Cold Heading Machine

Overview

A cold heading machine is an automated fastener manufacturing tool that progressively forms bolt heads, rivets, and screws from wire stock without heat. The machine uncoils steel or brass wire, shears it into blanks, and transfers each blank through a series of forming dies powered by a mechanical drive system. Cold heading produces fasteners with high strength and excellent surface finish, making it essential for producing bolts, rivets, and screws at volumes exceeding 1000 parts per day.

Cold heading relies on plastic deformation of the blank to fill die cavities under high pressure. Unlike machining, which removes material, cold heading compresses and reshapes the blank, preserving material and producing stronger parts with fine grain flow. The process is economical because wire stock has minimal scrap and cycle times are brief, 30 to 120 parts per minute depending on size.

The typical machine has five to seven forming stations arranged radially or linearly. The wire feed system straightens and positions stock. The cutoff unit shears blanks to length with ±0.05 mm repeatability. Transfer fingers then pass each blank from one forming station to the next. At each station, a hardened die pair forges the blank into the desired shape. Finally, the knockout system ejects the finished fastener.

How it works

The machine cycle begins when the feed nose positions a length of wire against the cutoff blade. As the main drive rotates, a mechanical linkage actuates the blade, shearing the wire to the target blank length. The blank drops into a transfer pocket.

The transfer cam, driven by the main shaft, rotates and opens the transfer fingers. The fingers grip the blank and lift it into the first forming station. Here, the upper die descends and strikes the blank against the lower die, plastic-deforming the end into a head shape. Forming pressure ranges from 800 to 2000 MPa depending on material and head diameter.

After the first heading, the transfer cam closes the fingers and rotates again, advancing the blank to the next station. Larger fasteners may require two or three heading strokes to fill the die cavity completely and achieve the final profile. Each station applies incremental forming, progressively building the final head shape.

Once all heading operations are complete, the blank enters the knockout zone. The knockout actuator drives the knockout pin upward, ejecting the finished fastener from the lower die. The part falls into a collection chute.

The main drive, typically a 15 to 30 kW electric motor coupled through a gearbox to a flywheel, maintains synchronized rotation of all cams and linkages. The flywheel stores rotational inertia, providing peak power for the forming stroke without motor overload. A speed controller adjusts the operating speed from 30 to 120 parts per minute, matching the cycle rate to die capacity.

Die life and material flow

The heading dies are the machine's most critical wear item. Hardened to 48–52 HRC, they can form 50,000 to 150,000 parts before the cavity edges begin to dull and produce dimensional creep. At that point, the dies are removed and hand-honed or sent for professional resharpening. Complete die sets, upper and lower cavities, cost 800 to 3000 EUR depending on head complexity.

Wire is fed at ambient temperature, so the process is called "cold" heading. The blank does experience localized strain heating during forming, reaching 50–80 °C in severe cases, but remains far below recrystallization temperature. This cold work hardens the fastener, increasing tensile strength compared to the annealed wire stock.

Material loss is minimal: the sheared wire is cut precisely to blank length, and forming is lossless. Only the cutting operation produces scrap, a small slug from the shear. For materials like stainless steel or brass, which are expensive, this efficiency is a major cost advantage over machining.

Setup and changeover

Changing from one fastener size to another requires swapping the heading dies, feed nose, and sometimes the cutoff blade. A trained operator can accomplish a complete changeover in 30 to 60 minutes. The drive system remains unchanged; only the die cavities and some wear surfaces are replaced.

Speed adjustment is done by changing gearbox ratios or via a variable-frequency drive on modern machines. Older machines use a mechanical speed control that adjusts the active cam angle, reducing the number of active forming strokes per motor revolution.

Applications

Cold heading is the dominant process for fasteners under M16 (5 mm diameter). Annual global production exceeds 400 billion cold-headed bolts and screws. Standard applications include:

• Hex head bolts and socket head cap screws
• Carriage bolts and eye bolts
• Rivets and semi-tubular rivets
• Slotted wood screws and sheet metal screws
• Fasteners for automotive, aircraft, construction, and electrical equipment

Specialty forms include self-drilling screws (with flutes for sheet metal), security screws with proprietary head designs, and captive fasteners with wires or springs pre-attached.

Economics

A production machine costs 80,000 to 250,000 EUR installed. Annual material cost (wire stock) is typically 2–5 EUR per 1000 fasteners. Labor is minimal, one operator can monitor 1–2 machines. The process reaches economic efficiency at volumes exceeding 50,000 parts per part number per year. For commodity fasteners, economies of scale push volumes to 10 million parts per year per machine.