Increased Density in Powder Metallurgy Products: How can this be Achieved?

November 20, 2019

Powder Metallurgy produced parts continue to find their way into countless machine types. In fact, if a new machine comes to market, there’s a good chance it’ll use a few sintered parts. Because the PM production process utilizes a density controllable metal forming technique, all sorts of applications become feasible when sintered components apply their capillary-loaded structures. However, what if the process needs to go in the opposite direction?

Process Densification Feasibility

In reading that last question, a client is clearly asking for less porosity. The customer desires the same level of geometrical precision, as performed on a dimensionally exact component, but the part structure should now be denser. Higher porosities ratios take parts densities in the opposite direction, and that’s a problem, one that presents an unacceptable outcome here. So is there a way to substantially increase the density of PM manufactured components? Absolutely, there are several techniques, and these methods all produce stronger, denser structural features.

Hybrid Powder Forging VS High-Pressure Forming

Production lines can use a best of both worlds approach to create denser sintered components. The powdered metal is compacted as usual, but then the sintering phase hits a higher note as it ramps up the temperature. Instead of the utilization of a particle “necking” thermal curve, the full force of the forging process densifies the mix. However, forging temperatures require cooling chambers, which may inadvertently change the physical and mechanical attributes of a cast workpiece. Alternatively, perhaps even more intuitively, the densification work can be done in the compaction chamber. In here, greater pressures are used to create a denser, heavier Green compact, which is then dispatched to the sintering stage. Variants of this densification technique exist. There’s a high-pressure, cold compression method, then there’s a warm compaction variation.

Sifting Through the Densification Alternatives

By varying the temperature or the compaction pressure, different structural toughness levels are indeed feasible. There’s also the additive variation method to consider. When waxes and lubricants are pulled from the mix, greater Green density ratios are realized. If finer powder phases are produced back at the PM atomization stage, again, denser compacted forms become that much easier to produce.

Absolutely, it’s easier to make porous components with powder metallurgy processing, but that doesn’t mean it’s that much harder to take the process in the opposite direction. At the discretion of the manufacturing manager, all kinds of hardening and densification methods are accessible. Only, variations in dimensional integrity may occur when these techniques are used, so further post-processing chores may be required after one of these Green strengthening techniques is applied.

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