upset strain limit of 1.6 is commonly Cold-heading-quality steels are subject to millused as a rule of thumb. Spheroidize annealing  It is preferred to upset before open extrusion, testing and inspection designed to ensure internalheat treatment of blanks is commonly used to unless there is a need to extrude the diameter soundness, uniformity of chemical composition,increase the upset strain limit beyond 1.6. immediately under the head. and freedom from detrimental surface imper- fections. Most cold-heading-quality alloy steels The cold heading process limits are sensitive More information on specific case studies can be are low- and medium-carbon grades. Typicalto the type of material, material condition, found in Ref 11 to 13. low-carbon alloy steel parts made by coldlubrication, equipment, and shape of the upset. heading include fasteners (cap screws, bolts,Therefore, the limits discussed in this section The use of computers and simulation software eyebolts), studs, anchor pins, and rollers forshould be considered as general recommenda- for modeling cold-heading processes has bearings. Examples of medium-carbon alloytions and not as definitive rules. References 2 to 5 increased to the point where they are used daily. steel cold-headed parts are bolts, studs, andprovide additional information on the process Simulations are used to develop forming hexagon-headed cap screws. Special cold-head-parameters for upsetting. progressions, analyze tooling stresses, and pre- ing-quality steels are produced by closely con- dict stresses and damage in the workpiece trolled steelmaking practices to provide uniform Process Sequence Design. The design of (Ref 14–19). More information on these tech- chemical composition and internal soundness.forming process sequences has historically been niques can be found in the Section “Modeling Also, special processing (such as grinding) isachieved by a combination of empirical and and Computer-Aided Process Design for Bulk applied at intermediate stages to remove detri-calculation methods. Skilled designers, using Forming” in this Volume. mental surface imperfections. Typical applica-creativity, intuition, and experience, have cre- tions of alloy steel bars of this quality are frontated most of the guidelines for forming sequence Materials for Cold Heading suspension studs, socket screws, and somedesign. The following guidelines can be used for valves.combining upsetting with extrusion operations, Cold heading is most commonly performed onas well as for combining forward-backward low-carbon steels having hardnesses of 60 to 87 Table 1 Cold formability of carbon steelsextrusion and multiple extrusion operations HRB. Copper, aluminum, stainless steels, and(Ref 6–10): some nickel alloys can also be cold headed. Best Good Fair Poor Other nonferrous metals and alloys, such as Backward extrusions should have a minimum titanium, beryllium, magnesium, and the 1008 1018 1035 1045 reduction of 20 to 25% and a maximum of 70 refractory metals and alloys, are less formable at 1010 1020 1038 1050 to 75%. room temperature and may crack when cold 1013 1022 1040 1060 1016 1024 ... 1070 1.5 D Punch 1017 1030 ... 1080 max Punch Note: Grades within each column are listed in numerical order and do not indicate a formability rank within the column. The physical and Sliding mechanical properties resulting from variable processing of the material cone selected may influence its rank. The ranking will also be influenced by the type of cold forming to be done, wire coating, and lubricants used. Source: Ref 20L Ͼ 2.25D Table 2 Cold formability of alloy steels(a) (b) (c) Best Good Fair PoorFig. 3 Die designs to overcome buckling of the blank. (a) Enclosed upset. (b) Cone-shaped cavity punch. (c) Sliding 3115 3120 1522 1340 5015 3130 2330 1541 cone-shaped cavity die 5115 4037 3140 4340 ... 5120 4130 4640 ... 8620 4140 6150 ... 8720 5140 52100 ... 8640 ... ... 8740 ... ... ... Source: Ref 20

Cold Heading / 385 Cold-heading-quality alloy steel rod is used of the finishing draft are to provide a lubricating depending on their hardness and yield strength infor the manufacture of wire for cold heading. coating that will aid the cold-heading operation the annealed condition. Stock sizes in excess ofSevere cold-heading-quality rod, for single-step and to produce a kink-free wire coil having more these limits are normally hot formed.or multiple-step cold forming where inter- uniform dimensions.mediate heat treatment and inspection are not Cold-heading equipment requires wire rodpossible, is produced with carefully controlled Cold-heading wire is produced with a variety with diameter tolerances in the range of 0.076 tomanufacturing practices and rigid inspection of finishes, all of which have the function of 0.127 mm (0.003 to 0.005 in.). Because alloypractices to ensure the required degree of internal providing proper lubrication in the header dies. 400 should be cold headed in the 0 or No. 1soundness and freedom from surface imperfec- The finish or coating should be suitably adherent temper to provide resistance to crushing andtions. A fully killed fine-grained steel is usually to prevent galling and excessively rapid die wear. buckling during forming, these tolerances canrequired for the most difficult operations. Nor- A copper coating, which is applied after the normally be obtained with the drawing pass usedmally, the wire made from this quality rod is annealing treatment and just prior to the finishing to develop this temper. For tighter tolerances orspheroidize annealed, either in process or after draft, is available; the copper-coated wire is then harder alloys, fully cold-drawn material must bedrawing finished sizes. lime coated and drawn, using soap as the drawing used. lubricant. Coatings of lime and soap or of oxide Dual-phase steels featuring ferrite-martensite and soap are also employed. The surface quality of regular hot-rolled wireor ferrite-pearlite microstructures have been rod, even with a cold sizing pass, may not bedeveloped specifically for cold-heading appli- Table 3 lists some common grades and their adequate for cold heading. Consequently, acations, especially for high-strength fasteners relative formability. More information on chem- special cold-heading-quality wire rod is usuallythat do not require subsequent quench and tem- ical compositions and other properties can be recommended. Configurations that are especiallyper treatments to attain mechanical property found in consensus standards (Ref 36–38). susceptible to splitting, such as rivets, flat-headrequirements (Ref 31–35). These steels obtain Table 3 also includes some specialty alloys based screws, and sockethead bolts, require shaved ortheir strength from a combination of thermo- on iron, nickel, or cobalt. These are used when centerless-ground material. If cold-headed partsmechanical processing at the steel mill and strain conventional steels and stainless steels do not are to be used for high-temperature service, ahardening during wire drawing and cold heading. provide sufficient strength, corrosion resistance, postwork heat treatment may be needed.The strength of these alloys can be increased or elevated-temperature properties (creep, oxi-further by strain aging that occurs during low- dation, etc.). A common grade includes A-286 Lubrication. To prevent galling, high-gradetemperature heating after forming. The elevated (UNS K66286), an iron-base precipitation- lubricants must be used in cold heading of nickelstrength and work hardening of these alloys hardening alloy; alloy 718 (UNS N00718) is a alloys. Lime and soap are usually used as a baseresult in higher forming loads and therefore can precipitation-hardenable nickel-base superalloy. coating on alloy 400. Better finish and die lifeaffect tool life. These alloys are all very difficult to cold head, can be obtained by using copper plating 7.5 to and warm- and hot-heading techniques often are 18 mm (0.3 to 0.7 mils) thick as a lubricant car- Stainless Steels and Specialty Alloys. Some used to improve the formability. rier. Copper plating also may be used on thestainless steels, such as the austenitic types 302, chromium-containing alloys 600 and 800, but304, 305, 316, and 321 and the ferritic and Titanium Alloys. Some titanium alloys, such oxalate coatings serve as an adequate substitute.martensitic types 410, 430, and 431, can be cold as the Russian alpha-beta alloy VT16 (Ti-5Mo-headed. Precipitation-hardening alloys provide 5V-2.5Al) and the metastable beta alloy Ti-3Al- Regardless of the type of carrier, a basehigher strength levels than conventional stainless 8V-6Cr-4Mo-4Zr (Beta C, UNS R58640), can be lubricant is best applied by drawing it on in asteels, but the higher initial strength decreases successfully cold headed (Ref 39–41). Ti-6Al- light sizing pass to obtain a dry film of theheadability. All stainless steels work harden 4V (UNS R56400) is an alpha-beta titanium lubricant. Any of the dry soap powders of themore rapidly than carbon steels and are therefore alloy with high strength in the annealed condi- sodium, calcium, or aluminum stearate types canmore difficult to cold head. More power is tion, which can be further increased with heat be applied this way.required, and cracking of the upset portion of the treating. This alloy may be difficult to cold head,work metal is more likely than with carbon or and warm- or hot-heading methods may be If the wire rod is to be given a sizing or tem-low-alloy steels. These problems can be alle- needed to improve workability. pering pass before the cold-heading operations,viated by preheating the work metal (see the the heading lubricant should be applied duringsection “Warm Heading” in this article). Cold Heading of Nickel Alloys. The high drawing. strength and galling characteristics of nickel Cold-heading wire is produced in any of the alloys require slow operating speeds and high- Lubrication for cold heading is completed byvarious types of stainless steel. In all instances, alloy die materials. Cold-heading machines dripping a heavy, sulfurized mineral oil or acold-heading wire is subjected to special testing should be operated at a ram speed of approxi- sulfurized and chlorinated paraffin on the blankand inspection to ensure satisfactory perfor- mately 10 to 15 m/min (35 to 50 ft/min). These as it passes through the heading stations. Prior tomance in cold-heading and cold-forging opera- ram speeds correspond to operating speeds of 60 heat treatment or service, the parts must betions. to 100 strokes/min on medium-sized equipment. thoroughly cleaned to ensure that all lubricant Because of the high strength and work-hardening has been removed. Of the chromium-nickel group, types 305 and rates of the nickel alloys, the power required for302Cu are used for cold-heading wire and gen- cold forming may be 30 to 50% higher than that Copper and Aluminum Alloys. Copper anderally are necessary for severe upsetting. Other required for mild steels. Tools should be made of aluminum alloys are the easiest metals to coldgrades commonly cold formed include 304, 316, oil-hardening or air-hardening die steel. The air-321, 347, and 384. hardening types, such as AISI D2, D4, or high- Table 3 Cold formability of stainless steels speed steel (M2 or T1), tempered to 60 to 63 and specialty alloys Of the 4xx series, types 410, 420, 430, and 431 HRC, are preferred.are used for a variety of cold-headed products. Best Good Fair PoorTypes 430 and 410 are commonly used for Rod stock (usually less than 25 mm, or 1 in.,severe upsetting and for recess-head screws and in diameter) in coils is used for starting material, 410 305 304 301bolts. Types 416, 416Se, 430F, and 430FSe are because cold heading is done on high-speed 430 302HQ 316 303intended primarily for free cutting and are not automatic or semiautomatic equipment. 384 . . . 321 309recommended for cold heading. Although alloy 400 is sometimes cold headed in ... ... 420 310 larger sizes, 22 mm (7/8 in.) is the maximum ... ... 431 347 Cold-heading wire is manufactured using a diameter in which alloys 400 and K-500 can be ... ... A-286 416closely controlled annealing treatment that pro- cold headed by most equipment. Limiting sizes ... ... ... PH stainless gradesduces optimal softness and still permits a very in harder alloys are proportionately smaller, ... ... ... Alloy 718light finishing draft after pickling. The purposes ... ... ... Greek Ascoloy ... ... ... Waspaloy PH, precipitation hardening. Source: Ref 20

