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Lesson 3.5DeformChapter 3 · Bulk forming

Cold heading

Cut wire into blanks and punch a head, cold

Cold heading cuts a short piece of wire and hammers one end into a head, at room temperature, in a fraction of a second. Almost every screw, bolt, nail and rivet you own was made this way. It wastes almost no metal and is one of the fastest ways to make a solid part.

Cold heading: a real photo
Photo: R. Henrik Nilsson, CC BY 4.0, via Wikimedia Commons
Cold wire is cut and punched into a head in a few blows, with no heat and no chipsOne machine moves each blank through several stations; a fast header makes hundreds of parts a minute.1Cut a blank2Upset (1st blow)3Form the head4Eject the blankfeed tubewireblankcutterwire fed indiepunchconeheading punchpin pressesthe recessejector pin pushes upscrew blank, readyfor thread rollingfingers carry the blank from station to station between blowsKey:metal being shaped (cold)dies, punches and cutter
Cold heading: from wire to screw blank in four stationsEach panel is one station of the same machine; circled numbers match the steps below.

How it works

  1. Cut a blank. Drawn wire (lesson 3.4) is fed off a coil, straightened and pushed through a feed tube. A cutter shears off a blank (a short slug) of exactly the right length.

  2. Upset with the first blow. Transfer fingers place the blank in a die (a hardened block with a hole). A punch strikes its end and upsets it (squashes it shorter and fatter) into a rough cone.

  3. Form the head. At the next station a heading punch flattens the cone into the final head. A pin on the punch presses in the recess, for example a cross or hex socket for the screwdriver.

  4. Eject. An ejector pin pushes the finished blank out of the die. A screw blank then goes to thread rolling (lesson 3.6), and often to heat treatment and plating.

Key facts

Materials
Low- and medium-carbon steels, alloy steels, stainless steel, aluminum, copper and brass
Typical parts
Screws, bolts, rivets, nails, pins, ball blanks, spark-plug bodies, small shafts
Part size
Typically from about 1 mm to about 30 mm in diameter, and up to a few hundred millimeters long
Precision
Typically about ±0.05–0.1 mm on diameters; heads slightly looser
Surface finish
Smooth, slightly shiny formed surfaces, no tool marks from cutting
Batch size it suits
Very large: tens of thousands to millions of identical parts
Tooling and machine cost
Die and punch sets: thousands of dollars. Multi-station headers: hundreds of thousands to millions
Speed
Small parts: often a few hundred per minute; large bolts: tens per minute

Strengths and limits

Strengths

  • Extremely fast and cheap per part
  • Almost no waste: no chips, nearly all the wire becomes product
  • Cold working makes the metal stronger, and the grain follows the head
  • Very repeatable parts from automatic machines

Limits

  • Tooling and setup only pay off in very large batches
  • Limited to fairly compact, round shapes made from wire
  • The metal must be ductile enough not to crack when squashed cold
  • Tight features (fine threads, precise bores) need extra steps

Where it's used

  • FastenersWood and machine screws, bolts, rivets, nails
  • AutomotiveWheel bolts, engine bolts, ball-joint studs, valve parts
  • ElectronicsTiny screws for phones and laptops, contact pins
  • ConstructionAnchor bolts, structural bolts, nails
  • BearingsSteel ball blanks before grinding

How to recognize it

  • A head that flows smoothly into the shank, with no seam or weld line.
  • A slightly rough or flattened tip on the far end, where the wire was sheared.
  • Letters or numbers raised or stamped on the head, pressed in by the punch (bolt grade and maker marks).
  • Identical parts by the thousand, typically sold in bulk boxes.

Compare with

Forging3.1cold heading is closed-die forging done cold, very fast, on small wire parts.Turning5.1a screw can also be cut from bar on a lathe, but that wastes metal and is far slower.Thread rolling3.6the next step for a screw blank: its thread is pressed in, also without cutting.

Watch it

Corey @ SmithReps · A one-minute overview of how screws are headed

Nedschroef Machinery · How a multi-station former shapes a part blow by blow

Arjaan Buijk · A simulation of the metal flowing at each station

INFASCO · A bolt factory, from wire coil to finished bolt

See real photos

Remember

  • Cold heading cuts wire into blanks and punches a head on them, cold, in a few blows.
  • Several stations in one machine shape each part step by step, hundreds of times a minute.
  • It makes almost every screw, bolt and rivet, with almost no waste.

More in Bulk forming

All 100 processes
3.1ShortForging (open-die and closed-die)Squeeze hot metal between flat or shaped diesOpen the lesson3.2RollingPull metal through the gap between turning rollsOpen the lesson3.3Extrusion (aluminum profiles and plastic pipes)Push metal or plastic through a shaped dieOpen the lesson3.4Wire drawingPull a rod through ever-smaller diesOpen the lesson3.6Thread rolling and tappingPress a thread onto a blank, or cut or press one in a holeOpen the lesson

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