Manufacturing Processes - Hot & Cold Isostatic Pressing
Isostatic Pressing Processes
Isostatic pressing is a powder processing process that falls in the category of forming under the general category of manufacturing processes.
There are 2 types of isostatic pressing processes:
- Hot isostatic pressing (HIP), where components are loaded into a furnace and then placed in a pressure vessel so that heat and pressure can be applied simultaneously .
- Cold isostatic pressing (CIP), where powder is sealed in a flexible mould and is then subjected to a uniform hydrostatic pressure without heating.
Hot isostatic pressing (HIP) is used, as indicated, to press and sinter simultaneously in an inert atmosphere (usually using Argon gas). The powder in the hot isostatic pressing process has to be protected from the atmosphere so that oxide films can be avoided. Hot pressing needs the powder to be heated, pressurised and cooled in the protective atmosphere.
Cold isostatic pressing is used to produce green compacts which typically will require further processing stages.
Both processes are expensive from an operating cost perspective but HIP should be considered a very expensive option, the need for a protective environment and the slow cycle time of the process leads to inevitable cost implications. On the positive side there is 100% materials utilisation and the process is reasonably flexible.
The finished products can be produced in solid 3D shapes, mostly utilising metal or ceramic composites, and have relatively low or no porosity. There can be some distortion when producing high aspect ratio components.
One method of producing a finished component using HIP is to fill a formed container with powder, after which the container is evacuated of all gas and is sealed. The container is then placed inside a furnace inside the pressure chamber and the isostatic pressure (utilising an inert gas) and heat is applied.The component using this method takes the shape of the container.
An alternative method is to subject pre-formed components to temperature and pressure as a finishing process that sinters the powder to higher density components.
Note: Isostatic pressure is pressure that is applied from all directions simultaneously.
The process because of the operational costs is normally reserved for the production of high value components that can bear the associated production costs.
Hot Isostatic Pressure Process
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