Impact extrusion is a cold metal forming process typically used to make collapsible tubes out of soft metals through a tool and die process. Unlike traditional metalworking processes, impact extrusion does not use heat to alter the shape of metal. Instead, it uses high pressure and force to change the shape of a metal material.
Common materials processed using impact extrusion include aluminum, brass, tin, steel, stainless steel and magnesium. The softer metals are most commonly used as there is great physical deformation which occurs in the process. Various industries such as automotive, electrical, pyrotechnics and packaging use the tubing produced by impact extrusion. During the process, a piece of metal, or a slug is placed into a die mold and forced by a punch and hydraulic press into the mold.
It deforms under the pressure to fit the punch on one side, and the mold on the other. The force used must exceed the elastic limit of the material in order to mold it. Reverse, forward or combination impacting are the three common types of impact extrusion which are chosen depending on the intended use of the extruded part and its required characteristics. Products such as airbag canisters, ammunition casing, gas cartridges, filter housings, nozzles, toothpaste tubes and extruded bottles are all produced using the impact extrusion method.
Advantages to using impact extrusion include savings in terms of both time and money. The process is fast, especially when the tool and die machines are combined with automatic feeding equipment. Piece to piece consistency among extruded parts is high, thus eliminating much of the need for secondary machining processes or finishing.
The cold forming, or cold working, process is also a minimal waste process as the material is not cut away or melted away; rather it is all forced into the new shape minimizing lost material, and allowing for expensive metals to be used effectively without fear of wastage. The properties of the material worked on are altered under the great pressure of the process. The hardness and yield strength are increased greatly, making cold extruded parts such as cold headed fasteners able to be used for heavy duty and high pressure applications.
The resulting impacted part is dense and porous-free. The cross-sectional area of a piece is decreased however, and there may also be residual cracks in the surface due to the pressure it is placed under. The process can also be used to produce long extrusions for decorative and aesthetic purposes.