386 / Cold Heading and Cold ExtrusionTable 4 Cold formability of copper and Purpose Materials, Volume 2, ASM Handbook, reduced to 1/3 of its initial value without crackingcopper alloys 1990, and in Ref 43 to 46. (Ref 23, 47).Best Good Fair Workability and Defects Scrapless nut wire is used in the most severe forming operations, where both upsetting andC10200 (OFHC) C15000 C14500 Metal formability is affected by the chemical backward extrusion are required. Low- andC11000 (ETP) C16200 C14700 composition; microstructure; surface condition, medium-low-carbon direct-drawn wire or wireC11400 C17200 C28000 including coatings and/or lubricants; and the drawn from annealed rods is used for non-heat presence of internal defects. Issues that pertain to treated nuts (property classes 4 to 8, ISO 898-2),C12200 C18200 (Muntz metal) all metals include chemical segregation, varia- depending on the severity of deformation.C22000 C18700 C35000 bility in grain size/aspect ratio, presence of other Medium-carbon wire used for heat treated nutsC23000 C27400 C35300 phases, texture (preferred orientation), and sur- (property class 9 or 10) is normally drawn from C35600 face defects such as seams, laps, pits, voids, sliv- annealed or spheroidize-annealed bars or rods or (red brass) (yellow brass) ers, scratches, and rolled-in scale or oxides. is produced AIP.C24000 C31400 C61400C26000 C33000 C63000 Carbon and alloy steel grades are generally Tubular rivet wire has similar requirements categorized in the following application varia- for both heading and extruding but is usually (cartridge brass) C54400 ... tions: cold heading, recessed head, socket head, supplied from low-carbon aluminum-killed steelC42500 C69700 ... scrapless nut, and tubular rivet (Ref 21). These in the SAIP condition, where the final drawingC44300 C70600 ... wire variations are produced to meet specific reduction is somewhat heavier than normal. ThisC50200 C71000 ... requirements for chemical composition, me- heavy draft strengthens the wire in order to pre-C51000 C71500 ... chanical properties, surface quality, and internal vent buckling of the shank during the extrusionC52100 C77000 ... soundness. Table 6 shows the maximum allow- operation. The SAFS wire also can be used, withC52400 ... able residual element limits as well as the the final drawing reduction in front of the header.C65100 ... ... restricted levels for phosphorus and sulfurC65500 ... ... required for cold heading steel in order to pro- Formability Considerations for Steels.C68700 ... ... vide optimal formability and tool life. Surface When steel is ordered spheroidized according toC75200 ... ... defects are required to be less than 75 mm ASTM F 2282, the requirement is a minimumC76200 ... (0.003 in.) or 0.5D (finished wire diameter), rating of G2 or L2 (~60% spheroidized, with whichever is greater. Ferrite decarburization is some lamellar carbides and grain boundaries stillNote: OFHC, oxygen-free high conductivity; ETP, electrolytic tough limited to 25 mm (0.001 in.), with partial dec- present). This is really only suitable for lightpitch. Source: Ref 20 arburization (total average affected depth) limits heading and not for operations requiring heavy between 130 and 250 mm (0.005 and 0.010 in.) upsetting or extrusion. The carbide aspect ratio atTable 5 Cold formability of and worst-location depths between 200 and this amount of spheroidization is still as high as 8aluminum alloys 380 mm (0.008 and 0.015 in.). to 15 (Ref 48). Improved formability, suitable for recessed-head or socket-head wire, is obtainedBest Good Fair Cold-heading wire that has been direct drawn when spheroidization is 490%, with an aspect from low-carbon steel wire rods can be used ratio predominantly below 5. Optimal perfor-1100-O 2017-H13 2117-T4 for simple two-blow upsets or for standard mance is obtained when the carbides are uni-1100-H14 2024-H13 6056-T6 trimmed hexagon-head cap screws, but more formly distributed and have an aspect ratio of 1 to2017-O 2117-H15 6061-T6 demanding applications require a suitably an- 2 (Ref 49–52).2024-O 3003-H32 7075-H13 nealed microstructure for optimal workability.2117-O 5056-H32 Annealed-in-process (AIP) or spheroidize Other important considerations for maximiz-3003-O 6053-H13 ... annealed-in-process (SAIP) wire is produced by ing the cold formability of steels include silicon5052-O 6061-H13 ... drawing rods or bars to wire, followed by thermal and oxygen concentrations, nonmetallic inclu-5056-O 6063-T5 ... treatment, cleaning and coating, and then a final sions, grain size, and banding/orientation. Sili-6053-O 6063-T6 ... drawing operation. con is a ferrite strengthener and therefore6061-O ... increases flow stress. Silicon content should be6063-O ... ... Recessed-head wire is used in forming fas- 0.20% maximum and 0.10% for unalloyed steels.7075-O ... ... teners with features such as crossed or square Oxygen promotes the formation of nonmetallic ... ... recesses. Improved-surface-quality billets and inclusions, but it is not as detrimental to fracture rods are used to provide better formability. This ductility as sulfur, because the oxides present inNote: Information on temper designations can be obtained from Ref 42. type of wire is generally produced as SAIP or aluminum-killed steels tend to be globular andSource: Ref 20 spheroidize annealed at finish size (SAFS), not long stringers, such as MnS. Sulfur levels which consists of spheroidize annealing after should be maintained below 0.010% for reces-Table 6 Residual and impurity final cold reduction. The SAFS is the most duc- sed-head and socket-head applications andelement limits tile condition and must be finally drawn in front below 0.006% for scrapless nut grades. Inclusion of the header before forming. sizes greater than 10 mm (0.4 in.) impair ducti-Element Maximum concentration, lity, especially when AlN particles are present. mass % Socket-head wire is similar to recessed-head Grain size number, according to ASTM E 112, wire but has superior formability needed for should be greater than 5. Banding of ferrite-Copper 0.20 extruding deep internal hexagon or Torx fea- pearlite structures (not spheroidize annealed)Nickel 0.10 tures. Upsetting tests are usually specified when contributes to excessive variability in flow stressChromium 0.10 applications require consistent workability, and fracture strain and should be maintainedMolybdenum 0.04 along with 100% nondestructive eddy current below 50 mm (0.002 in.) in width. More in-Tin 0.02 inspection. The upsetting test uses a testpiece formation on cold-head quality and defects inNitrogen 0.009 with end sections flat and parallel to each other steels can be found in Ref 49 and 53 to 56.Boron 0.0007(a) and with an initial length (height) h=1.5d, whereSulfur 0.020 d is the testpiece diameter. During the test, Thermomechanical processing (TMP) canPhosphorus 0.020 the length (height) of the test-piece shall be enhance formability by producing a more homo- geneous distribution and finer ferritic grain size(a) Not applicable to boron steels. Titanium shall not exceed 0.01% for at lower hot rolling temperatures (Ref 57–59).steels that do not have an intentional addition of boron and titanium.Source: Ref 21head. Tables 4 and 5 list some common gradesand their relative formability. More informationabout chemical compositions and mechanicalproperties can be found in Properties andSelection: Nonferrous Alloys and Special-

Cold Heading / 387Lower strength and improved ductility are Typical CWF values for type 302 are 122 to 139, defect when heading alloys with low formabilityobtained in medium-carbon unalloyed and and 89 for type 305. Typical Md30 temperature at high strain rates and low temperatures. Morealloyed steels due to the elimination of bainitic for 302 is À 8 to 6 C (18 to 43 F), with type information on workability and testing is avail-and martensitic phases and because of the higher 305 being, À 41 C (À 42 F). able in the article “Evaluation of Workability forferrite-phase fraction. Heading can be performed Bulk Forming Processes” in this Volume and inon as-rolled rods due to the improved deforma- Aluminum alloy workability can be influ- Ref 62 to 64.tion characteristics, or TMP wire can be spher- enced by excessive grain growth, high soluteoidized in shorter process cycles due to the levels, coarse precipitate particles, high-tem- Cold-Heading Machinesimproved annealing response. perature oxidation, and partial eutectic melting (Ref 61). Excessive grain growth can lead to an Cold heading is done on horizontal mechan- Workability of stainless steels can be char- “orange-peel” surface effect or a reduction in ical presses sometimes called headers. Multi-acterized by the cold work-hardening factor mechanical properties. High solute levels station headers with automatic transfer of(CWH) and the Md30 factor (Ref 60). The CWH increase the material strength and therefore the workpiece between stations are called transferfactor varies between 80 and ~150 and is indi- flow stress. Coarse precipitates, high-tempera- headers or progressive headers. Bolt makers, nutcative of the strain-hardening behavior (higher ture oxidation, and eutectic melting are all sig- formers, and parts formers are specialized typesnumbers strain harden more). The Md30 factor is nificant microstructural anomalies and should of transfer headers. Most cold-heading machinesthe temperature (inC) at which 0.3 true strain, or not be present in cold-heading-quality wire. used in high production are fed by coiled wireapproximately 25% area reduction, leads to the stock.transformation of 50% of the austenite to defor- Defects in formed parts include folds,mation martensite. A higher Md30 temperature bursts, adiabatic shear bands, flow localization, In the conventional method, stock is fed intodenotes greater martensite formation during and many different types of cracks. Figure 4(a) the machine by feed rolls and passes through adeformation and therefore higher strain hard- shows an example of proper grain flow after stationary cutoff quill. In front of the quill is aening and reduced cold formability. The Md30 forming through the important underhead fillet shear-and-transfer mechanism. When the wiretemperature can be calculated from the following region of a fastener, while Fig. 4(b) displays a passes through the quill, the end butts against aequation: fold in the same area. Another example of a wire stop or stock gage to determine the length of defect produced during cold/warm heading the blank to be headed. The shear actuates to cutMd30 ¼ 551 À 462ðC þ NÞ À 9:2Si À 8:1Mn appears in Fig. 5, in this case, an internal shear the blank. The blank then is pushed out of the À 13:7Cr À 20ðNi þ CuÞ À 18:5Mo crack. Adiabatic shear bands (Fig. 6) are a typical shear into the transfer, which positions the blank À 68Nb À 1:42ðASTM grain size À 8Þ in front of the heading die. A newer technique Fig. 5 Example of an internal shear crack in the head of consists of a linear feed mechanism (Fig. 7) that grips and ungrips the wire surface while reci- a Ti-6Al-4V fastener produced during warm procating on guide shafts. The large clamping heading. Etchant: 85 mL H2O, 10 mL HF, and 5 mL surface of the grippers minimizes damage to the HNO3. Courtesy of F. Hogue, Hogue Metallography wire surface/coating, especially when working with soft materials such as aluminum. The heading punch moves forward and pushes the slug into the die; at the same time, the transfer mechanism releases the slug and moves back into position for another slug. In the die, the slug is stopped by the ejector pin, which acts as a backstop and positions the slug with the correct amount protruding for heading. The heading operation is completed in this die, and the ejector pin advances to eject the finished piece. In a cold- heading machine with progressive dies, the transfer mechanism has fingers in front of each ofFig. 4 Examples of grain flow in the underhead fillet Fig. 6 Example of adiabatic shear band in the head of a Fig. 7 Linear feed mechanism for wire input to forming region of headed fasteners. (a) Uniform grain Custom Age 625 Plus (UNS N07716) fastener machine. Courtesy of M. van Thiel, Nedschroef Herentals N.V.flow pattern in alloy 718. Etchant: 6 mL H2O, 60 mL HCl, produced during warm heading. Etchant: 6 mL H2O,and 6 g CuCl2. (b) Fold in the fillet of A-286. Etchant: 60 mL HCl, and 6 g CuCl2. Courtesy of F. Hogue, HogueMarble’s reagent. Courtesy of F. Hogue, Hogue Metallo- Metallographygraphy

388 / Cold Heading and Cold Extrusionseveral dies. After each stroke, the ejector pin the support fingers and the kickout pins during times stock diameter). The workpiece is cut topushes the workpiece out of the die. The transfer kickout. length in a separate operation in another machinemechanism grips it and advances it to the next and fed manually or automatically into the rodstation. Some of the progressive cold-heading Headers are classified as single stroke, dou- header. Reheaders are used when the workpiecemachines have special die stations for perform- ble stroke, or three stroke, based on the number must be annealed before heading is completed,ing finishing operations such as trimming, of blows (number of punches) they deliver to for example, when the amount of cold workingpointing, thread rolling, and knurling. Cold- the workpiece. Single-stroke and double-stroke needed would cause the work metal to fractureheading machines vary in terms of the number of headers have only one die, while the three-stroke before heading was complete. Reheaders aredies/stations, forging load, blank or wire size, headers have two dies. The punches in multi- made as either open-die or solid-die machines,blank cut-off length, speed, transfer mechanism, stroke machines usually reciprocate so that each single or double stroke, and can be fed byand special finishing capabilities, such as thread contacts the workpiece during a machine cycle. hand or hopper. Punch presses are also used forforming and knurling. Figure 8 shows a typical They are also further classified as open-die reheading.layout inside a six-die cold forming machine, headers or solid-die headers, based on whetherwith the punches located on the moving slide the dies open and close to admit the work metal Transfer headers are solid-die machines(lower left) and the stationary dies (middle) fixed or are solid. In single-stroke machines, product with two or more separate stations for variousto the bed. Figure 9 provides a closer view of the design is limited to less than two diameters of steps in the forming operation. Each station hastransfer mechanism, including specialized sup- stock to form the head. Single-stroke extruding its own punch-and-die combination. The work-port fingers used to transfer very short parts (e.g., can also be done in this type of machine. These piece is automatically transferred from onevalve-spring retainers) or stepped parts at high machines are used to make rivets, rollers and station to the next. These machines can performproduction speeds. Parts are supported between balls for bearings, single-extruded studs, and one or more extrusions, can upset and extrude clevis pins. Double-stroke solid-die headers can in one operation, or can upset and extrude inFig. 8 Punch and die layout in a six-station cold for- make short to medium-length products (usually 8 separate operations. Maximum lengths of stock to 16 diameters long), and they can make heads of various diameters headed in these machines mer. Courtesy of M. van Thiel, Nedschroef that are as large as three times the stock diameter. range from 150 mm (6 in.) with 10 mm (3/8 in.)Herentals N.V. These machines can be equipped for relief diameter to approximately 255 mm (10 in.) heading, which is a process for filling out sharp with 20 mm (3/4 in.) diameter. These machinesFig. 9 Support fingers to transfer very short parts (e.g., corners on the shoulder of a workpiece or a can produce heads of five times stock diameter square under the head. Some extruding can also or more. valve-spring retainers) or stepped parts at high be done in these machines. Because of theirproduction speeds. Parts are supported between the sup- versatility over single-stroke cold headers, dou- Bolt makers can trim, point, and roll threads.port fingers and the kickout pins during kickout. Courtesy of ble-stroke solid-die headers are extensively used Bolt makers usually have a cut-off station, twoM. van Thiel, Nedschroef Herentals N.V. in the production of fasteners. heading stations, and one trimming station served by the transfer mechanism. An ejector pin Single-stroke open-die headers are made for drives the blank through the hollow trimming die smaller-diameter parts of medium and long to the pointing station. The trimming station can lengths and are limited to heading two diameters be used as a third heading station or for extrud- of stock because of their single stroke. Extruding ing. In bolt makers, the last station in the heading cannot be done in this type of machine, but small area is a trimming station. The trimming die fins or a point can be produced by pinching in the (which is on the punch side) is hollow, and die, if desired. Similar machines are used to the die ejector pin drives the trimmed workpiece produce nails. completely through the die and, by an air jet or other means, through a tube to the pointing sta- Double-stroke open-die headers are made in tion. Pointers are of two types. Some have cutters a wider range of sizes than single-stroke open- that operate much like a pencil sharpener in die headers and can produce heads as large as putting a point on the workpiece (thus producing three times stock diameter. They cannot be used some scrap); others have a swaging or extruding for extrusion, but they can pinch fins on the device that forms the point by cold flow of the workpiece, when required. They will generally metal. The pointed workpiece is placed in a pinch fins or small lines under the head of thread roller. A bolt maker has a thread roller the workpiece when these are not required; if incorporated into it. The rolling dies are flat these fins or lines are objectionable, they must be pieces of tool steel with a conjugate thread form removed by another operation. on their faces. As the workpiece rolls between them, the thread form is impressed on its shank, Three-blow headers use two solid dies along and it drops out of the dies at the end, often as a with three punches and are classified as special finished bolt. machines. Having the same basic design as double-stroke headers, these machines provide Nut formers have a transfer mechanism that the additional advantage of extruding or upset- rotates the blank 180 between one or two dies or ting in the first die before double-blow heading all the dies. Therefore, both ends of the blank are or heading or trimming in the second die. Three- worked, producing workpieces with close blow headers combine the process of trapped dimensions, a fine surface finish, and improved extrusion and upsetting in one single machine to mechanical characteristics. A small slug of metal produce special fasteners having small shanks is pierced from the center of the nut, which but large heads. These headers are also ideal for amounts to 5 to 15% waste, depending on the making parts with stepped diameters in which design of the nut. the transfer of the workpiece would be accom- plished with great difficulty. Parts formers are flexible multistation machines designed for making a variety of cold- Rod headers and reheaders are two special formed parts. These machines may have up to six types of headers. Rod headers are open-die or seven stations, versatile transfer mechanisms, headers having either single or double stroke. and punch kickouts allowing them to make They are used for extremely long work (8 to 160

