Extrusion is a metal forming process in which a metal or workpiece is forced to flow through a die to reduce its cross-section or convert it into a desired shape. The process is similar to drawing, except that it uses compressive stress to extend the metal workpiece. The force used to extrude the workpiece is compressive in nature, which allows for large deformation compared to drawing in a single pass. The most common materials extruded are plastic and aluminum.

Here are some key points about the extrusion process:

• Working Principle: In this process, a piston or plunger is used to apply compressive force to the workpiece. The billet or ingot (metal workpiece of standard size) is produced first, and then the die, which is a small opening of the required cross-section, is used to force the work metal to flow through and convert into the desired shape. The extruded part is then removed from the press and heat-treated for better mechanical properties.

• Types of Extrusion: Extrusion processes can be classified into the following types based on the direction of flow of metal:

  • Direct Extrusion: The billet is placed in a heavy-walled container and pushed through the die by a ram or screw. There is a reusable dummy block between the ram and the billet to keep them separated.

  • Indirect Extrusion: The hot billet is loaded into a thick-walled container and forced through an extrusion die secured in a holder. The force for extruding is applied by a ramp along with an intermediate reusable dummy block. Metal flow from the die is in the same direction as the forward motion of the RAM since the surface of the billet length slides along the wall of the container. The extrusion force depends on the friction between the billet length and the container and the material.

• Advantages and Disadvantages: The advantages of the extrusion process include the ability to produce complex shapes with a high degree of accuracy, the ability to work with a wide range of materials, and the ability to produce parts with a high surface finish. The disadvantages include the high cost of equipment, the need for skilled operators, and the potential for defects in the extruded parts.

Extrusion is also used in the manufacturing of ceramics, plastics, and steel. The process allows for efficient, continuous production, and is used to create objects of a fixed cross-sectional profile by pushing material through a die of the desired cross-section.