How Hydraulic Thread Rolling Works — Step by Step

Rolling is a forming process in which a blank is pressed by a tool with the required profile so that the metal plastically flows into that profile. Hydraulic thread rolling is therefore a chipless process: the machine exploits the cold ductility of the material, and the blank takes the thread form under die pressure.

Cold thread rolling dates back to 1831, when screw machines were already producing fasteners for railway sleepers. Widespread use for precision threads only came after 1940 — earlier blank materials were simply not suited to rolling. Better material properties, improved dies and more capable rolling machines brought the process to carbon steels, alloy steels (including stainless and tool steels), bronze, brass, aluminium, copper, nickel, powder-metallurgy parts and plastics, for parts ranging from taps and engine bolts to spindle and lead-screw threads and thin-walled hollow components.

During rolling the thread is created by redistribution of the blank material displaced by the die profile — no chips are removed, so material utilisation is close to 100% and the grain flow follows the thread instead of being cut through.