Cold Heading / 389complex parts. Parts formers are also equipped Open dies are made by machining the grooves Other important factors to consider in coldwith quick tool changing and can also handle before heat treating, then correcting for any heading tools are prestressing and venting. Diewire feed or slug feed. With these machines, distortion by grinding or lapping the grooves inserts are placed into radial compression by anvarious additional operations, such as extrusion, after heat treating. interference fit between the outside surface of thenotching, coining, and undercut forming, can be insert and the inside surface of the case (stressperformed on either end of the blank to produce In open-die heading, the dies can be permitted ring). Multiple inserts can be used for the highestcomplex net or near-net shaped parts at a very to grip the workpiece, similar to the gripper dies prestressing applications. Venting is necessary tohigh rate. in an upsetting machine. When this is done, the prevent trapping of air and lubricants in tools, backstop required in solid-die heading is not which can lead to increased tool pressuresTools necessary. However, some provision for ejection (decreased tool life) and problems with underfill. is frequently incorporated into open-die heading. More information on tool design and calculation The tools used in cold heading consist prin- methods can be found in Ref 3 and 67 to 73.cipally of punches and dies. The dies can be Design. The shape of the head to be formedmade as one piece (solid dies) or as two pieces in the workpiece can be sunk in a cavity in either Tool Materials(open dies), as shown in Fig. 10. the die or the punch, or sometimes partly in each. The decision on where to locate the cavity often Materials selection for dies and punches in Solid dies (also known as closed dies) consist depends on possible locations of the parting line cold heading is similar to cold extrusion (see theof a cylinder of metal with a hole through the on the head. It must be possible to extract the article “Cold Extrusion” in this Volume). Wearcenter (Fig. 10a). They are usually preferred for workpiece from both the punch and the die. It is resistance and toughness are the main propertiesthe heading of complex shapes. Solid dies can be generally useful, but not entirely necessary, to used in choosing cold-heading tools. Othermade entirely from one material, or can be made design some draft in the workpiece head for ease properties that must be considered includewith the center portion surrounding the hole as an of ejection. hardness, compressive strength, fatigue strength,insert of a different material. The choice of and stiffness. Also, it is important to understandconstruction depends largely on the length of the An important consideration in the design of the nature of the tool loading and ultimate failureproduction run and/or complexity of the part. For cold-heading tools is that the part should stay in mode when selecting materials, because this willextremely long runs, it is sometimes desirable to the die and not stick in the punch. Therefore, it is guide the selection process. For example, toolsuse carbide inserts, but it may be more eco- particularly difficult to design tooling for mid- that routinely fail by abrasion or galling neednomical to use hardened tool steel inserts in a shaft upsets. Where possible, the longest part of enhanced wear resistance, whereas tools that failholder of less expensive and softer steel. the shank is left in the die. There is less of a by chipping or fracture need additional tough- problem with open dies that use a special die- ness. More information about tool steels can be When a solid die is made in one piece, com- closing mechanism. Some punches are equipped obtained in Properties and Selection: Irons,mon practice is to drill and ream the hole to with a special synchronized ejector mechanism Steels, and High-Performance Alloys, Volume 1,within 0.076 to 0.13 mm (0.003 to 0.005 in.) of to ensure that the workpiece comes free. 1990, and Heat Treating, Volume 4, 1991, offinish size before heat treatment. After heat ASM Handbook or in the appropriate consensustreatment, the die is ground or honed to the Cold heading imposes severe impact stress ondesired size. Surface roughness for cold-heading both punches and dies. Minor changes in tool 0.870 3.12tools should be approximately Ra (average design often register large differences in tool life, 0.850roughness)=0.1 to 0.2 mm (3.9 to 7.9 min.), with as described in the following example. 0.160 1.75Rz (peak-to-valley height measurement)=1 mm(39 min.) maximum (Ref 65–67). Example 1: Improvements in Heading Tool 0.440 diam 7 –20 UNF –2A Design That Eliminated Tool Failure. The 0.430 –– Solid dies are usually quenched from the recessed-head screw shown in Fig. 11(a) was 0.320 16hardening temperature by forcing the quenching originally headed by the heading tool shown in 0.300 squaremedium through the hole, making no particular Fig. 11(b). After producing only 500 pieces, theattempt to quench the remainder of the die. By tool broke at the nib portion (“Point of failure,” (a) Workpiecethis means, maximum hardness is attained inside Fig. 11b).the hole; the outer portion of the die is softer and Point of failure H12, Rockwell C 45therefore more shock resistant. The design of the heading tool was improved Straight by adding a radius and a slight draft to the nib to 48 Because the work metal is not gripped in a (Fig. 11c). The entire nib was then highly T1,solid die, the stock is cut to length in one station polished. The redesigned tools produced 12,000of the header, and the cut-to-length slug is then to 27,000 pieces before breakage occurred, but (no taper) Rockwell C 60transferred by mechanical fingers to the heading this tool life was still unacceptable.die. In the heading die, the slug butts against a Sharp to 62backstop as it is headed. Ordinarily, the backstop A final design improvement is shown at the 0.005 R maxalso serves as an ejector. right in Fig. 11(c). The nib was made to fit a split Straight holder, using a slight taper to prevent the nib press fit Open dies (also called two-piece dies) con- insert from being pulled from the split holder assist of two blocks with matching grooves in their the header withdrew from the workpiece. Tools 0.002 to 0.004faces (Fig. 10b). When the grooves in the blocks of this design did not break and produced runs ofare put together, they match to form a die hole, as more than 100,000 pieces before the nib was (b) Original tool designin a solid die. The die blocks have as many as replaced because of wear.eight grooves on various faces so that as one T1 insert Backing plugwears, the block can be turned to make use of a 0° 30′new groove. Because the grooves are on the outer (polished) H12 bodysurface of the blocks, open-die blocks are 0° 30′quenched by immersion to give maximumhardness to the grooved surfaces. Open dies are 0.015 T1 nibusually made from solid blocks of tool steel, 0.020because of the difficulty involved in attempting R 0.004 Assembly was pressto make the groove in an insert set in a holder. (polished) taper per in. fitted until closed First improvement Final improvement (c) Improved tool designs (a) Solid die (b) Open dies Fig. 11 Improvements in heading tool design to Fig. 10 Cold-heading dies. (a) Solid (one-piece) and eliminate tool failure in the production of recessed-head screws. Dimensions given in inches (b) open (two-piece)

390 / Cold Heading and Cold Extrusionstandards (Ref 74–77), while cemented carbides consisting of moderate grain size (1.5 to 4.5 mm, amounts of chromium, molybdenum, tungsten,are discussed in Properties and Selection: Non- or 0.06 to 0.18 mils) and cobalt binder levels of 6 cobalt, and vanadium result in a large volumeferrous Alloys and Special-Purpose Materials, to 12%, which have been consolidated using hot fraction of carbide particles dispersed in theVolume 2 of ASM Handbook, 1990, and ICFG isostatic pressing. steels, which results in exceptionally high4/82 (Ref 78). strength and wear properties (Ref 80, 84–87). Shock-resistant tool steels, such as S1 and S7, Punches. Table 7 lists typical materials for are also used for the cold heading of tools, Dies and Inserts. W1 and W2 tool steels canvarious cold forming applications. Shallow- especially for the heading of intricate shapes be used for simple heading dies made withouthardening tool steels, such as W1 or W2 quen- when tool materials such as W1 and carbide have inserts. Inserts are commonly made from high-ched and tempered to 58 to 62 HRC, can be used failed by cracking. The shock-resistant steels are alloyed steels, such as D2, M2, and M4 (60 to 64for cone and finish punches as well as heading generally lower in hardness than preferred for HRC), or from tungsten carbide having a rela-punches that are not highly loaded. Air-hard- maximum resistance to wear, but it is often tively high percentage of cobalt (13 to 25%) forening grades A2 and D2 (59 to 61 HRC) or high- necessary to sacrifice some wear resistance to higher toughness. Improved tool steel perfor-speed steels such as M2 or M4 (61 to 63 HRC) gain resistance to cracking. When producing mance is obtained with P/M grades such as A11,provide improved hardness and wear resistance bolts that have square portions under the heads, M4, and T15, with the two latter grades espe-while maintaining adequate toughness. For high- or dished heads, or both, the right tool steel cially useful for operations with low lubricationspeed part formers where significant heat is selection is important to prevent tool failure. and high working temperatures. Carbides aregenerated and the coolant time is often limited, Newer-generation matrix high-speed steels and preferred for high-volume production and forgrades such as T15, HS 10-4-3-10, or HS 6-5-3-8 cold work tool steels with 8% Cr have been cold heading of difficult-to-form steels (highare superior to conventional tool steels. Tools successfully used as substitutes for grades such forming loads). Extrusion dies typically featureused for heading aluminum alloys are generally as D2 (12% Cr) or M2 (high-speed steel) when 12 to 25% Co binder, with upsetting diesnot as highly loaded, due to the lower flow improved toughness is needed (Ref 84, 88). requiring 20 to 25% Co for maximum toughness.stresses involved, hence punches are made fromlower-hardness tool steels such as S1 (54 to 56 Tool steels produced by the powder metal- Support Tooling. Kickout pins (ejectors) areHRC) or H13 (50 to 52 HRC), with D2 being lurgy (P/M) process provide superior perfor- typically made from O1 or A2 hardened to 59 toused for worst-case applications. mance compared to conventional wrought 61 HRC. Pins that must support large loads products due to lack of segregation, smaller during heading or extrusion may be produced Applications that entail high loads and wear, primary carbide size, uniform distribution of from M2 hardened to 61 to 64 HRC. Pressuresuch as extrusion punches and mandrels, carbides, and fine grain size. Proprietary P/M pads may use a number of steels, depending onindenting punches for recessed-drive fastener grades are available from a number of tool steel the specific environment (Table 7). Cutters andfeatures, and piercing pins, are often produced producers that offer substantial improvements in quills can be fabricated using tool steels, butfrom cemented carbides due to their much wear resistance while maintaining toughness carbides have better resistance to wear and dul-higher compressive strength and wear resistance. equal to conventional grades, such as M2 or D2. ling. In assemblies, inner stress rings are usuallyOptimal performance for carbides in these The combination of very high carbon levels made from H13, D2, or M2, and outer stress ringsapplications is provided by microstructures (often greater than 2 mass %) and considerable and cases are made from H13 or L6. Designs that require significant press fits in order to generateTable 7 Typical tool materials for cold forming applications the desired preloads use maraging steels heat treated to ~54 HRC.Operation Typical grade Alternate grades Coatings have become a significant part ofHeading punches W1, W2 at 58–60 HRC A2 or M2 at 59–61 HRC; M4 at 61–63 HRC the tool engineering process. Thin-film coatings (cone, finish, upset) deposited by the chemical vapor deposition M2 at 60–64 HRC M4 at 62–66 HRC; M42 at 65–70 HRC; HS 6-5-3-8 at (CVD) and physical vapor deposition (PVD)Indenting and extrusion 63–67 HRC; cemented carbides with 6–12% Co processes are commonly applied to all types of punches/pins M2 at 58–62 HRC tool steel and carbide components, with the most A2, D2 at 58–62 HRC; M3 : 2 at 61–63 HRC; frequently used being the PVD coatings TiN,Piercing W1 at 58–62 HRC T15 or T42 at 63–66 HRC TiCN, and TiAlN. Wear-critical parts, such as extrusion punches and recessed-drive indentingDies and inserts M2 at 60–64 HRC A2, D2, M2 at 58–64 HRC; M4, A11 at 62–65 HRC; punches, have such significantly improved tool O1, O2 at 59–61 HRC T15 at 63–66 HRC; cemented carbides with 12–25% Co life that they should always be coated. Table 8Trim dies L6 at 57–60 HRC compares the various coatings and processes.Kickout pins (ejectors) M2, M4 at 58–60 HRC T1 at 60–64 HRC; cemented carbides with 12–25% Co The advantages for the PVD method should beFiller (die segments) A2, M2 at 59–63 HRC; D2 at 58–60 HRC noted: Low process temperature results in noPressure pad (backing A2, M2 at 59–63 HRC D2 at 58–60 HRC dimensional changes after final tempering; thin H13 at 55–56 HRC D2 at 60–62 HRC; M2 at 63–65 HRC; coatings do not impair tolerances during form- plate, bushing) H13 at 45–50 HRC ing; and polishing after coating is not alwaysQuills, cutters T15 at 64–66 HRC necessary. However, carefully controlled pol-Cases (inner stress rings) Cemented carbides with 6–20% Co ishing after coating further improves the frictionCases (outer stress rings) M2 at 59–62 HRC; D2 at 56–58 HRC properties and reduces galling. L6 at 42–45 HRC; maraging steel SAE AMS 6514 (UNS Table 9 provides further information on a K93120) at 54 HRC range of PVD coatings. Tool steels that are tempered at low temperatures, such as W1, O2,Source: Ref 65–67, 78–88 and S7, generally cannot be coated for improved surface wear properties (Ref 66, 85, 89). TheTable 8 Typical tool coatings and deposition processes CVD and PVD processes and the subsequent heat treating methods must be carefully con-Coating materials Chemical vapor deposition Physical vapor deposition Thermoreactive deposition trolled to prevent grain growth and carbideThickness, mm (mils) and diffusion coarsening in tool steels, which significantlyCoating temperature,C (F) TiC, TiCN, TiN TiN, TiCN, TiAlN degrade wear resistance and fatigue strengthHeat treatment of substrate steel 5–10 (0.2–0.4) 1–5 (0.04–0.2) VC (Ref 90, 91).Distortion 950–1050 (1740–1920) 480–550 (900–1020) 2–15 (0.08–0.6)Surface polishing After coating Before coating 850–1050 (1560–1920) Severe Minimal After coatingSource: Ref 66, 84, 89 Necessary Not always necessary Severe Necessary

