Cold Isostatic Pressing Tooling

Isostatic pressing uses flexible tooling of neoprene rubber, urethane, polyvinyl chloride, or other elastomers. Natural rubber is widely used, particularly when thin-wall tooling is required. It is also used for pressing complex shapes when more rigid tooling would present problems in extracting the pressed part from the mold and in applications requiring disposable tooling. Where more rigid tooling is required, polyvinyl chloride and urethane should be specified.

A. Thin-wall tooling: The flexible mold is made using a form that is dipped into rubber, plastisol, or neoprene. This type of mold is very flexible and is suited for highly compressible material; however, it must be supported for handling and proper shape control. This type of tooling is very inexpensive. Standard and custom shapes can be purchased commercially.

B. Rigid tooling: The rigid tooling is usually made by casting urethane into a two part form. The principal advantages of this type of tooling are good shape definition, mold durability, chemical resistance to commonly used pressing fluids, and the mold usually does not require a support canister. The drawbacks of the rigid mold type are the cost, inability to press highly compressible materials, geometry limitations since the part must be removed from the relaxed mold, and adhesions of certain powders to the mold wall causing breakage of the part upon decompression.

Regardless of the mold type selected, compact breakage sometimes occurs. This can be caused by one or several of the following, and possible solutions to the problem are given in each case:

• • Entrapped air in compact - Vibration during filling or removal of air from the mold by vacuum may be necessary prior to pressing.
• • Rapid depressurization - Decompression must be slowed.
• • Adhesion of a mold to the compact.
• • Poor green strength - Binders may be necessary in some cases.