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Green machining

At Cerafast the green phase means creating a block by pressing atomised grains.
This block can then be machined and the ceramic shaped by machining.

The process
The initial stage of this process produces a block of compressed powder whose mechanical resistance depends on the organic binders contained in the pressing grain.

The right choice of pressing grain gives an ideal performance when green machining the product (mechanical resistance, cutting suitability).
Cerafast uses green machining on 3- and 5-axis HSC centres so as to benefit from fast prototyping and best cutting conditions.
The machining techniques are similar to those used for metals. Green machining of ceramic requires cutting parameters (feed speed and cutting speed) close to those used for steel, these parameters having nothing in common with those used in grinding.
An alternative to green machining is to work on a pre-sintered product (biscuit) when properties are insufficient after pressing.

Essential criteria
Accurate and capable of duplication to more or less 2m, our machining centres can be used for small and middle-scale production.
However, in order to preserve such accuracy the material’s fritting conditions must be carefully controlled. The machined item will shrink by about 20% during thermal treatment. This shrinking in the ceramic is accompanied by distortion which varies depending on dimensions. To take into account the influence of sintering, machining must be done with 5 to 10 times greater accuracy than that specified (machining tolerance = 0.01 mm for 0.05 signed for).

Cerafast has selected machine-tools which are precise enough to ensure the product’s geometric accuracy, as well as the means to control coherence with specifications.

Standard dimension accuracy at kiln exit is less than approximately 1% out on serial production.
In order to complete the service, Cerafast’s perfectly adapted grinding tools ensure the final conformity of the items to the client’s requirements.

The green machining of ceramic thus allows fast, customised shaping when used in conjunction with the techniques of fast prototyping. It becomes easy to move from concept to realisation, at short notice and minimised cost.
This technique has other advantages:

  • Green machining does not damage the material, and does not induce defects that cannot be corrected during thermal treatment
  • Applicable to all ceramic materials, this process does not require a specific development of the material for its shaping.