Lubrication

Lubrication is essential to reduce friction between the pressed compact and the rigid tool components when compacting metal powders in steel or carbide tooling. Extremely high part ejection pressures and, ultimately, seizing and excessive tool wear result without proper lubrication. In addition, the surface quality of the part is detrimentally affected. Although much work has been done with systems where the tooling itself is lubricated, these systems generally have not proved effective high-volume P/M parts production. Parts produced by isostatic compaction do no require lubrication, due to the absence of high frictional forces during this type of processing.

Compacting grade metal powders are lubricated to facilitate part ejection from the die and to minimize die wear. Lubricants can strongly affect compacting and sintering properties of a powder. For this reason, powder producers try to optimize amount, composition, and structure of a lubricant to not only reduce friction during powder compaction, but also to protect the powder against oxidation and to obtain consistent apparent density and powder flowability, proper dimensional change during sintering, and maximum and consistent mechanical properties of the sintered parts.

Although a lubricant largely evaporates and/or decomposes in the preheating zone of a sintering furnace, its interactions and reactions with the metal powder can have critical consequences. Potential problems range from lubricant segregation, burnout, and blistering to carbonization and lubricant residue interference. Lubricant performance also depends on part density, metal powder composition, and particle size.

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