Powder metallurgy is the process where by metal parts in large quantities can be made by compressing and sintering various powdered metals such as brass, bronze, stainless steel, and iron. Compressing of the metal powder into the part to be made is done using accurately formed dies and punches in special types of hydraulic or mechanical presses. The "green" compressed pieces are then sintered in an atmosphere controlled furnace at high temperatures, causing the metal powder particles to be bonded together metallurgically. A subsequent sizing or coining operation and supplementary heat treatments may be employed. The physical properties of the final product are comparable to those of cast or wrought products of the same composition, if the parts are processed to provide high density. A lower density will result in lower physical properties.
Advantages of Powder Metallurgy Parts requiring irregular curves, eccentrics, radial projections, or recesses often can be produced only by powder metallurgy. Parts that require irregular holes, key-ways, flat sides, splines or square holes that are not easily machined, can usually be made by this process. Tapers and counter bores are easily produced. Axial projections can be formed but the permissible size depends on if the powder will flow into the die recesses. Slots, grooves, blind holes, and recesses of varied depths are also obtainable.
The process provides close dimensional tolerances, minimal machining, good surface finish, and excellent part to part reproducibility for moderate to high volume part production.
Limiting Factors in the Powder Metal Process Features should be avoided that result in tooling with thin sections or sharp inside corners. Multiple axial projections result in complex tooling and there are limitations on the number which can be formed. Undercuts, cross holes and re-entrant angles cannot be molded and therefore must be machined after sintering. Tolerances in diameter usually cannot be held closer than .001 inch and tolerances in length are limited to .005 inch.
Of all the mass productionmethods utilized by industry today, the powdered metal process is one of the most economical for fabricating high quality, high strength metal parts to precision tolerances.