Cold Heading / 391Preparation of Work Metal (Ac1) holding for a suitable time, and then slow Both ferrous and nonferrous precipitation- cooling. This process does not produce a specific hardening alloys are frequently solution heat The operations required for preparing stock microstructure or surface finish. Spheroidize treated prior to forming and then subsequentlyfor cold heading may include heat treating, annealing consists of prolonged heating near or age hardened. Aluminum alloys that have beendrawing to size, machining, descaling, cutting to slightly below the Ac1 temperature, followed by fully annealed (O temper) must be completelylength, and lubricating. slow cooling, and produces a microstructure heat treated after forming (solution heat treat- consisting of spheroidal (globular) cementite ment, quench, and age) in order to develop Heat Treating. The cold-heading properties distributed throughout the ferrite matrix. Spher- maximum properties (T6 temper) (Ref 99). Moreof most metals are improved by some form of oidizing has conventionally been performed information on heat treating methods for steelsthermal treatment after hot rolling. The steel using either batch (bell or carbottom furnaces) or and nonferrous metals is described in Heatcold-heading industry has developed the fol- long continuous (pusher-type or roller-hearth) Treating, Volume 4 of ASM Handbook, 1991,lowing conventions for describing wire (Ref 21): furnaces, with batch roller-hearth furnaces (short and in Ref 61 and 99 to 104. time cycle) having been more recently intro- DD: direct drawn from wire rod or bar duced (Ref 92). Drawing to size produces stock of uniform DFAR or DFAB: drawn from annealed rod cross section that will perform as predicted in Typical processing time for spheroidizing is dies that have been carefully sized to fill out or bar from 12 to 24 h, making it by far the most time- corners without flash or die breakage. Tolerances DFSR or SFSB: drawn from spheroidize- consuming stage in steel part production for diameter and out-of-roundness are important (Ref 93–98). Both intercritical and subcritical factors in controlling the volume of metal to be annealed rod or bar process cycles are used, with the intercritical worked and are included in various industry AFS or SAFS: drawn to size and annealed or process being more susceptible to decarburiza- standards (Ref 21, 28, 29, 105–110). Out-of- tion and high energy consumption due to the round wire may cause localized die wear show- spheroidize annealed higher temperatures involved. Hypereutectoid ing up as wear rings in the drawing die. The AIP or SAIP: drawn, annealed, or spheroidize steels such as SAE 52100 require intercritical elliptical cross section produces nonuniform annealing in order to break up coarse proeutec- cold work around the circumference of the wire, annealed in process and finally lightly drawn toid cementite. which contributes to distortion of the product and to size causes strength and ductility variation through the cross section (Ref 21). Regular annealing is performed by heatingwire near or below the lower critical temperature Manufacturers often produce wire and wire rod with reduced tolerances. Figure 12 shows aTable 9 Typical physical vapor deposition tool coating properties comparison of diameter tolerances (total) for steel wire and wire rod products. Some steel TiN TiCN TiAlN WC/C manufacturers have developed precision rolling techniques that can produce wire rod with dia-Hardness, HV 0.05 2000–3000 3000–4000 2500–3500 1000–1200 meter tolerances as low as 0.20 mm (0.008 in.)Coefficient of friction 0.4 0.4 0.4 0.2 (Ref 111–113). Drawing to size also improves strength and hardness when these properties are against steel (dry) 1–4 (0.4–1.6) 1–4 (0.4–1.6) 1–5 (0.4–1.6) 1–4 (0.4–1.6) to be developed by cold work and not by sub-Thickness, mm (mils) 600 (1110) 400 (750) 800 (1470) 300 (570) sequent heat treatment. This is very important forMaximum working nuts and other threaded fasteners, because Gold-yellow Blue-gray Violet-gray Black-gray insufficient strain hardening during wire drawing temperature, C (F) Monolayer Graded multilayer Multilayer or Graded can result in failure to meet specificationCoating color requirements.Coating structure 1· 1.35 · monolayer multilayer 1.35–1.5 · 1.5 · While a fully spheroidized microstructure isApproximate cost desirable for formability, steel wire is rarely used in the as-spheroidized condition, due to the poorSource: Ref 89 coil configuration, the formation of a shear lip during cutoff, and the potential for undesirable 1.4 bending of long sections during upsetting (Ref 21). For these reasons, almost all material is G 3509 given a light wire-drawing reduction (skin pas- 1.2 sing), usually in the range of 3 to 8% but often as high as 20%, after the thermal treatment (Ref 21, JIS G 3509 cold-heading 54, 60, 80, 114, 115). This wire drawing can be 1 wire rod performed either by the wire producer or in front of the forming operation, depending on the wireTolerance, mm JIS G 3509 low-alloy size and application. Wire drawing in front of the header can decrease costs (Ref 116, 117) and steel cold-heading wire reduce strain aging (Ref 73, 118, 119). 0.8 Precipitation-hardening alloys, such as ASTM F 2282 cold- MP35N or A-286, that are used for high-strength threaded fasteners can be processed with large heading wire rod cold reductions after solution treating, as high as 20 to 36% for MP35N (Ref 120) and 50 to 60% 0.6 F 2282 ASTM F 2282 cold- for A-286 (Ref 115). The strains in the cold- worked areas promote increased precipitation heading wire hardening and higher strength. Metallurgical defects, such as central bursting and redundant 0.4 EN 10218-2 steel wire 0.2 EN 10218–2 20 30 40 G 3509 60 Wire or rod diameter, mm F 2282 0 50 0 10Fig. 12 Total permissible variation in wire or rod diameter as a function of specified diameter

392 / Cold Heading and Cold Extrusionwork produced during drawing, can degrade Acid pickling is usually the least expensive mation on shearing and cropping is available inworkability (Ref 121–124). method for complete removal of heavy scale. Ref 128 and 129. For larger diameters, sawing is Improved descaling during batch pickling of generally used. Gas cutting and abrasive-wheel Aluminum alloy wire is usually supplied in a coils is obtained when the individual loops are cutting are considered obsolete and no longerstrain-hardened temper such as H13 in order to separated on the hook in order to allow complete used in contemporary applications.increase the column (buckling) strength, surface contact with the acid. Vibration orimprove the resistance to scratching and inden- oscillation during pickling of larger-weight coils Figure 13 shows examples of steel blanks thattation during handling and feeding, and to may be used instead of unbanding them. Also, were sheared using a high-speed impact cutoffimprove the cutoff edge during shearing (Ref 46, rinsing the coils with a high-pressure spray after mechanism (velocity ~1 m/s, or 197 ft/s). Due to125). The H12 temper, also called quarter hard, is an immersion rinse removes residual acid and the very high cutting speed, there is little defor-produced by cold drawing approximately 20% smut. Additional information can be found in the mation or damage to the end of the wire, evenafter annealing, with the H14 (half-hard) temper article “Pickling and Descaling” and the articles when cutting short blanks from spheroidizedtypically reduced 35% after annealing. The H13 on cleaning and finishing of specific metals in material. When combined with a linear feedtemper is intermediate between these two. Surface Engineering, Volume 5 of ASM Hand- mechanism that eliminates the need for a wireAnnealed wire (O temper) is used for applica- book, 1994, and in Ref 126 and 127. stop, improved volume control (Fig. 14) andtions requiring maximum formability. minimal work hardening of the slug ends occur. Cutting to Length. In a header that has a In many cases, this eliminates the need to square Turning and Grinding. Drawn wire can have shear-type cutoff device as an integral part of the up the blank in the first station.defects that carry over into the finished work- machine, cutting to length by shearing is a part ofpiece, exaggerated in the form of breaks and the sequence. In applications in which cutting to Coating and Lubrication. Although some offolds. Seams in the raw material that cause these length is done separately, shearing is the method the more ductile metals can be successfully colddefects may not be deep enough to be objec- most commonly used for bars up to approxi- headed to moderate severity without lubrication,tionable in the shank or body of a bolt but can mately 50 mm (2 in.) in diameter. More infor- most metals to be cold headed are lubricated tocause cracks in the head during cold heading or reduce forming loads, prevent galling andsubsequent heat treatment. Surface seams, laps,and other defects can be removed by turning, Number of pieces 10 Cutoff mass variation for 10B22 steelgrinding, or shaving at the wire mill or by 8 blank 19 mm ϫ 33 mmmachining the headed product. A typical amount 6of removal would be 0.2 to 0.5 mm (0.008 to 4 Blank mass, g0.02 in.), for a total diameter reduction of 0.4 to 2 72.651.0 mm (0.016 to 0.04 in.). Applications that use 0 72.66shaved wire include aerospace and specialty 72.67fasteners, bearing races, and engine poppet (a) 72.68valves (intake and exhaust). 72.69 72.70 Descaling. Work metal that has been heat 72.71treated usually needs to be descaled before cold 72.72heading. Scale can cause lack of definition, 72.73defects on critical surfaces, and dimensional 72.74inaccuracy of the workpiece. Methods of des- 72.75caling include abrasive blasting, waterjet blast- 72.76ing, pickling, wire brushing, and scraping. 72.77Selection of method depends largely on theamount of scale present and on the requiredquality of the surfaces on the headed workpieces. 12 Cutoff mass variation for steel blank 10 22.3 mm ϫ 104 mm Number of pieces 8 6 4 2 0 333333333333333333331111111111111111111177777777777777777777....................2223111223312222311278690122434567189013Fig. 13 Improved volume control with minimal Blank mass, g deformation and work hardening of the cutoff (b)ends due to high-speed impact cutoff combined with alinear feed that eliminates the need for a wire stop. Courtesy Fig. 14 Cutoff accuracy (volume control) demonstrated for two parts. (a) 50 consecutive blanks taken off a four-die,of M. van Thiel, Nedschroef Herentals N.V. 4000 kN (450 tonf) cold former making gear blanks at a rate of 115 pieces/min. Average mass is 72.71 g (2.56 oz) with a maximum variation of 0.12 g (0.004 oz). (b) 55 consecutive blanks taken on a five-die cold former running at a rate of 80 pieces/min. Average mass is 317.23 g (11.19 oz) with a maximum variation of 0.22 g (0.008 oz). Source: Ref 116, 130

Cold Heading / 393sticking in the dies, and avoid excessive die with backward or multiple forward extrusions or aluminum stearate (Ref 137). For the mostwear. There are a number of coatings applied to requiring coating weights of at least 10 g/m2 in severe forming, similar coatings and practices toheading stock, depending on alloy type and the order to provide separation between the tools and those described for stainless steels are used. Thenature of the forming, such as lime or borax workpiece even after considerable surface coatings are later removed with nitric acid.coatings, zinc phosphate or oxalate conversion expansion has occurred.coatings, film layers of stearate soaps or The more formable nickel-base alloys aremolybdenum disulfide (MoS2), and plating with The AFS/SAFS wire is usually coated with a usually also copper plated. If the heading is notsofter metals such as copper (Ref 131). Newer reactive sodium stearate lubricant after phos- severe, however, they can be headed with adry-film coatings consisting of acrylic and phating, with the reacted layer forming an inso- stearate coating only, which can be removed withpolyolefin polymers have gained acceptance due luble zinc stearate. This reacted layer typically hot water. Nitric acid cannot be used on Monel,to their ease of cleaning and environmental has a coating weight of approximately 0.8 to because the acid will attack the base metal.friendliness, in addition to their lubricating 2.2 g/m2, and the excess sodium stearate layer isqualities. typically 1.1 to 2.2 g/m2. The total layer thick- Copper-base alloys have the least need for ness is usually less than 10 mm (0.4 mils) thick. lubrication. For light heading operations, a Lubricants are typically mineral oils, or syn- This product is intended to be drawn in front of compounded oil containing natural fat is added atthetic oils, because most water-emulsifiable the cold header prior to forming. the header. For more severe heading and extru-compounds have inadequate film strength or sion, calcium or sodium stearate coating can bewettability to prevent contact between the Liquid lubricants are extremely important added during the last draw of the wire. Sulfurizedworkpiece and the tools, especially during heavy when any forming of the sheared ends takes oil should not be used for cold heading of copper-extrusion operations. Lubricant oils are com- place, especially during multiple extrusion base alloys unless some staining can be tolerated.pounded with polar additives, such as fatty acids operations. The lubricants are applied to theand esters, in order to wet the metal surfaces, as workpieces and tools by means of flooding and Aluminum header wire is generally coatedwell as other modifiers, such as extreme-pressure spraying. They are particularly necessary during with zinc or calcium stearate. Aluminum needs(EP) additives, antifoaming and antibacterial heading and extrusion of difficult-to-form metals more lubrication for cold heading than copperagents, detergents, and antioxidants (Ref 131– such as work-hardened precipitation-hardening but much less than nickel. Specially formulated133). Due to environmental concerns with EP stainless steels and nickel-base superalloys. synthetic oils are typically used on machinesadditives based on chlorinated paraffins, olefins, dedicated to forming aluminum parts.or fatty oils, lubricants are being replaced by Stainless steels and specialty ferrous alloysnewer formulations, usually with EP additives such as A-286 are usually electroplated with 2 to Titanium-base alloy wire usually has a MoS2-based on sulfur and including increased amounts 2.5 mm (0.08 to 0.10 mils) of copper (applied base lubricant coating applied after drawing.of friction and antiwear modifiers (Ref 134). over a nickel strike) and then lubricated with oil/ Mineral oils with high-temperature oxidative grease, soap, or molybdenum disulfide (Ref 81, stability are used to supplement the wire coating Coatings for carbon and alloy steel bars, wire 115). Simple upset heads can be accomplished during automatic forming on horizontalrods, and wire that are thermally treated at fin- with either precoat or lime coatings that have machines. When warm or hot heading slugs thatished size (AFS, SAFS) include lime (CaO) or been drawn in soap or grease. Precoat is an have been cut from bar, the lubricant typically isborax (hydrated sodium borate), zinc phosphate aqueous dip of potassium or sodium sulfate salt applied directly to the dies in the form of a paste.plus lime, zinc phosphate plus reactive or non- that forms a crystalline coating on the metal Ceramic glass precoats are used at the highestreactive stearate, or zinc phosphate plus lime and surface. forming temperatures. See the article “Forging ofpolymer. If cold drawing is the final operation Titanium Alloys” in this Volume for more(AIP, SAIP), a drawing compound consisting of The MoS2 coatings (drawn in soap or grease) information.calcium or aluminum stearate, possibly with an are used for typical upsets and when sharperaddition of MoS2 for severe upsetting or extru- corners need to be filled. The most severe In all cold heading, the best practice is to usesion, is applied in the die box. This produces a forming requires a thicker copper layer (3 to the simplest and the least lubricant that willdry, hard, nongummy film that minimizes slip- 10 mm, or 0.12 to 0.4 mils) plus MoS2 that is provide acceptable results, for two reasons:page during the feeding process at the header and either applied to AFS wire or to AIP wire that isreduces the potential for die clogging. subsequently skin passed (3 to 5% reduction) in a  Excessive amounts of lubricant may build up drawing soap. Induction heating of stainless and in the dies, resulting in scrapped workpieces Upsets of low to moderate severity can be specialty alloys for warm forming requires cop- or damaged dies.produced with material using lime and soap per plating plus MoS2, because the higher tem-coatings, sometimes augmented by oils or grea- perature exceeds the capabilities of other  Removal of lubricant is costly (the cost ofses applied to the wire upon entering the forming lubricants. removing lubricant usually increases in pro-machine. Lime is applied after pickling by dip- portion to the effectiveness of the lubricant).ping the coils in a 2 to 12% suspension of lime in Normal hot alkaline cleaning will not removewater at approximately 80 C (180 F). Thicker electroplated copper, which necessitates the use Surface Engineering, Volume 5 of ASM Hand-coatings are obtained by dipping and drying up to of nitric acid immersion. The other coatings can book, 1994, has more information regardingthree times. The roughness of the coating pro- generally be removed with alkaline cleaners. appropriate cleaning and finishing techniques.motes adhesion of lubricants such as drawingcompounds and dry-film polymers. The presence of a passive oxide film on these Complex Workpieces alloys means that they are not easily phosphated, While these finishes are widely employed, so oxalate coatings are used instead. A typical Cold-headed products that have more than onephosphate coatings are frequently used for the application consists of 5 to 8 mm (0.2 to 0.3 mils) upset portion need not be formed in two headingmore demanding applications (Ref 21, 54, 78, of oxalate with a stearate soap or MoS2 lubricant operations; many can be made in one operation114, 135, 136). Phosphate coatings have a wide layer on top. The use of oxalate coatings is on the of a double-stroke header. The length of stockrange of crystal shapes and coating weights/ decline due to environmental reasons. that may be partly upset is generally limited tothicknesses, with most cold forming applications five times the diameter of the wire. The onlybased on fine-grained, iron-free crystals yielding Lubrication in Cold Heading of Nonferrous other limitation is that the header must be able tocoating weights between 5 and 15 g/m2 and layer Alloys. In the cold heading of nonferrous metals, accommodate the diameter and length of wirethickness of 2 to 15 mm, (0.08 to 0.6 mils). The the need for lubrication varies from metal to required for the workpiece.coating should be dense and completely cover metal. Nickel-base alloys, especially the high-the surface, with no bare spots. Typical upsetting strength alloys, require very good lubrication. Three pieces, each with two end upsets thatand light extrusions use lower coating weights, These metals are usually copper plated with were made completely in one operation in a thicker coatings (6 to 10 mm, or 0.2 to 0.4 mils) double-stroke open-die header, are shown in and then given a light skin pass in any of the dry soap powders containing sodium, calcium,

