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Manufacturing Processes > Forming Processes > Cold Heading

 

Cold Heading

 

Process description

Wire form stock material is gripped in a die with usually one end protruding. The material is subsequently formed (effectively upset) by successive blows into the desired shape by a punch or a number of progressive punches. Shaping of the shank can be achieved simultaneously.

Materials

  • Suitable for all ductile metals: principally, carbon steels, aluminum, copper and lead alloys.
  • Alloy and stainless steels, zinc, magnesium, nickel alloys and precious metals are also processed.
Cold Heading

Process variations

  • Usually performed with stock material at ambient temperature (cold), but also with stock material warm or hot.
  • Solid die: single stroke, double stroke, three blow, two die, progressive bolt makers, cold or hot formers – the choice is determined by the length to diameter ratio of the raw material.
  • Open die: parts made by this process have wide limits and are too long for solid dies.
  • Continuous rod or cut lengths of material can be supplied to the dies.
  • Can incorporate other forming processes, for example: knurling, thread rolling and bending to produce complex parts at one machine.
  • Upset forging: heated metal stock gripped by dies and end pressed into desired shape, i.e. increasing the diameter by reducing height.

Economic considerations

  • Production rates between 35 and 120/min common.
  • Lead times relatively short due to simple dies.
  • High material utilization. Virtually no waste.
  • Flexibility moderate. Tooling tends to be dedicated.
  • Production quantities typically very high, 100 000+, but can be as low as 10 000.
  • Tooling costs moderate.
  • Equipment costs moderate.
  • Direct labor costs low. Process highly automated.
  • Finishing costs low: normally no finishing is required.

Typical applications

  • Electronic components
  • Electrical contacts
  • Nails
  • Bolts and screws
  • Pins
  • Small shafts

Design aspects

  • Complexity limited to simple cylindrical forms with high degree of symmetry.
  • Significant asymmetry difficult.
  • Minimization of shank diameter and upset volume important.
  • Radii should be as generous as possible.
  • Threads on fasteners should be rolled wherever possible.
  • Head volumes limited due to amount of deformation possible.
  • Inserts possible at added cost.
  • Undercuts produced via secondary operations.
  • Machining usually not required.
  • Draft angles not required.
  • Minimum diameter =Ø0.8 mm.
  • Maximum diameter =Ø50 mm.
  • Minimum length =1.5 m.
  • Maximum length =250 mm.

Quality issues

  • Cold working process gives improved mechanical properties.
  • Fatigue, impact and surface strength increased giving a tough, ductile, crack resistance structure.
  • Small quantities of sulfur, lead, phosphorus, silicon, etc. reduce the ability of ferrous metals to withstand cold working.
  • Length to diameter ratio of protruding shank to be formed should be below 2:1 to avoid buckling.
  • Residual stresses may be left at critical points.
  • Sharp corners reduce tool life.
  • Surface detail is good to excellent.
  • Surface roughness ranging 0.8–6.3 µm Ra.
  • Process capability charts showing the achievable dimensional tolerances for cold heading are provided.

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