Hydrostatic Extrusion – Advantages and Disadvantages
In hydrostatic extrusion the work piece is held in a sealed chamber surrounded by pressurized liquid. Hydrostatic extrusion is actually a form of direct extrusion. The force delivered through the ram is what pressurizes the liquid. The liquid applies pressure to all surfaces of the work billet. When the ram moves forward, it is the force from the incompressible fluid that pushes the work through the die, extruding the metal part.
A critical aspect of manufacturing by this process is setup. The metal work billet must first be tapered to fit through the die opening, thus creating a seal. This is done before adding the liquid, in order to prevent leaking. Since the liquid is under great pressure, this taper must be precise to create a robust bond. Many different shapes may be manufactured by this process, using a variety of materials. Liquid pressure from all directions also greatly decreases the chances of buckling of the work.
More article about Extrusion :
- What is Extrusion Process | Types Of Extrusion process
- Types Of Extrusion And Advantages of Extrusion
Hydrostatic extrusion may be performed at room or elevated temperatures, depending upon the manufacturing process. When performed hot, the liquid will insulate the work from thermal gradients between the container and work material.
An advanced variation of this process is called fluid to fluid extrusion. This process is basically the same, except that the part is extruded into a second chamber also containing pressurized liquid. The liquid in the second chamber is of a lower pressure than the first. Several different kinds of liquids are used when manufacturing by hydrostatic extrusion, including oils, waxes, melted polymers and molten glass.
Hydrostatic extrusion has not had much use in manufacturing industry, due to the complicated equipment and procedures, work preparation, long cycle times and dangers of working with hot, high pressure liquid.
Advantages of Hydrostatic Extrusion
- No friction amidst the container and billet. This minimizes the force requirements, allowing higher reduction ratios, faster speeds, & lower billet temperatures.
- Friction of the die can be largely reduced by a film of pressurized lubricant amidst the die surface and deforming metal.
- On applying high pressures, the ductility of material increases.
- Even flow of material.
- Large billets & large cross-sections are extruded.
- Uniform hydrostatic pressure inside the container eliminates the requirement of billets being straightened and extrusion of coiled wire.
- No billet residue is left on the walls of container.
Limitations of Hydrostatic Extrusion
There are a number of limitations in the hydrostatic extrusion, especially when a large volume of fluid is used in comparison with the billet volume, which is to be extruded. These limitations are as follows:
- Increased handling for the injection and removal of the fluid for every extrusion cycle.
- Decreased control of speed of the billet & stopping because of potential stick slip and enormous stored energy in the compressed fluid.
- Decreased process efficiency in terms of billet-to-container volume ratio.
- Enhanced complications, when extrusion is done at elevated temperatures.
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