A novel extrusion process with its unique machinery is the topic of this relatively complex case study. It begins with a general need for a method to improve material properties by deformation processing. The end result is quite a detailed design of a machine to carry out Equal-Channel-Angular-Extrusion metalworking. Metal bars are forced in this process through a bent channel and thus undergo strain hardening while preserving their size and shape. The benefits of this process are also explained.

The Initial Need

Plastic deformation in metal forming is used for two purposes: to change size and shape, and to improve material properties such as ductility, strength, and toughness. Forging, rolling, and extrusion are examples of forming and shaping processes in which adding strain to a workpiece results in refining the grain size, making the microstructure more uniform, and work hardening of the metal. Work hardening and finer grains are responsible for an increase in the shear strength, and hence the overall strength, of the material. This increase results from entanglements and impediments of dislocations by shear deformation, which usually takes place at 45δ to the direction of the applied load. The greater the strain induced in the material during processing, the more the entanglements, and hence a higher strength is obtained. Metalworking can also remove metallurgical casting defects, such as cavities and voids, and produce desired textures.

Adding strain is used extensively in metalworking processes— for example, strengthening wire by reducing its cross-section by drawing it through a die, forging the head of bolts, and producing sheet metal for automobile bodies and aircraft fuselages by rolling.