Cold Isostatic Compaction (CIP)

• CIP is a compaction process in which isostatic fluid pressure is applied to a powder mass at room temperature to compact it into desired shape. The powder parts can be compacted up to 80-95 % of their theoretical densities. Water or oil can be used as pressuring medium. • Process details: High density near-net shape green parts, long thin walled cylinders, parts with undercuts can be readily fabricated. In this process, pressure is applied simultaneously and equally in all directions using a fluid to an elastomeric fluid with powder at room temperature. Sintered CIP component can reach up to 97 % of theoretical density. Steps in this process is shown in flowchart.

Good mould filling is required in CIP because the initial powder distribution and density affect the preform shape. Powder size, shape, density and mechanical properties affect the flowability of powder into the mould and the packing density. Optimum pressing is obtained by using a free-flowing powder along with controlled vibration or mould tapping. Materials used for flexible moulds are natural, synthetic rubber like neoprene, urethane, nitrile, silicones. During pressing, high density is achieved at a low pressure, while the green strength of the compact rises linearly with pressure. The pressure applied can range from 100- 400 MPa. Initially the applied stress (exactly shear stress) serves to improve the density of the compact by particle sliding and rotation. In the next stage, deformation of powder particles occur and particle characteristics like shape play vital role in deciding this stage. • Irregular particles which interlock with one another and also deform during both the stages, tend to densify much easily than spherical powders. In the case of spherical powders, in spite of their higher initial packing densities, particles do not mechanically interlock with one another and hence do not easily deform. Hence high pressures are required for their compaction.

Types of cold isostatic pressing:
Wet bag process: IN this, the mould is directly in contact with the fluid. This reduces the productivity, since the bag has to be removed every time before refilling. Tooling costs are reduced in this.
Fixed mould process: the mould is fixed in the pressure vessel and powders are filled in situ. The tooling has internal channel into which fluid is pumped. This is an automated process in which the powder filling, compaction, depressurization and removal of green parts are done continuously. This involves higher tooling cost, but has higher production rate.

Advantages of CIP:

Uniform, controlled, reproducible densification of powder; long, slender parts can be pressed; neat net shape forming; short production times; economy of operation for complex and large parts.

Applications:

Metallic filters made from bronze, brass, stainless steel, Inconel, Monel, Titanium, high speed tools, carbide tools. Also ceramic parts such as sparks plugs and insulators are made by this method.