Breviary Technical Ceramics






7.2.2 Influence of the Forming Process

Similarly to the manufacture of metallic or polymeric materials, the manufacturing process for ceramic parts possesses not only certain advantages but also has its limitations.

Thus for example, using slip casting, parts with constant wall thickness can be manufactured, but only up to a maximum of a few millimetres (depending on the material). It is more difficult to manufacture parallel surfaces, since the removal of the cast part from the mould is more difficult. Undercuts are also difficult and only possible through the use of complex, multi-part casting moulds.

Tubular or bar-shaped parts are usually manufactured by extrusion. Here, the manufacturing skill lies in retaining the cross section of the body and in avoiding deformation (sagging, ovalising) both axially and radially.

Injection moulding permits the production of very complex forms very close to their final dimensions. The tooling costs and batch sizes represent a considerable factor in the cost calculations.

The isostatic pressing technique is used mainly for the production of blanks with a particularly uniform density. These are subsequently processed further using chip-forming operations such as turning, milling, boring, grinding or cutting (using diamond tools).

Dry pressing is a process often used for the Mass Prod.s production of smaller parts. This process allows the economical production of relatively flat parts with a height to wall thickness ratio < 4 (in special cases < 8) and with no excessive height differences (blind holes, steps, etc.). The pressing tools are subject to high wear due to the high hardness of the ceramic powders. The lifetime of the tools is therefore limited if sufficiently accurate dimensions are to be maintained in the parts.


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