Especially in the automobile industry, parts made in powdermetallurgy processes are of ever increasing importance. For the production of sintered parts, metal powders are mixed with small quantities of additives such as waxes and graphite. Under high pressure, these powder mixtures are then pressed into so-called green compacts. In this process, graphite both ensures reduced wear of the press die and internal lubrication of the powder mixture, because it allows maximum compression. In the sintering process, where the green compacts are heated to slightly below the melting point, the material is then further compressed. Furthermore, fine graphite goes into solution in the metal and increases the mechanical strength of the workpiece.
There are special powder mixtures for self-lubricating sintered parts. These special mixtures contain coarser graphite that only goes into solution to a small extent during the sintering process. The graphite particles are incorporated into the matrix of the workpiece mostly in intact condition, and are exposed step by step during the life of the part, which allows graphite to develop its lubricating effect.
Only a constant raw material quality and reproducible process parameters guarantee the dimensional accuracy and perfect quality of precision parts made in powder-metallurgy processes.