Isostatic Pressing

Isostatic pressing is generally used to produce large PM parts to near-net shapes of varied complexity. Unlike conventional PM, in which the powder is compacted through direct contact with tooling, isostatic pressing confines the metal powder within a flexible membrane or hermetic container which acts as a pressure barrier between the powder and the pressurizing medium, liquid or gas, that surrounds it. The use of this pressurizing system ensures a uniform compaction pressure throughout the powder mass and a homogeneous density distribution in the final product.

For Cold (or room temperature) Isostatic Pressing (CIP), the container is typically a rubber or elastomeric material; the pressurizing medium is a liquid such as water or oil. Free of die frictional forces, the powder compact reaches a higher and more uniform density than would be obtained using conventional cold die compaction at the same pressure. In CIP processing, the part must be sintered (solid-state diffused) after removal from the mold.

For Hot Isostatic Pressing (HIP), the hermetic container for the powder is made of metal or glass and the pressurizing medium is a gas (inert argon or helium). At the elevated temperatures the process employs, the hermetic container deforms plastically to compact the powder within it. The combination of heat and pressure during the process eliminates the need for a supplemental sintering step. Removal of the HIP "can" (container) after processing is an additional requirement not found in other PM processes.

The advantages of the isostatic pressing process lie in its capability to produce parts of much larger sizes than is possible with other PM processes, with a virtually unlimited capability for complex shapes and geometric features. What’s more, it is applicable to difficult-to-compact and expensive materials such as superalloys, titanium, tool steels, stainless steel, and beryllium, with material utilization that is highly efficient. And, using the HIP process, parts can be produced that offer fully dense materials with isotropic mechanical properties equal or superior to those of cast and wrought materials.

However, isostatic pressing is applicable in general only to small production quantities, typically less than 10,000 pieces annually. It is a more costly method than other PM processes due to its slow processing speed and the need for expendable tooling. Lastly, it is a near-net shape process technology suited to parts with much wider tolerance requirements than other PM processes can produce.

Typical Isostatically Pressed Products—cutting tools, automotive cylinder liners (CIP), aircraft and marine gas turbine components, corrosion resistant components for petrochemical equipment and nuclear reactors, medical implants

Typical Markets Using Isostatically Pressed Parts—aircraft, aerospace, military, medical, chemical processing