Process Characteristics

Unique aspects of CIP, as compared to die compaction, for P/M parts include:

• Hydrostatic application of pressure over all surfaces of the mold produces uniform powder density for simple and complicated shapes. Die-wall friction is not a factor in the densification process because of the elastic behavior of the mold.

• Organic binder or lubricant additions to the metal powders are not required to achieve useful green strength. In fact, these materials are detrimental because of the adverse influence on metal chemistry and related mechanical properties for many of the reactive metals commonly processed by CIP if all these materials were present.

• Shapes with high ratios (greater than 10) of length to characteristic diameter, can be densified and handled.

• Parts with reentrant and three-dimensional curved geometries can be made.

• Elastomer tooling can be combined with metal tooling inserts to exactly control certain part dimensions such as cylinder bores or outside diameters.

• Thin-walled sections and parts can be pressed.

• Parts so large that comparable uniaxial die pressing capacity does not exist in industry can be made because of the large area by pressure product available in the largest CIP vessels. For the 24 by 96 in. by 80 ksi vessel mentioned above, this maximum product is 818 MN (92,000 tons).

• Elastomer tooling costs are low.

Recognized limitations of the process include:

• Dimensional control is generally less precise than with metal die compaction because of the absence of exactly dimensioned reference surfaces and variability of the local poured powder density within the mold.

• Surface finish of cold isostatically pressed parts is rough compared to die-compacted parts except for areas in contact with hard tool inserts in hybrid molds.

• Production rates are low compared to metal die compaction.

• Elastomer molds have a relatively short life because of abrasive wear.

• Leakage of a mold in the CIP vessel due to mold tearing or poor closure and sealing practice results in loss of material due to contamination by the working fluid. With reactive fine powders, such as aluminum, in large molds water leakage into the mold can produce a hazardous exothermic reaction.

• Not all metals and alloys of interest are readily available in the suitable particle size distribution and shape for application in the process.

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