Powder metal components should be designed based on several shape recommendations, aimed at making compacting feasible, as well as to minimize manufacturing costs.
As a summary, recommended shapes are a consequence of 5 important determining conditions:
1. Robust tooling.
The part shape must be designed so that the compacting tooling be robust, and does not break during operation. Basic considerations are as follows:
– Avoid cylindrical shapes perpendicular to the compacting direction.
– Avoid acute tooling transitions, and frontal shapes with thin end sections (knife tip).
– Avoid punches with thin wall thickness (< 1.5 mm), and deep and narrow notches.
– Avoid frontal holes of diameters lower than 1.5 mm, and blind holes too slender.
– Finish the frontal rims with flat end chamfers, and/or cylindrical zones of 0.5 mm in length.
The part geometry should be designed so that the part be ejectable from the compacting and/or sizing tool. Basic considerations are as follows:
– Avoid geometries that prevent the component ejection from the tool, like undercuts or lateral holes, non-progressive section changes in diameter, knurling, etc.
– Introduce de-moulding angles higher than 7º, which could be lower in some cases.
3. Minimum wall thickness.
The wall thickness of the tool filling cavity should be wide enough so that powder particles penetrate and fill the cavity efficiently.
In general terms, a minimum wall thickness of 1.5 mm is required, although up to 0.8 mm is possible in some cases.
4. Integrity of green parts.
A green part must have enough mechanical strength in order to handle it in process without affecting its integrity, and to prevent internal defects caused by ejection or handling. Basic considerations are as follows:
– Work with a minimum wall thickness of 1.5 mm, although up to 0.8 mm is possible in some cases.
– Flanges should have a thickness higher than 2 mm, which could be smaller in some cases. The thickness/width ratio of the flange can not exceed of 5.
– Put radii in all the tooling profile, and avoid sharp edges at the ends.
– Try to finish the frontal rims with flat end chamfers.
5. Gear shapes
Gears are under the same design criteria explained above, but some specific criteria must be added:
– Helical teeth must have an helix angle lower than 25º.
– The tooth tips and roots should have radii higher than 0.25.
– Minimum modulus must be 0.5, although 0.25 is achievable in some cases.