upsetter

An upsetter is a horizontal forging machine that compresses metal between two dies to increase its cross-sectional area while reducing its length. Unlike vertical presses, the upsetter applies force along the axis of the workpiece, pushing it back into itself. This action is called upsetting, and it generates the localized thickening that gives the machine its name. Common applications include forming bolt heads, rivet tips, connecting rod eyes, and flange bosses on shafts.

The machine consists of a stationary die mounted on one end and a moving ram (or header) on the other. The workpiece is gripped or positioned between them, and the ram accelerates toward the die at high speed, delivering a sharp impact rather than slow squeeze. This impact method allows upset forging to work material faster and with less total pressure than a static press would require, though it demands more rigid equipment and better die design to handle the shock loads.

Upset forging machines range from small header machines that form fasteners under 1 inch diameter, to heavy industrial upsetters capable of working bars 3 inches or larger. Semi-automatic machines feed bar stock continuously, shearing and positioning each blank automatically before each stroke. Fully manual machines require operator intervention for each piece. The speed, force, and die geometry must match the material; aluminum and brass upset easily, while high-carbon steel and stainless steel demand hotter blanks and more powerful machines.

Die wear is the primary maintenance concern. The concentrated impact of upsetting can crack or deform dies faster than in other forging processes, especially if the metal is too cold or the geometry creates a stress concentration. Setup time matters too: changing over from one part number to another requires swapping dies, adjusting stops, and testing the blank positioning, which can take hours on larger machines.

The upsetter sits alongside other impact forging equipment such as drop hammers and screw presses in the hot-forming shop, but its horizontal action and high speed make it the workhorse for high-volume headed-fastener and tubular-fitting production. It is sometimes called a horizontal press or, in older texts, a header machine, particularly in the fastener trades.