The various techniques used to machine ceramics
Ceramics may be machined for different reasons:
- to produce a part from a material blank (billet/disc/plate etc.)
- to machine a part, formed by a prior pressing or moulding process, down to its final tolerances (using a “grinding” stage)
Machining of green (unfired) or fired ceramic parts
Machining can be performed on green or sintered blocks. These are two very different processes.
Post-sintering machining of technical ceramics
The machining is performed after the sintering cycle (firing).
This process is used to produce prototypes or production runs of parts with a ratio of size to dimensional tolerance which could not be achieved by pressing or moulding.
Since sintered ceramics are very hard but also highly abrasive, conventional equipment must be modified before it can be used. All equipment must be adapted appropriately, e.g. by using diamond tools (grinding wheels/drill bits/lapping tools, etc.) and by using water as the lubricant.
Clearly, the machining cycle times and the rates of tool consumption when working on this material are not at all comparable with the conventional machining of metals.
Despite the expense, this process nonetheless offers valuable benefits when there is a requirement to obtain very precise tolerances.
Green machining of technical ceramics
Before it is fired, the material is described as “green”. The aim is the same as for machining sintered material.
The main difficulty is in making provision for subsequent shrinkage, since the density of the ceramic material will increase further, resulting in a certain percentage of shrinkage after firing. It is thus more difficult to achieve very tight tolerances.
Against this, green machining is much less expensive in terms of tooling and in particular the machining cycle times are much shorter compared with machining sintered material.
|Type of part
|Size of production runs
|Machining of blocks after sintering
|Simple to complex
|Green machining of blocks
|Simple to complex
It is also possible to machine “pre-sintered” blocks (which are debinded and semi-sintered in order to start the process of hardening the material) and thus to combine the advantages offered by these two methods.
A collaborative project based on the machining of ceramic parts from feedstock in bar form
As a natural consequence of the closer ties between Bouverat-Pernat and Nanoceram the concept of applying bar machining technology to ceramics was proposed. The high levels of productivity offered by this process should dramatically reduce the costs associated with machining ceramics.
This idea grew into the FUI Punchi project: an innovative ceramic bar machining process.