Lubricant Selection

In the majority of P/M applications, the lubricant is premixed directly with the metal powder. Stearic acid, zinc stearate, lithium stearate, and synthetic waxes, such as Acrawax, are the most popular lubricants. Lubricant selection is based primarily on the ability of the lubricant to adhere to metal particle surfaces. The amount of lubricant added depends on many factors, including composition of the metal powder, type of tooling, compacted density, and complexity of the part. Amounts generally vary from 0.5 to 1.5 wt%.

Lithium stearate is widely used in stainless steel powders because of its beneficial effect on compressibility. Lithium stearate and zinc stearate mixtures are used in brass and nickel silver powders to produce stainfree parts. Synthetic waxes with their low moisture and ash contents are widely used for high-density parts where ash residues are objectionable. Multicomponent lubricants permit the powder producer to adjust or influence the packing, pressing, and sintering characteristics of powder. The use of die wall rather than admixed powder lubrication is still in the development stage.

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