394 / Cold Heading and Cold ExtrusionFig. 15(a). These parts were made at a rate of edges and corners of the square portion and a moved into the open position by the ejector(s) in80 pieces/min. Production rate is limited only by complete absence of burrs or fins in the collar the punch, and the punch pin remains in thethe speed of the machine used, not by the item area. In heading, any excess pressure applied on forward position to keep the blank pressed intobeing produced. the collar portion to fill the corners and edges of the die. the square resulted in flash or overfill on the The product becomes more expensive when collar portion. It was necessary to upset the collar Blank rotation is a tooling feature that rotatesthe upsetting operation has to be performed portion in one blow and to form the square in a the workpiece from a horizontal to a verticaltwice, as in production of the 710 mm (28 in.) second blow in order to fabricate this part suc- orientation, allowing forming operations to belong axle bolt shown in Fig. 15(b). This part cessfully (Fig. 16). The folds generally produced performed at 90 to the original axis (Ref 141).required two upsetting operations, because the by this technique were avoided by careful control Figure 18 shows the cold forming progressiondie in a standard double-stroke cold header was of size. By forming the collar completely during used to produce an M6 eyebolt blank. The pro-not long enough to form both upsets in the the first blow and almost completely confining it cess starts with a conventional cutoff blank,machine at the same time. One or more addi- during the second blow, the remainder of the followed by forward extrusion at the firsttional operations may be needed for workpieces metal was controlled so that it could be directed operation and upsetting/forward extrusion at thethat require pointing as well as a complex upset. into filling the square. Therefore, the pressure second operation. The third operation consists of needed to form and fill the square was confined to a 90 rotation of the blank, with no forming Center Upsetting. Most cold heading in- this area and not allowed to cause further taking place. The fourth hit flattens the eye sec-volves forming an upset at the end of a section of upsetting in any other portion. Accurate control tion, with the last hit piercing the center of therod or wire. However, the forming of upsets at of the headed volume depended on the accuracy eye. Figure 19 shows the actual part progressionsome distance from the end is common practice. of the cut blank and of the collar formed in the during forming on a five-die, 690 kN (78 tonf) first blow. cold former running at 250 strokes/min. The trailer-hitch-ball stud shown in Fig. 15(c)is representative of an upset performed midway Segmented Dies, Multiple Upsets, and Economy in Cold Headingbetween the ends of the wire blank. This stud was Blank Rotation. Segmented die forming isupset and extruded in two strokes in a 19 mm capable of producing parts with multiple upsets, Cold heading is an economical process(3/4 in.) solid-die machine. The diameter of one notches, grooves, formed or pierced holes on because of high production rates, low labor costs,end section is smaller than that of the original different axes, and non-symmetrical features and material savings. Production rates rangewire, and the round center collar is flared out to with offset axes (Ref 3, 138–140). The latter twomore than 21/2 times the wire diameter. The variations still use standard machine motion and 6.140 1038 steelcenter-collar stud shown in Fig. 15(d) is another transfer, because the secondary axis is parallel to 6.125 (annealed)example of a center upset. Both ends of the stud the primary axis. Figure 17 illustrates how mul-were extruded below wire size, while the center tiple upsets can be produced using segmented Slug 0.395collar was expanded to more than three times the dies and an air-loaded punch pin. The air-loadedoriginal wire diameter. This stud was formed in punch pin pushes the blank into the die while the 1136 0.170 0.645three strokes in a progressive header. rest of the punch tooling is moving toward the 0.640 die. The inserts are closed by axial movement Control of the volume of work metal to pre- along the tapered grooves, due to the punch case Ejector 5 3–8 Dievent formation of flash and to prevent excessive making contact with the stationary die. Once theloads on the tools is important in most cold- moving die segments reach their fully closed First blow (upset)heading operations. In center upsetting, control position, the punch tooling is now fixed, and a Punchof metal volume is usually even more important, cavity is formed in the desired shape of the newnot only to prevent flash and tool overload but upset. Continued advancement of the punch pinalso to prevent folds. A technique used suc- now upsets the secondary head. The cycle iscessfully in one application of center upsetting is completed as the punch case begins to recededescribed in the following example. from the stationary die, the insert segments are Example 2: Production of a Complex Cen-ter Upset in Two Blows. A blank for a bicycle-pedal bolt (Fig. 16) required sharp corners on the1 diam 28 3–4 8– diam 1– 0.421 Second blow 0.552 sq 4 0.548 2 (b) Each end upset in a separate operation 5.129 4.135 –1 diam 4 First upset Second upset and 0.458 0.390 0.658 extruded diam Sharp corners 0.654 (c) Center upset and one end extruded Completed workpiece 1 78–4–1 diam First upset 2 4–1 Second upset and extruded Third upset and extruded(a) Both ends upset (d) Center upset and one ends extruded Fig. 16 Production of a 1038 steel blank for a bicycle- in one stroke pedal bolt in two blows on a cold upsetter.Fig. 15 Typical part with center upsets or upsets at both ends. Dimensions given in inches Dimensions given in inches

Cold Heading / 395from approximately 2000 to 50,000 pieces/h, savings is considerable (see the section “Com- by producing the component by cold headingdepending on part size. Fewer machines are bined Heading and Extrusion” in this article). rather than machining. The same shape andneeded to meet production requirements than Subsequent machining or finishing of the cold- dimensional accuracy were produced by bothwith other processes, resulting in reduced costs headed parts is usually not necessary. This can be methods. In both cases, threads were rolled in afor equipment, maintenance, and floor space. especially beneficial when relatively expensive separate operation.Labor costs are minimal, because most opera- work materials are used. The following examplestions are performed automatically, requiring describe the replacement of machining by cold Example 4: Cold Forming of a Connectinglabor only for setup, supervision, and parts heading to fabricate parts with reduced produc- Sleeve. A connecting sleeve was originallyhandling. tion costs. produced by machining from bar stock, with an input mass of 120 g, (4 oz) and subsequent scrap Material savings results from the elimination Example 3: Machining Replaced by Cold of 74.2 g, (2.6 oz). The cold formed part canor reduction in chips produced. Typical scrap Heading to Save Material. A blank for a be produced on a 1700 kN (190 tonf) forminglosses are 1 to 3%, with the only waste coming threaded copper alloy C10200 (oxygen-free machine from an initial blank 20 mm (0.8 in.) infrom piercing and trimming. When cold heading copper) nozzle component (Fig. 20) was origin- diameter and 11 mm (0.4 in.) long (mass=49 g,is combined with other operations, such as ally produced by machining from bar stock. A or 1.7 oz) at a rate of 130 strokes/min. Scrapextrusion, trimming, and thread rolling, the material savings of more than 50% was effected from the piercing operation is only 3.2 g (0.11 oz). The forming sequence for the con- Double upset with necting sleeve (Fig. 21) is as follows: segmented inserts  Operation 1: Preparation and centering for 85.73 backward extrusion 9.42  Operation 2: Combination forward and backward extrusion Caster stem  Operation 3: Backward extrusion and form-Front view ing of the hexagonal section Air-loaded pin  Operation 4: Extrusion of the splined section Punch  Operation 5: Piercing station Tool Reverse Forming case Reverse forming consists of forming a shape by upsetting or extruding into a die mounted on the moving press ram with a punch tool mounted Inserts DieFig. 17 Process sequence for upsetting a second head on a caster stem. Courtesy of J. Bupp, National Machinery Co. Fig. 19 Sequence of forming operations, including blank rotation, during the manufacture of an M6 eyebolt. Courtesy of J. Bupp, National Machinery Co. 8–7 diamFig. 18 Process sequence used to cold head an M6 eyebolt. Process proceeds from right to left and consists of wire 2 –12 cutoff, forward extrusion, heading/forward extrusion, blank rotation, upsetting/flattening, and piercing. Fig. 20 Copper alloy C10200 nozzle componentCourtesy of J. Bupp, National Machinery Co. blank that was originally machined but was switched to cold heading to save the work metal indicated by the shaded regions. Dimensions given in inches

396 / Cold Heading and Cold Extrusionon the stationary segment. Reverse forming is contained heading, combined operations), the State-of-the-art production techniques canused frequently to increase forming speeds on severity of upset or extrusion, the length-to-dia- produce parts with feature-to-feature lengthshort or complex parts that are difficult to grip meter ratio of the blank, the type of metal being variations of only +0.05 mm (0.002 in.), butand transfer (Fig. 22). It is also used to convert formed, and the quality of the tooling and more typical values for small parts (550 mm, or180 transfer processes into straight-across pro- machine. Work can be produced to much closer 2 in.) are +0.13 mm (0.005 in.). Total partcesses when upsetting and extrusion operations tolerances in cold headers than in hot headers. length variations down to +0.25 mm (0.010 in.)are required. Tooling arrangements are used on Tolerances on parts produced by single-stroke are possible for small parts and between +0.38machines with an appropriate working stroke headers need to be greater than on parts given and 0.80 mm (0.015 and 0.03 in.) for longerthat will allow parts to be held between the punch two or more blows. Rivets, often formed in sin- parts. Concentricity as measured by total indi-and die kickout pins, fully supported, as the press gle-stroke machines, have tolerances of cated runout (TIR) can be as low as 0.03 toslide withdraws (Ref 142). +0.38 mm (0.015 in.), except where otherwise 0.07 mm (0.001 to 0.003 in.) for parts using specified. Shanks for rolled threads often are advanced reverse forming methods; conven- Example 5: Manufacture of a Fastener allowed only +0.038 mm (0.0015 in.). Small tional practices produce values of i0.15 mmUsing Reverse Forming Method. Figure 23(a) parts can usually have closer tolerances than (0.006 in.). For longer shafts and boltsshows the part sequence that was developed to large parts. (length 4200 mm or 8 in.; length/diameter ratioform an M10 · 1 pipe screw. The part is made ~25 to 1), TIR is of the order of 6 mm/mmfrom predrawn, phosphated SAE 1008 wire at a Diameter tolerances as close as +0.013 mm (0.2 mil/in.) of length or more without sub-production rate of 200 strokes/min. The initial (0.0005 in.) can be obtained on solid sections by sequent straightening. Figure 25 is an examplecutoff blank is 14.5 mm (0.57 in.) long and using precision sizing (ironing) dies, although of a single-side aerospace fastener that is pro-9 mm (0.35 in.) in diameter. This speed is maintenance of a tolerance this close increases duced to very tight tolerances using precisionattainable because the first two forming opera- product cost; requires careful control of cold forming methods.tions are performed in dies on the moving slide, machines, tools, and work metal; and is unusualavoiding a 180 transfer (Fig. 23b). The final part in practice. More typical values for trap-extruded The following example demonstrates toler-is 16 mm (0.6 in.) long and 11 mm (0.4 in.) diameters are +0.05 to 0.08 mm (0.002 to ance capabilities and shows dimensional varia-across the flat dimension. 0.003 in.). Diameters produced by open heading tions obtained in production runs of specific can usually be controlled to a tolerance of +0.18 cold-headed products.Dimensional Accuracy to 0.38 mm (0.008 to 0.015 in.), whereas a tighter tolerance of +0.08 to 0.13 mm (0.003 to Example 6: Variation in Dimensions of a Part tolerances that can be achieved in cold 0.005 in.) is achievable if the head can be con- Valve-Spring Retainer Produced in a Nutheading are dependent on a number of variables, tained at least partially in the die (Ref 143–145). Former. The valve-spring retainer shown inincluding the type of forming (open heading, Figures 24(a) and (b) show representative toler- Fig. 26 was produced from fine-grained alumi- ances that can be obtained on cold formed parts. num-killed 1010 steel (No. 2 bright annealed, cold-heading quality) in a five-station pro-Fig. 21 Cold forming sequence used to produce connecting sleeve. Courtesy of T. Christoffel, Hatebur Metalforming gressive nut former. To determine the cap- abilities of the machine and tools for long-run Equipment, Ltd. production, several thousand pieces were made from three separate coils. Distribution chartsConventional method Transfer Reverse forming method were prepared for two critical dimensions on grip randomly selected parts made from each coil.Tool pin Die pin Transfer Results are plotted in Fig. 26. Lots 1, 2, and 3 Die Tool Tool grip include parts made from the three different coils. As a further test of machine and tool capabilities, Die the tooling was set to a mean taper dimension for lot 1, high side for lot 2, and low side for lot 3. Die pin Tool pin The accuracy that could be maintained onFront Kickout Front Transfer thickness of a flat surface is demonstrated indead position dead closed Fig. 26. Although specifications permitted a totalcenter center position variation of 0.51 mm (0.020 in.) on seat thick- ness, actual spread did not exceed 0.13 mm Part falls prior to transfer closing 100% transfer control (0.005 in.) for parts made from the three coils. A greater total variation was experienced for theFig. 22 Comparison of conventional forming method with reverse forming method. Courtesy of J. Bupp, National taper-depth dimension. When the tools were set for mean, the total variation was 0.33 mm Machinery Co. (0.013 in.), which was still within the 0.41 mm (0.016 in.) allowable (lot 1). With tools set for high side, total variation was only 0.25 mm (0.010 in.), although one part was 0.025 mm (0.001 in.) out of the allowable range (lot 2). Optimal results were obtained on the taper dimension when tools were set for the low side (lot 3); total spread was only 0.18 mm (0.007 in.). Surface Finish Surfaces produced by cold heading are gen- erally smooth and seldom need secondary operations for improving the finish. Surface

