An impact is a part formed in a confining die from a metal slug, usually cold, by rapid single stroke application of force through a punch, causing the metal to flow around the punch and/or through an opening in the punch or die. The four basis impacts are: reverse, forward, lateral and combination.

An impact implies a hammering action and can be differentiated from an aluminum extrusion whereby an ingot or billet is forced under applied pressure through a die opening to form an elongated shape or tube; and is, by a shade of meaning, different again from an impact extrusion, or back extrusion. The impact extrusion process combines extrusion and forging in a single press operation.

The first metal impact extrusion, a lead collapsible tube, is believed to have been produced in France around 1850. The first experimental work on aluminum impact extrusion was conducted in Switzerland in about 1914. In 1921, Aluminum Company of America produced the first aluminum impact extrusion in the United States.