Cold extrusion, also defined as the compressive forming process, refers to the process in which metal is passed through high pressure to achieve high strength and stability. It is normally conducted at room temperature or slightly warmer temperatures. Some metals that can be extruded through this process include copper, steel, tin and aluminum alloys.
This process involves a billet being forced through a die at room temperature, which produces continuous cross-section products. There are three main variations of the extrusion process;
Forward Extrusion
It is also referred to as direct extrusion. This process occurs when the direction of material flow in metals is similar to the movement of the pressure being applied. In this process, the billet is placed in a heavily walled container then a ram or screw is used to push the billet through the die. Many manufacturers use this process as the cross-sections are uniform over the entire length of the metal. This process facilitated the production of parts of more intricate shapes.
The main disadvantage of forward extrusion is that more force is required to move the billet through the container’s entire length.
Backward Extrusion
It is also referred to as indirect extrusion. In this process, the die is constant, whereas the billet and the container move together. During the process, the direction of the material flow in the metal is opposite to the movement of the force being applied. Backward extrusion is used in the production of hollow shapes. This is achieved by forcing the ram into the billet, which forms a tubular part with material around it.
This process facilitates low friction forces as the friction involved is only between the die and the container and is determined by the length of the billet. This is because the comparative lesser force is required for extruding the material than in forward extrusion.
Lateral Extrusion
In this extrusion process, the die opening is located on the side of the container. When force is applied to the billet, the extrudate is pushed through the side opening of the container. In this process, the material flow of the metal is perpendicular to the movement of the force being applied. Literal extrusion facilitates the production of lengthy parts in a single operation.
The main advantages of cold extrusion are that there is no oxidation, the surface finishings are much smoother, and the products have a high tolerance. Also, the extrusion speed is much lower at such temperatures.
In conclusion, cold extrusion has evolved massively over the years due to technological advancements. It is essential in the manufacturing industry as it facilitates the production of both hollow and solid products.