Cold Heading / 397roughness, however, can vary considerably polished tools. The best finish is on the top of the produced by heading the slug and simulta-among different workpieces or among different head and on the extruded shank, while the neously extruding the opposite end to 13.34 mmareas of the same workpiece, depending on: poorest finish is on the outer periphery of the (0.525 in.) in diameter, by coining and trimming round head. Using the peak-to-valley height the round head to a hexagonal shape, and by Surface of the wire or bar before heading measurement, Rz, values of 10 to 63 mm (390 to turning the bolt blank to 8.4 mm (0.331 in.) in Amount of cold working in the particular area 2480 min.) are typical for extrusion operations, diameter in a secondary operation prior to thread Lubricant used while values of 4 mm (160 min.) may be obtained rolling. Condition of the tools using specially designed processes. Constrained forming processes such as cold coining can By an improved method (Fig. 28), the slug was Cold drawing of the wire before cold heading produce Rz510 mm (390 min.). extruded to form two diameters on the shank end,will improve the final surface finish. The best then headed, coined, and trimmed. By this pro-finish on any given workpiece is usually where Combined Heading and Extrusion cedure, the minor extruded diameter was readydirect contact has been made with the tools, such for thread rolling; no turning was required. Theas on the top of a bolt head or on an extruded It is common practice to combine cold heading improved method not only reduced costs byshank portion where cold working is severe. with cold extrusion, and this often permits the eliminating the secondary turning operation but selection of a work metal size that greatly lessens also produced a stronger part, because flow lines The lubricant is likely to have a greater effect forming severity and prolongs tool life. Two were not interrupted at the shoulder.on the appearance of a headed surface than on parts shown in Fig. 15, a trailer-hitch-ball studsurface roughness as measured by instruments. (Fig. 15c) and a center-collar stud (Fig. 15d), Because of the turning operation, productionFor example, heavily limed or stearate-coated reflect the flexibility in design obtained by by the original method was only 300 pieces/h.wire produces a dull finish, but the use of grease combining center upsetting and extrusion. In With the improved method, 3000 pieces could beor oil results in a high-luster finish. addition to increased tool life, other advantages produced per hour. can sometimes be obtained by combining cold The condition of the tools is most important in heading and cold extrusion, as shown in the ±0.13 ±0.13controlling the workpiece finish. Rough surfaces following two examples. ±0.08on punches or dies are registered on the work-piece. Therefore, the best surface finish is pro- Example 7: Combined Heading and Extru- ±0.18 ±0.03 ±0.05duced only from tools that are kept polished. sion That Eliminated Machining. As shown in Fig. 28, lawnmower wheel bolts were originally The ranges of finish shown on the square-necked bolt in Fig. 27 are typical Ra (averageroughness) values for such a part when headedfrom cold-drawn steel, using ground and (a) ±0.08 (b) Fig. 24 Typical tolerances for cold formed parts. (a) Head produced by open heading. (b) Head produced by partial containment in the die. Source: Ref 144 17.40 ± 0.25 7.4 ± 0.1 R 0.4 0.5 1.5 +0.1 φ 12.045° –0.1 φ 7.10 ± 0.05 φ 5.25 ± 0.05 φ 8.45 ± 0.05Fig. 23 (a) Example of a part progression incorporating reverse forming, and (b) the tooling sequence used to create it. Fig. 25 Example of a precision-formed aerospace Courtesy of T. Christoffel, Hatebur Metalforming Equipment, Ltd. fastener using modern cold forming techni- ques. Source: Ref 145

398 / Cold Heading and Cold Extrusion Example 8: Combining Extrusion with was applied as a lubricant when the cold-drawn tool steel heat treated to 67 HRC for highHeading to Decrease Heading Severity. A stock entered the machine for shearing to length. strength and bending resistance.socket-head cap screw was originally producedby heading 23.2 mm (0.915 in.) diameter wire in Example 9: Cold Forming of Gear Blanks Extreme precision is required in the alignmentfour blows, using four dies. By an improved with Close-Tolerance Concentricity. The of the punch and die elements in order to obtainmethod (Fig. 29), the screw was produced by general dimensions of the gear blank are shown the required concentricity. Forming takes placestarting with a larger wire (25.1 mm, or in the drawing (Fig. 30), including the maximum at a rate of 115 parts/min on a four-die cold0.990 in., in diameter) and then combining for- allowed concentricity of 0.05 mm (0.002 in.). former with 3900 kN (440 tonf) forging load andward extrusion with a heading operation in a first The wire is prepared by drawing the rod with a a sequence (Fig. 31) that consists of first hitblow and completing the head by backward 25% area reduction, spheroidize annealing, and upsetting, second hit upsetting and centerextrusion in a second blow. Thus, one die and then a final draw with 5 to 6% area reduction marking, third hit backward extrusion, and hittwo punches replaced four dies and four punches (SAIP). Due to the unfavorable ratio between the fourth piercing. All punches float in o-rings, withfor a reduction in tool cost of approximately inside (ID) and outside (OD) diameters (25%), the second and third station punches being50%. The improved method also permitted the high formability is required in the wire material. guided into the dies with zero clearance. Thispart to be processed in a 3/4-by-8 in. double- This low ratio also leads to increased tool loads zero clearance design provides the necessarystroke header. on the extrusion pin, which can cause bending alignment of the punch before forming the center and potentially increase the concentricity of the mark in the second die and before backward The 25.1 mm (0.990 in.) starting diameter part. The extrusion pin is made from HS 6-5-3-8 extrusion of the ID in the third die (Ref 130).was cold drawn at the header from hot-rolledlime-coated 4037 steel with soap applied for a Example 10: Cold Forming of SAE 52100drawing lubricant. Molybdenum disulfide paste Steel Roller. The roller (Fig. 32) is part of a hydraulic valve-lifter assembly that rotates on a camshaft, thus requiring high hardness (60 to 65 HRC) and wear resistance. The part is made from SAE 52100 SAIP wire (hot rolled, annealed, cold drawn with 25% reduction in area, spheroidize annealed to 90% minimum rating, and final cold 0.115 A 0.103 B 0.095 0.087 1.48 diam 0.755 Dimension A Dimension B 30 49 piecesNumber of pieces 100 Lot 1 20 pieces 10 Lot 2 50 pieces 8 11–6–1 0 30 50 20 piecesNumber of pieces 10 0.990 0.915 8 diam 0 Lot 3 50 pieces Wire diam 30 slug First blow: Headed Second blow: 50 20 pieces and forward extruded Backward extruded 10 Fig. 29 Production of a large 4037 steel cap screw by 0 0.105 0.090 0.095 0.100 0.105 extruding and heading in two blows. Dimen- 0.100 Measured dimension, in. sions given in inchesFig. 26 Variations in dimensions of 1010 steel valve- Ø 26.0 spring retainers randomly selected from three 0.05lots. Parts were produced in a five-station nut former.Dimensions given in inches 4 to 32 8 to 32 8 to 32 2263 to 12516 to 63 16 to 638 to 32 32 to 63 Ø 13.0Fig. 27 Typical variations in surface roughness at Fig. 28 Combined extrusion and cold heading used to Fig. 30 Cold formed gear blank with close-tolerance various locations on a square-necked bolt reduce production costs for a 1018 steel concentricity requirement. Courtesy of M. vanheaded from cold-drawn steel with ground and polished lawnmower wheel. A turning operation was eliminated by Thiel, Nedschroef Herentals N.V.tools. Roughness given in microinches cold extruding the diameter to be roll threaded. Dimen- sions given in inches

Cold Heading / 399 Ø10.15 ±0.05 0.05 A A 0.5R max 0.05 AT 12.70 ±0.05 8.62 min 1.83 min Ø14.0 ±0.25 Ø18.03 ±0.05 0.05 A 0.00.055 AA Fig. 32 Cold formed roller with close-tolerance requirements. Courtesy of M. van Thiel, Nedschroef Herentals N.V.Fig. 31 Tooling layout for cold forming precision gear blanks. Courtesy of M. van Thiel, Nedschroef Herentals N.V. squaring. The second hit is another long extru- sion combined with a bulbing operation to gather Piercing material prior to the third hit upset that forms most of the head shape. The final operation fin-Ø10.56 Ø18 Ø17.95 Ø14.8 Ø14.5 –0.04 ishes the head shape. The forging load is sub- stantially reduced in the last station, because only the outer portion of the head requires forming. The tool layout (Fig. 37) shows the long strokes that are required to form this part, which require careful guiding and support of the die kickout pins to prevent bending. All forming takes place completely in the dies, with the very top of the bulb in the second hit being contained in a die cavity within the punch case. Warm Heading 13.2 In warm heading (a variation of the cold- heading process), the work metal is heated to a 12.85 13.0 10.6 13.6 temperature high enough to increase its ductilityØ13.95 yet still below the recrystallization temperature. A rise in work metal temperature usually resultsFig. 33 Roller part progression demonstrating 180 transfer from the first die to the second die, and straight-across in a marked reduction in the energy required for heading the material, with tooling loads reduced transfers for the rest of the dies. Courtesy of M. van Thiel, Nedschroef Herentals N.V. by as much as 50% compared to cold forming. These lower tool forces generally reduce diedrawing with 5% reduction in area) with a tensile forming operations (second, third, and fifth hits) breakage, but the higher contact temperaturesstrength of 650 to 700 MPa (94 to 102 ksi). SAE use zero clearance to achieve the necessary can result in increased wear. Temperatures for52100 is very difficult to cold form due to its concentricity, perpendicularity, and cylindricity. warm heading typically range from 175 tochemical composition (1% C, 1.5% Cr) and Due to the high strength and work hardening of 650 C (350 to 1200 F) but may be as high asattendant microstructure and often is warm 52100, the punches are all TiN-coated HS 6-5-3 approximately 980 C (1800 F), depending onformed in order to improve formability and tool steel, while the third hit kickout pin is a the characteristics of the work metal.reduce tool stresses. In some instances, it is 7%Co-WC. The end result is a cold formed blanknecessary to have the surface peeled in order to that was previously only able to be produced as a Applications. Warm heading is occasionallyremove any defects that would impair form- fully machined part and only requires a light final used to produce an upset that would haveability. ID/OD grind to meet the final requirements. required a larger machine if the upsetting were done cold, but by far the most extensive use of The part is cold formed at a rate of 250 parts/ Example 11: Cold Forming of Automotive warm heading is for the processing of difficult-min on a five-die nut former with 2100 kN Engine Intake Valve. The valve (Fig. 35) is to-head metals, such as stainless steels, titanium(236 tonf) forging load, using the progression normally hot forged, because the large diameter alloys, and nickel-base alloys. Typical examplesshown in Fig. 33. The first hit squares up the ratio between the shaft and the head causes include the manufacture of high-strength fas-blank and marks both sides. The part is then cracks to occur in the head during cold defor- teners from alloys such as A-286, Ti-6Al-4V,rotated 180 during transfer to the second die, mation. Successful cold forming of the marten- and alloy 718, as well as inner and outer bearingwhere the blank is fully contained in the die and sitic valve steel grade (UNS S65007, X45CrSi races using martensitic stainless steels. Warmupset on both sides. The third hit is a combination 9 3) was achieved by using SAIP wire (hot rolled, heading allows for high-speed production offorward-backward extrusion, followed by pier- annealed, cold drawn with 25% reduction in parts that would otherwise have to be forged oncing of the ID in the fourth hit. The last operation area, spheroidize annealed to 90% minimum vertical presses, often eliminating the need forsizes the ID as well as mildly upsets the entire rating, and final cold drawing with 5% reduction reheating and relubricating the workpiece.blank to fill out the external corners. in area). The part progression (Fig. 36) shows a long forward extrusion as the first operation, The data shown in Fig. 38 suggest that The tool layout (Fig. 34) shows that all of the because the precise cutoff blank did not require the speed of the heading punch greatly affectspunches after the first hit are floating, and that the

