Metal and Plastic Extrusion
The process of extrusion forces a solid material through a properly shaped cavity under compressive forces.
Extrusion is comparable to squeezing toothpaste through a tube, although some cold extrusion methods more practically resemble forging, which also warp metals by application of compressive forces. The process begins by heating the material; it is then loaded into the container in the press. A dummy block is positioned at the rear where the ram then presses on the material to drive it out of the die.
The extrusion is then stretched in order to give it better strength. If better properties are necessary then it should be processed using heat extrusion or cold extrusion.
The most widely used method for producing extruded shapes is the direct, Hot Extrusion process. Hot extrusion is done at high temperatures to keep the material from work hardening and to make it easier to ram the material all the way through the die. The largest drawback to this process is its price for machinery and constant maintenance.
Cold extrusion is done at close to room temperature. Advantages of cold extrusion are superior strength, good finish and dimensional accuracy, and cost-effectiveness due to fewer operations and the minimal machining required. Lead, tin, titanium, and steel are some of the materials that are normally used in cold extruding. Automotive pistons and gear blanks are made using this process.
Plastic extrusion is similar to the process of metal extrusion, the difference being the plastic pellets are extruded by being pressed through the die by a screw. This is similar to injection molding, but uses a die to form the profile versus using a mold for core and cavity.