The following series of guides are intended to act as an aid to engineers and designers wishing to produce cost effective designs for advanced ceramic manufacture. The design tips also refer primarily to components which have to be finish ground to tight tolerances.
1. Design for compressive stresses. Where possible avoid tensile and bending stresses. Almost all advanced ceramics have very high compressive stress capabilities, but only a few have high tensile stress capabilities.
2. Where possible, reduce the section thickness of the component (only use the ceramic where it is doing ceramic work). Try to relieve sharp corners by radii or chamfers. The generation of perfectly sharp corners is difficult due to the almost inevitable radius on the corner of the grinding wheel used to shape the feature (approximately 0.01mm radius). However, if a sharp corner is required, consider using an undercut.
3. Where possible, dimension a component to >+/-1%. This then often allows the manufacturer to produce the component ‘as-sintered’, thereby reducing the amount of diamond grinding required and more importantly – the cost.
4. Locate holes away from edges. Also, always try to keep the spacing between holes as large as possible (preferably > 2mm)
5. If bolt holes are required, it is better to make the holes size larger or use slots rather than having a tight tolerance on the hole spacing.
6. If a blind hole is required, keep it as shallow as possible.
7. Screw threads of greater than M3 can be ground (both internal and external). However, it is recommended that helisert screws are used to increase the strength of the assembly. Also, it is worth considering the use of a metal insert.
8. Try to limit the projected area. Large projected areas may require large and expensive toolsets, which also require large presses.
9. Try to keep the location techniques simple. Mechanical fastening, shrink fits, press fits and high strength adhesives are all possible depending on the materials to be joined.
10. Try to specify surface finishes in terms of lapped ( < 0.1 μm Ra), ground (< 0.6 μm Ra) or preferably as sintered (nominal 1-2 μm Ra).
In general,the less we do to the ceramic part after it is sintered,the less it cost.Here is a list of the processing after sintering in order of cost increasing to ceramic part.
sintering grinding lapping polishing
The difference choice of machining also cause the different cost of ceramic part.Below there is a list of machining operations in order of increasing to ceramic part.
surface grinding cylindrical grinding milling or drilling lapping hand finishing
Avoid sharp internal corner and undercut to save the cost and away from stress riser.Avoid knife edge features,because the brittleness of the ceramics.Provide radius and chamfer on each edge to prevent from chipping whenever possible.Tight tolerance causes expensive cost.