400 / Cold Heading and Cold Extrusionthe headability of austenitic stainless steels. tion heating coils or resistance heating elements Temperature Control. Close control of wireAccording to investigations, 80% of the loss in can be used as auxiliary heating equipment. surface and core temperature is important,ductility caused by heading speed can be Vertical presses can also be used for elevated- because uneven heating causes variable tem-recovered if the metal is heated to between 175 temperature heading operations but are most perature distribution and therefore variableand 290 C (350 and 550 F). The increase in often used on large-diameter parts that are hot deformation resistance. This results in poorheadability with increasing temperature is indi- headed, meaning above the recrystallization workability and difficulty in maintainingcated in Fig. 39. When temperatures increase to temperature. dimensional capability. Also, the lubricity of thethe upper end of the warm heading range, how- wire coating may be altered, with the coatingever, there is a tendency for slug buckling to Induction heating is the method most com- smearing onto the tooling at the cutoff stationoccur during upsetting, due to the reduction in monly used to heat work material for warm and impairing subsequent formability.column strength. Because they work harden heading, although direct resistance heating israpidly, these alloys are best headed at slow ram also used in some applications. The wire is Tools. Whether or not the same tools can bespeeds of approximately 60 to 100 strokes/min usually heated before it enters the feed rolls, but used for warm heading as for cold heading(approximately 10 to 15 m/min). it is advantageous to use a setup with the depends entirely on the temperature of the tools induction coil between the feed rolls and the during operation. Although the tools usually Warm heading is especially useful for forming header machine frame. The main drawback of operate at a temperature considerably lower thantitanium alloys, due to the limited cold ductility induction heating is the high initial cost of the that of the work metal, it is important that the toolof alpha-beta alloys and the high yield strength power supply. Therefore, its use is generally temperature be known. Tool temperature can beof all alloys in the annealed condition. Heating restricted to continuous high production. checked with sufficient accuracy by means ofto a temperature of 430 C (800 F) results in temperature-sensitive crayons. Under no cir-approximately a 40% reduction in yield strength Direct resistance heating, on the other hand, cumstances should the tool be allowed to exceed(Ref 146). Warm forming of relatively simple has the advantages of simplicity of equipment, the temperature at which it was tempered aftershapes can be performed in the range of 430 to accuracy of control, safety (because voltage is hardening. Tools such as die inserts made from a590 C (800 to 1100 F), with more complicated low), and adaptability to heating of a continuous high-alloy tool steel, such as D2, ordinarilyshapes being headed in the range of 650 to length of work metal. The usual setup for resis- should not be permitted to operate above 260 C850 C (1200 to 1560 F) (Ref 147–149). Tita- tance heating employs a second feeder-roll stand (500 F).nium alloys are very sensitive to heading speed similar to that already on the header. The secondand readily form adiabatic shear bands at high stand is positioned approximately 1.5 m (5 ft) When tool temperatures exceed those dis-strain rates. behind the first, and the wire stock (work metal) cussed previously, the use of tools made from a is fed through both sets of rolls. Leads from the Machines and Heating Devices. Warm- electrical equipment are attached to the two sets Ø 27.6 0heading machines are essentially the same as of rolls, and the circuit is completed by the por- –0.2cold-heading machines, except that warm- tion of the wire that passes between them. Theheading machines are designed to withstand the wire (work metal) then becomes the resistance Ø 24.1 0elevated temperature of the work metal. Induc- heater in the circuit. –0.2 R30 ref Ø 23.1 0 45°Ϯ2° No burr –0.2 R1Ϯ0.5 +0.25 Ø 20.95Ϯ1 25°Ϯ2° 0 +0.25 2.90 0 1.15 15.5 min R5Ϯ1 1.9Ϯ0.15 Ø 6.85 max 115 +2 0 Ø 6.5 0 – 0.2Fig. 34 Tooling layout for cold forming precision roller. Courtesy of M. van Thiel, Nedschroef Herentals N.V. Fig. 35 Cold formed engine intake valve. Courtesy of M. van Thiel, Nedschroef Herentals N.V.

Cold Heading / 401 Ø 27.5 Ø 26.0 Ø 18.8 Ø 12.5 3.0 22.5 45.8 Type 302 Heading limit (D2/D1) 97.4 Cutoff stainless steel 2.5 Type 316 3.1 Ø 12.7 2.0 Ø 24 100.7 1038 steel 1.5 Type 310116.0 D1 = Original diameter D2 = Headed diameter 105.9 1.0 100 102 104 106 10–2 Heading speed, in. per min Fig. 38 Effect of heading speed on heading limits for three austenitic stainless steels and for 1038 steel Ø 6.35 Ø 6.4 Temperature, °F 200 300 Ø 7.3 100 400 3.0Fig. 36 Part progression for cold forming engine intake valve. Courtesy of M. van Thiel, Nedschroef Herentals N.V. Heading limit, D2/D1 2.5 D1, original diameter 2.0 D2, headed diameter 1.5 Heading speed: 400 in./min 1.0 50 100 150 200 250 0 Temperature, °C Fig. 39 Effect of work metal temperature on heading limit of austenitic stainless steel Hardness, HRC Temperature, °F 100 200 300 400 40 30 Finished head 20 Upset 10 0 0 50 100 150 200 250 Temperature, °C Fig. 40 Effect of heading temperature on the hardness of the upset portion and finished head of type 305 stainless steel flat-head machine screwsFig. 37 Tooling layout for cold forming engine intake valve. Courtesy of M. van Thiel, Nedschroef Herentals N.V. decreases, as shown in Fig. 40. Therefore, if a material is warm headed, the hardness willhot-work tool steel, such as H12 or H13, is for long tool life. Standard grades for recessed remain low enough to permit such secondaryappropriate. However, the lower maximum punches include M1 and M2, with advanced operations as thread rolling, trimming, drilling,hardness of such a steel somewhat limits its tooling materials such as P/M M4, T15, and A11 and slotting.resistance to wear. More typical is the use of being used when conditions warrant.high-speed tool steels such as M2 or M4 (60 to 63 In cold heading, the upset head of a work-HRC) for die inserts, which provide the high Other Advantages of Warm Heading. As hardening metal is very hard, a rolled thread ishardness and the resistance to tempering needed the heading temperature of a work-hardenable moderately hard, and the undeformed shoulder is material increases, the resulting hardness relatively soft. These variations can be mini- mized by warm heading.

402 / Cold Heading and Cold ExtrusionACKNOWLEDGMENTS Mater. Sci. Forum, Vol 449–452, 2004, 31. H. Ko¨hler, High Strength Fasteners Made p 105–108 of Dual-Phase Steel without Quenching The authors would like to express their sin- 14. J. Domblesky, “Using a Process Model to and Tempering, ATZ World., Vol 100cerest appreciation to the following individuals Analyze Die Stresses on a Desktop PC,” (No. 10), 1998for generously contributing information and SME Technical Paper MF97–137, Societyimages to this article: Jerry Bupp of National of Manufacturing Engineers 32. W. Cook et al., Cold Forging for HighMachinery, Steve Buzolits of SPS Technologies, 15. L. Monroe, Net Shape Cold Forming, Strength Lower Cost Steel Fasteners,Thomas Christoffel of Hatebur Equipment, Fasten. Technol. Int., Dec. 1999, p 40–42 Ironmaking Steelmaking, Vol 22 (No. 2),Frauke Hogue of Hogue Metallography, Cory 16. D. Hannan et al., Case Studies on 1995, p 117–131Padfield of Hyundai America, Richard Perlick of Improving the Tool Life of Cold HeadingTechalloy Company, and Marc van Thiel of Operations, Fasten. Technol. Int., Aug 33. D. Goss, High Strength Fasteners ColdNedschroef-Herentals. Also, the authors are 2000, p 56–60 Forged out of Work Hardening Steel,extremely grateful for the considerable assis- 17. C. MacCormack, 2-D and 3-D Finite Ele- J. Mater. Process. Technol., Vol 98, 2000,tance with graphics, the thorough review, and the ment Analysis of a Three Stage Forging p 135–142helpful discussions provided by Cory Padfield Sequence, J. Mater. Process. Technol., Volduring this project. 127, 2002, p 48–56 34. P. Wanjara et al., Dual-Phase Steels for 18. J. Walters, Metal Forming Computer Cold-Heading Applications, Wire J. Int.,REFERENCES Simulation Optimizes Fastener Manu- Vol 34 (No. 9), 2001, p 104–107 facturing, Fasten. Technol. Int., Aug 2003, 1. “Upsetting,” technical brochure, National p 22–24 35. “Mechanische Eigenschaften von Verbin- Machinery Co., Tiffin, OH, 1971, p 11 19. J. Walters, Troubleshooting Cold Heading dungselementen der Festigkeitsklasse 800 Die Failures, Wire J. Int., Vol 37 (No. 1), K” (Mechanical Properties of Fasteners 2. K. Carlson, “The Cold-Heading Process,” 2004, p 62–66 of Property Class 800 K), VDA 235-202, SME Technical Paper MF70-110, Society 20. G. Smith et al., “Cold Forming Machin- Verband der Automobilindustrie, Oct 2001 of Manufacturing Engineers ery,” Cold Forming 101 Technical Semi- (in German) nar, Fastener Technology International, 3. Cold and Warm Upsetting (Heading), 2004 36. “Standard Specification for Stainless Steel Forming, Vol 2, Tool and Manufacturing 21. “Standard Specification for Quality Wire and Wire Rods for Cold Heading and Engineers Handbook, Society of Manu- Assurance Requirements for Carbon and Cold Forging,” A 493-95, ASTM Interna- facturing Engineers, 1988, p 13-42 to Alloy Steel Wire, Rods, and Bars for tional, 2000 13-56 Mechanical Fasteners,” F 2282-03, ASTM International 37. “Steel Rod, Bars and Wire for Cold 4. “Forging Machine Die Design,” Item 22. “Standard Specification for General Heading and Cold Extrusion, Part 5: 278B, National Machinery Co., Tiffin, OH Requirements for Wire Rods and Coarse Technical Delivery Conditions for Stain- Round Wire, Carbon Steel,” A 510-03, less Steels,” EN 10263-5, European Com- 5. M. Go¨kler et al., Analysis of Tapered Pre- ASTM International mittee for Standardization forms in Cold Upsetting, Int. J. Mach. 23. “Steels for Cold Heading and Cold Tools Manuf., Vol 39, 1999, 1–16 Extruding,” ISO 4954, International 38. “Stainless Steel Wires for Cold Heading Organization for Standardization and Cold Forging,” JIS G4315-2000, 6. “Tool Design and Part Shape Development 24. “Steel Rod, Bars and Wire for Cold Japanese Standards Association for Multi-Die Cold Forming,” Item 743A, Heading and Cold Extrusion, Part 2: National Machinery Co., Tiffin, OH Technical Delivery Conditions for Steels 39. V. Moiseev, High-Strength Titanium Alloy Not Intended for Heat Treatment after Cold VT16 for Manufacturing Fasteners by the 7. K. Sevenler et al., Forming-Sequence Working,” EN 10263-2, European Com- Method of Cold Deformation, Met. Sci. Design for Multistage Cold Forging, mittee for Standardization Heat Treat. (Russia), Vol 44 (No. 5–6), J. Mech. Work. Technol., Vol 14, 1987, 25. “Steel Rod, Bars and Wire for Cold 2002, p 194–197 121–135 Heading and Cold Extrusion, Part 3: Technical Delivery Conditions for Case 40. V. Volodin et al., Manufacture of Fasteners 8. H. Kim et al., Computer-Aided Part and Hardening Steels,” EN 10263-3, European and Other Items in Titanium Alloys, Processing-Sequence Design in Cold For- Committee for Standardization Advances in the Science and Technology of ging, J. Mater. Process. Technol., Vol 33, 26. “Steel Rod, Bars and Wire for Cold Titanium Alloy Processing, TMS, 1997, 1992, p 57–74 Heading and Cold Extrusion, Part 4: Tech- p 319–330 nical Delivery Conditions for Steels for 9. H.-S. Kim et al., Expert System for Multi- Quenching and Tempering,” EN 10263-4, 41. G. Turlach, Ultra-High Strength Bolts Stage Cold-Forging Process Design with European Committee for Standardization Made from Beta-C-Alloy Titanium, Tita- a Re-Designing Algorithm, J. Mater. Pro- 27. “Carbon Steel Wire Rods for Cold Heading nium ‘95: Science and Technology, Pro- cess. Technol., Vol 54, 1995, p 271–285 and Cold Forging,” JIS G3507-1991, ceedings, Eighth World Conference on Japanese Standards Association Titanium, Vol 2, 22–26 Oct 1995 (Bir- 10. M. Kim et al., An Automated Process 28. “Low-Alloyed Steels for Cold Heading, mingham), 1996, p 1625–1637 Planning and Die Design System for Part 1: Wire Rods,” JIS G3509-1: 2003, Quasi-Axisymmetric Cold Forging Pro- Japanese Standards Association 42. “American National Standard for Alloy ducts, Int. J. Adv. Manuf. Technol., Vol 20, 29. “Low-Alloyed Steels for Cold Heading, and Temper Designation Systems for 2002, p 201–213 Part 1: Wire,” JIS G3509-2: 2003, Japanese Aluminum,” ANSI H35.2, American Standards Association National Standards Institute 11. I. Duplancic et al., Case Studies on Process 30. “Carbon Steel Wires for Cold Heading and Sequence Design in Cold Forming of Cold Forging,” JIS G3539-1991, Japanese 43. “Standard Specification for Copper-Silicon Engine Valve Slider and Self-Locking Standards Association Alloy Wire for General Applications,” Nuts, Int. J. Mach. Tools Manufact., Vol 34 B 99/B 99M-01, ASTM International (No. 6), 1994, p 817–828 44. “Standard Specification for Brass 12. H. Kim et al., Cold Forging of Steel— Wire,” B 134/B 134M-01, ASTM Inter- Practical Examples of Computerized Part national and Process Design, J. Mater. Process. Technol., Vol 59, 1996, p 122–131 45. “Standard Specification for Aluminum and Aluminum-Alloy Rivet and Cold-Heading 13. H. Choi et al., A Study on the Process Wire and Rods,” B 316/B 316M-02, ASTM Design of Cold-Forged Automobile Parts, International 46. K. Downs, Jr., “Aluminum Use in Fastener Manufacturing,” SME Technical Paper EM87-735, Society of Manufacturing Engineers

