Dimensional and Geometrical Precision of Powder Metallurgy Products

September 26, 2019

Whilst cast parts can exhibit dimensional inconsistencies, powder metallurgy products are designed to repress such manufacturing glitches. A casting might expand because it’s still soaked in smelting heat, but PM produced components don’t require anywhere close to that amount of metal-transformative energy. Because of that hallmark feature, powdered metals retain their Green compacted form. Even after the component has passed through the heated sintering phase, it stubbornly maintains dimensional and geometrical integrity.

Anomalous Shape Changes Are not an Issue

Remember, it’s the compaction die that imparts a detailed shape to the powdered metal and its additives. Not wholly solid, the grains push up against one another and create microscopic voids. This Green compact then heads out to the sintering chamber, where it’s thermally treated. Importantly, the powder does not melt, it fuses and consolidates. At process end, the powdered metal coalesces. As for the voids, they’ve formed into a network of lubricant-filled capillaries. Sharp part’s corners or intricate surface indentations, in fact, all geometrically dense part’s features remain fundamentally unaltered after the sintering stage has concluded. Aside from the ability to incorporate a self-lubricating feature, dimensional stability is perhaps the most beneficial trait gained when using sintering technology.

Net Shape Manufacturing Accuracy

Admittedly, especially when high-tolerance engineering thresholds are crucial, any possible dimensional change must be noted. Let’s say a manufacturing project has just secured a contract for a new run of aerospace-grade components. Sure, as covered above, powder metallurgy products exhibit few if any dimensional changes after they exit the sintering chamber. However, some engineering applications demand the highest measurable size tolerances when submitting a part’s drawing. So, with that in mind, are there any possible instances during the sintering work where a component’s geometrical profile could fall short of such next-level design instructions? Well, tiny changes in the granulometric fractions, the size and uniformity of the atomized metal powder could cause a slight change in a PM produced part’s geometrical characteristics. Also, pore over-reduction occurrences could cause a finite amount of component shrinkage.

Just to repeat the point, powder metallurgy processing is a very precise manufacturing method, one that can output numerous dimensionally and geometrically accurate components without any issue whatsoever. However, at least when working with the absolute highest of engineering tolerances, finite-size errors are possible. A rigorously controlled sintering mechanism will eliminate 99% of such errors. By fine-tuning the process, the necking or metal coalescence behaviour is better regulated, which in turn brings more control to the capillary formation process. For that last 1% of size and shape variance, post-process machining will immediately eliminate any dimensional inconsistencies.

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