Parts made using powder metallurgy processes are gaining ever increasing importance, particularly in the automobile industry. 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 for the press die and internal lubrication of the powder mixture, enabling maximum compression.
In the sintering process, in which the green compacts are heated to slightly below melting point, the material is then compressed further. In addition, fine graphite goes into a solution with the metal, increasing the mechanical strength of the workpiece.
Special powder mixtures exist for self-lubricating sintered parts. These special mixtures contain coarser graphite that requires a smaller amount for the solution during the sintering process. The graphite particles are mostly incorporated into the matrix of the workpiece in an intact condition and are exposed step by step during the lifespan of the part, which allows graphite to develop its lubricating effect.
Only consistent raw material quality and reproducible process parameters guarantee the dimensional accuracy and perfect quality of precision parts made in powder-metallurgy processes.