Cold Heading / 40347. “Steel Rod, Bars and Wire for Cold Mater. Sci. Forum, Vol 426–432, 2003, 81. Heading Hints: A Guide to Cold Forming Heading and Cold Extrusion, Part 1: Gen- p 4447–4454 Specialty Alloys, Carpenter Technology eral Technical Delivery Conditions,” EN 64. M. Shabara et al., Validity Assessment of Corporation, 2001 10263-1, European Committee for Stan- Ductile Fracture Criteria in Cold Forming, dardization J. Mater. Eng. Perform., Vol 5 (No. 4), 82. A. Echtenkamp, “Use and Abuse of Car- 1996, p 478–488 bide Tooling for Cold Forming,” SME48. S. Chattopadhyay et al., Quantitative 65. “Lubrication Aspects in Cold Forging of Technical Paper MR90-298, Society of Measurements of Pearlite Spheroidi- Aluminium and Aluminium Alloys,” ICFG Manufacturing Engineers zation, Metallography, Vol 10, 1997, Document 10/95, International Cold For- p 89–105 ging Group, 1995 83. Die and Mold Materials, Forming, Vol 2, 66. “Beschichten von Werkzeugen der Kalt- Tool and Manufacturing Engineers Hand-49. T. Das, Evaluation of Two AISI 4037 Cold massivumformung CVD- und PVD-Ver- book, Society of Manufacturing Engineers, Heading Quality Steel Wires for Improved fahren [Coating (CVD, PVD) of Cold 1984, p 2-1 to 2-30 Tool Life and Product Quality, J. Mater. Forging Tools],” VDI 3138, VDI, Aug Eng. Perform., Vol 11 (No. 1), 2002, 1982 (in German) 84. T. Arai, Tool Materials and Surface p 86–91 67. U. Bonde, “Modern Tool Design,” SME Treatments, J. Mater. Process. Technol., Technical Paper MF97-135, Society of Vol. 35, 1992, p 515–52850. M. Kaiso et al., Cold Forgeability in Manufacturing Engineers Medium Carbon Steel with Insufficiently 68. U. Bonde, “Design of Cold Forming Tools 85. E. Tarney, “Selecting High Performance Spheroidized Microstructure, Tetsu-to- Based on Practical Experiences,” SME Tool Steels for Cold Forming Applica- Hagane (J. Iron Steel Inst. Jpn.), Vol 84 Technical Paper MF90-297, Society of tions,” SME Technical Paper MF97-201, (No. 10), 1998, p 721–726 Manufacturing Engineers Society of Manufacturing Engineers 69. U. Bonde, “Holding Close Tolerances on51. X. Ma et al., Effect of Microstructure on Coldformed Parts,” SME Technical Paper 86. R. Carnes et al., Tool Steel Selection, Adv. the Cold Headability of a Medium Carbon MF92-138, Society of Manufacturing Mater. Process., June 2004, p 37–40 Steel, ISIJ Int., Vol 44 (No. 4), 2004, Engineers p 905–913 70. F. Hobrath, “Design of Tooling for High 87. T. Hillskog, Powder-Metallurgy Tool Pressure Cold Forming,” SME Technical Steels: An Overview, Met. Form., Jan52. D. Hernandez-Silva et al., The Spher- Paper TE87-443, Society of Manufacturing 2003, p 48–51 oidization of Cementite in a Medium Car- Engineers bon Steel by Means of Subcritical and 71. “Calculation Methods for Cold Forging 88. T. Schade, Matrix High-Speed Steels: Intercritical Annealing, ISIJ Int., Vol 32 Tools,” ICFG Document 5/82, Interna- Economical Alternative to Powders, Met. (No. 12), 1992, p 1297–1305 tional Cold Forging Group, 1982 Form., May 2004, p 48–50 72. “General Recommendations for Design,53. G. Krauss, Solidification, Segregation, and Manufacture, and Operational Aspects of 89. M. McCabe, “How PVD Coating Can Banding in Carbon and Alloy Steels, Cold Extrusion Tools for Steel Compo- Increase Your Productivity and Effi- Metall. Mater. Trans. B, Vol 34, 2003, nents,” ICFG Document 6/82, Interna- ciency,” Cold Forming 2001 Technology p 781–792 tional Cold Forging Group, 1982 Conference, Society of Manufacturing 73. Automatic Cold and Warm Forming, Engineers54. N. Muzak et al., New Methods for Asses- Forming, Vol 2, Tool and Manufacturing sing Cold Heading Quality, Wire J. Int., Engineers Handbook, Society of Manufac- 90. Y. Lee et al., Failure Analysis of Cold- Vol 29 (No. 10), 1996, p 66–72 turing Engineers, 1988, p 13–57 to 13–63 Extrusion Punch to Enhance Its Quality 74. “Standard Specification for Tool Steels, and Prolong Its Life, J. Mater. Process.55. R. Thibau et al., Development of a Test High Speed,” A 600-92a, ASTM Interna- Technol., Vol 105, 2000, p 134–142 to Evaluate the Formability of CHQ tional, 2004 Wire, Wire J. Int., Vol 33 (No. 2), 2000, 75. “Standard Specification for Tool Steels, 91. M. Geiger, Fatigue of PVD and CVD p 146–154 Alloy,” A 681-94, ASTM International, Coated Tool Steel for Cold Forging, Wire, 2004 Vol 47 (No. 6), p 30–3356. J. Dhers et al., Improvement of Steel Wire 76. “Standard Specification for Tool Steels, for Cold Heading, Wire J. Int., Vol 25 Carbon,” A 686-92, ASTM International, 92. B. Jakicic et al., STC Batch Furnace Offers (No. 10), 1992, p 73–76 2004 Production Flexibility, Ind. Heat., March 77. “Tool Steels,” ISO 4957, International 200157. R. Kienreich et al., Improved Cold Form- Organization for Standardization ability by Thermo-Mechanical Rod Roll- 78. “General Aspects of Tool Design and Tool 93. J. O’Brien et al., Spheroidizing of Medium ing, Steel Res., Vol 74 (No. 5), 2003, Materials for Cold and Warm Forging,” Carbon Steels, Ind. Heat., Sept 2000, p 304–310 ICFG Document 4/82, International Cold p 79–84 Forging Group, 198258. H. Hata et al., Development of High 79. A. Bayer et al., Wrought Tool Steels, 94. J. O’Brien et al., Spheroidizing Cycles Quality Wire Rod through Thermo- Properties and Selection: Irons, Steels, and of Medium Carbon Steels, Metall. mechanical Control Processes, Kobelco High-Performance Alloys, Vol 1, ASM Mater. Trans. A, Vol 33, April 2002, Technol. Rev., No. 25, April 2002, p 25–29 Handbook, ASM International, 1990, p 1255–1261 p 757–77959. T. Ochi et al., Special Steel Bars and Wire 80. K. Pinnow et al., P/M Tool Steels, Prop- 95. D. Hughes, The Heat Treatment of Rods Contribute to Eliminate Manu- erties and Selection: Irons, Steels, and Ferrous Fasteners, Surface Combustion, facturing Processes for Mechanical Parts, High-Performance Alloys, Vol 1, ASM Inc., 1999 Nippon Steel Tech. Rep., No. 80, July 1999, Handbook, ASM International, 1990, p 9–15 p 780–792 96. F. Pere et al., Wire and Rod Coil Spher- oidising Annealing Furnaces, EuroWire60. “Cold-Heading Wire,” Fagersta Stainless Mag., July 2004 AB, April 2000 97. K. Naidu et al., Quality Annealing Eco-61. K. Downs, Jr. “Annealing and Heat Treat- nomically, Wire J. Int., Vol 16 (No. 5), ment of Aluminum Wire,” SME Technical 1983, p 66–73 Paper MF88-191, Society of Manufactur- ing Engineers 98. R. Draker et al., Control of Surface Carbon during Intercritical and Subcritical62. S. Narayana Murty et al., Improved Ductile Annealing, Wire J. Int., Vol 33 (No. 1), Criterion for Cold Forming of Spher- 2000, p 96–103 oidized Steel, J. Mater. Process. Technol., Vol 147, 2004, p 94–101 99. “Heat Treatment Wrought Aluminum Alloy Parts,” SAE AMS2770, SAE Inter-63. C. El-Lahham et al., Formability national Criteria for Cold Heading Applications, 100. Heat Treater’s Guide: Practices and Pro- cedures for Irons and Steels, 2nd ed., ASM International, 1995

404 / Cold Heading and Cold Extrusion101. Heat Treater’s Guide: Practices and Pro- 117. R. Guthrie, “Reducing Raw Material Costs 133. S. Schmid et al., Tribology in Manufactur- cedures for Nonferrous Alloys, ASM and Handling,” SME Technical Paper ing, Chapter 37, Modern Tribology Hand- International, 1996 AD83-850, Society of Manufacturing book, CRC Press LLC, 2001 Engineers102. “Heat Treatment Precipitation-Hardening 134. H. Dwuletzki, Chlorine-Free Cold Form- Corrosion-Resistant and Maraging Steel 118. Z. Zimerman, Making Quality Steel Wire ing, Fasten. Technol. Int., Dec 2000 Parts,” SAE AMS2759/3C, SAE Interna- at Optimum Productivity, Wire J. Int., Vol tional 21 (No. 8), 1988, p 50–58 135. “Lubrication Aspects in Cold Forging of Carbon Steels and Low Alloys Steels,”103. “Heat Treatment Wrought Nickel Alloy 119. A. Karimi Taheri, Dynamic Strain Aging ICFG Document 8/91, International Cold and Cobalt Alloy Parts,” SAE AMS2774, and the Wire Drawing of Low Carbon Steel Forging Group, 1991 SAE International Rods, ISIJ Int., Vol 35 (No. 12), 1995, p 1532–1540 136. S. Savage et al., Investigation into Cold104. “Heat Treatment of Titanium Alloy Parts,” Heading Lubricants, Metal Forming 2000, SAE AMS2801, SAE International 120. R. Sherman et al., Method of Forming a M. Pietrzyk et al., Ed., (Belkema, Rotter- Fastener, U.S. Patent 6,017,274 dam), Institute for Metal Forming, 2000,105. “Standard Specification for General p 569–575 Requirements for Stainless Steel Wire and 121. R. Shemenski, Wiredrawing by Computer Wire Rods,” A 555/A 555M-97, ASTM Simulation, Wire J. Int., Vol 32 (No. 4), 137. Fabricating, Special Metals Corporation, International, 2002 1999, p 166–183 Huntington, WV106. “Steel Wire and Wire Products—Gen- 122. R. Wright, “Factors to Consider in Wire 138. D. Dallas, “Secondary Upsetting—A eral—Part 2: Wire Dimensions and Toler- Die and Pass Schedule Design,” SME New Concept in Cold Header Tooling,” ances,” EN 10218-2, European Committee Technical Paper MF77-960, Society of Item 642A, National Machinery Co., for Standardization Manufacturing Engineers Tiffin, OH107. “Aluminum and Aluminum Alloys— 123. T. Maxwell, “Seven Parts of a Carbide 139. “Advanced Cold Forming Principles,” Drawn Wire—Part 3: Tolerances on Die,” Cold Forming 2001 Technology Item 7049A, National Machinery Co., Dimensions,” EN 1301-3, European Conference, Society of Manufacturing Tiffin, OH Committee for Standardization Engineers 140. T. Hay, Multiple-Axis Forming Applica-108. “American National Standard Dimensional 124. B. Avitzur et al., Metal Working: Drawing tions, Fasten. Technol. Int., Feb 2003, Tolerances for Aluminum Mill Products,” of Bars and Wires, Encyclopedia of Mate- p 30–31 ANSI H35.2-1993, American National rials: Science and Technology, Elsevier Standards Institute Science Ltd., 2001 141. J. Bupp, Blank Rotator Offers New Tool- ing Solutions, Fasten. Technol. Int., Aug109. “Tolerances, Metric, Corrosion and Heat 125. D. Hohman, “Alcoa-Massena Operations: 2003, p 34–35 Resistant Steel, Iron Alloy, Titanium, and An Integrated Aluminum Aerospace For- Titanium Alloy Bars and Wire,” SAE ging Stock Provider,” SAE Technical 142. R. Schilling et al., “Advancements in Net MAM2241, SAE International Paper 912132, SAE International, 1991 Shape Cold-Forming,” SME Technical Paper MF97-134, Society of Manufactur-110. “Tolerances, Metric, Nickel, Nickel 126. L. Lemoine et al., Experimenting with the ing Engineers Alloy, and Cobalt Alloy Bars, Rods, Latest Pickling Technologies, Wire J. Int., and Wire,” SAE MAM2261, SAE Inter- Vol 36 (No. 11), 2003, p 64–66 143. M. Shutt, “Cold Forming for Precision national and Economy,” SME Technical Paper 127. J. Stone, “Descaling of Carbon Steel MF82-345, Society of Manufacturing111. H. Kushida et al., Sizing Roll Tech- Rod and Wire,” SME Technical Paper Engineers nology for Closed-Tolerance Wire Rod, MF88-195, Society of Manufacturing Kobelco Technol. Rev., No. 25, April 2002, Engineers 144. R. Jordt, The Manufacture and Application p 21–24 of Fasteners, Technifast Industries, Inc., 128. “Cropping of Steel Bar—Its Mechanism June 2001112. R. Takeda et al., “Close-Tolerance Bars and Practice,” ICFG Document 3/82, and Wire Rods,” Kawasaki Technical International Cold Forging Group, 1982 145. M. Lucius, “Realities of Quick Change,” Report 26, June 1992, p 87–89 SME Technical Paper MF90-299, Society 129. J. Pennington, High-Energy Process Cuts of Manufacturing Engineers113. Y. Noguchi et al., “Characteristics of Con- Long Products, Mod. Met., May 2003 tinuous Wire Rod Rolling and Precision 146. “Alloy Data, Titanium Alloy Ti 6-Al-4V,” Rolling System,” Nippon Steel Technical 130. M. van Thiel, Cold Forming of Gear Dynamet Holdings Inc., July 2000 Report 80, July 1999, p 79–83 Blanks with Close-Tolerance Con- centricity, Fasten. Technol. Int., April 147. N. Heil et al., Method and Apparatus for114. D. Diorio, “Interface between Wire Pro- 2003, p 76–77 Producing Fasteners Having Wrenching ducer and Cold Heading Quality User,” Sockets Therein, U.S. Patent 4,805,437, SME Technical Paper MF87-455, Society 131. N. Bay, Metal Forming and Lubrication, 1989 of Manufacturing Engineers Encyclopedia of Materials: Science and Technology, Elsevier Science Ltd., 148. J. Arnosky et al., “Induction Heating for115. R. Perlick, Exotic Alloys for Fasteners and 2001 Warm Heading,” SME Technical Paper Cold Forming, Fasten. Technol. Int., April AD83-854, Society of Manufacturing 2001, p 33–36 132. I. Tripp, “Cold Heading and Extrusion Engineers Lubricants: A Primer on Testing Techni-116. M. van Thiel, Material Feeding in Large- ques and Process Controls,” SME Techni- 149. D. Stoppoloni, “New Titanium Alloys for Diameter Cold Forming Operations, Fas- cal Paper AD85-1040, Society of Fastener Applications in F1 engines,” ten. Technol. Int., Oct 2004, p 33–36 Manufacturing Engineers Third Aluminium Days International Symposium, Nov 2003