Although Powder Metallurgy technology offers considerable design freedoms, there are a number of “dos” and “don’ts” to be borne in mind when designing a product with the process in mind.
These are highlighted in the following guidelines:-
The aspect ratio (i.e. length to width ratio) – the density variations created by friction effects between the powder feedstock and the tooling mean that, even with double-ended compaction, aspect ratio should be limited to no more than 3:1.
Re-entrant features such as grooves, reverse tapers or lateral holes, cannot be directly formed by Powder Metallurgy as they would prevent the part from being ejected from the die. If needed, such features would have to be introduced by machining of the sintered part.
Bevels would require feather-edged punches, which should be avoided. If possible, a bevelled edge should end in a small flat, thus avoiding the feather edge.
Chamfers are preferred to radii on component edges, again to avoid the need for feather-edged punches
Abrupt changes in section
Abrupt changes in section should be avoided as they introduce stress raisers that can lead to cracking due to springback in ejection.
Radii rather than sharp corners in the plan view section should be incorporated, again to avoid stress raisers.