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 tool sets, 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).
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