In the hydrostatic extrusion process the billet is completely surrounded by a pressurized liquid, except where the billet contacts the die. This process can be done hot, warm, or cold, however the temperature is limited by the stability of the fluid used. The pressure in the chamber transmits some of the fluid to the die surfaces, thus significantly reducing friction and forces. Because the hydrostatic pressure increases the ductility of the material, brittle materials can be extruded successfully through this method. Hydrostatic extrusion is generally carried out at the room temperature , typically using vegetable oils as the fluid, particularly castor oil because it is a good lubricant and its viscosity is not influenced significantly by the pressure. The process must be carried out in a sealed cylinder to contain the hydrostatic medium. The fluid can be pressurized two ways:
1. Constant-rate extrusion: A ram or plunger is used to pressurize the fluid inside the container.
2. Constant-pressure extrusion: A pump is used, possibly with a pressure intensifier, to pressurize the fluid, which is then pumped to the container.
In the following video we can see that in the left side of the screen there are various components involved in the hydrostatic extrusion process which includes the pressing stem meant for forcing the upper die block against the work-piece, the initial work-piece before deformation, the cylinder containing the working fluid with the seals all along its boundary to prevent the leakage of the fluid, the lower die block to shape up the cross section of the final extruded component, the die back up to prevent movement of the lower die. The right side of the screen shows the working of this technique. As the pressing stem is moved in downward direction the liquid in the chamber gets compressed and pressurised hence it enables the work-piece to get compressed all along its exposed surface and forces it to pass through the lower die orifice with continuous and uniform force.