Design for Powder Metallurgy

Several design rules must be considered to make parts efficiently and economically by the powder metallurgy process:

1. The design must be such that the part can be ejected from the mould or die. Parts with straight wall are preferred. No draft should be required for the ejection of a part from a lubricated die [as shown in Figure 3.6.6(a)].
2. In designing the part, consideration should be given to the need for the powder particles to flow properly into all parts of the mould or die. Therefore, thin walls, narrow splines, or sharp corner should be avoided (should be thicker than 0.762 mm).
3. The shape of the part should permit the construction of strong tooling. Dies and punches should have no sharp edges. Reasonable clearance must be provided between the top and the bottom dies during pressing.
4. Since pressure is not transmitted uniformly through a deep bed of powder, the length of the part should not exceed about two and half times of the diameter.
5. Very close tolerance in the direction of compression should be avoided.
6. Shape of the parts should be kept as simple as possible and should contain with few levels and axial variation. Holes should not be designed in the direction of pressing [as illustrated in Figure 3.6.6(b)]
7. Provide sufficiently wide dimensional tolerance whenever possible. Wide tolerance means that the part can be made more economically with a longer tool life.
8. In designing flat section of high density, enough section thickness should be provided otherwise the punch may break under pressure.
9. Parts made through powder metallurgy may be bonded by assembling in the green condition and then sintering together to form a bond assembly.
10. As far as possible, abrupt changes in the section thickness should be avoided. [as illustrate in Figure 3.6.6(c)]