Powder Metallurgy is a highly evolved method of manufacturing reliable net shaped components by blending elemental or pre-alloyed powders together, compacting this blend in a die, and sintering or heating the pressed part in a controlled atmosphere furnace to bond the particles metallurgically. The P/M process is a unique part fabrication method that is highly cost effective in producing simple or complex parts at, or close to, final dimensions. P/M processing provides the following advantages:
-Production of complex shapes to very close dimensional tolerances, with minimum scrap loss and fewer secondary machining operations.
-Physical and mechanical properties of components can be tailored through close control of starting materials and process parameters.
-Particular properties can be improved through secondary processing operations such as heat treating and cold/hot forming.
After the metallic powders have been produced, the conventional PM sequence consists of three steps:
- Blending and mixing of the powders.
- For successful results in compaction and sintering, the starting powders must be homogenized
- Blending powders of the same chemistry but possibly different particle sizes are intermingled.
- Different particle sizes are often blended to reduce porosity.
- Mixing-powders of different chemistries are combined.
- PM technology allows mixing various metals into alloys that would be difficult or impossible to produce by other means.
- Compaction-pressing into desired part shape.
Application of high pressure to the powders to form them into the required shape, the conventional compaction method is pressing, in which opposing punches squeeze the powders contained in a die. The workpiece after pressing is called a green compact, the word green meaning not yet fully processed. The green strength of the part when pressed is adequate for handling but far less than after sintering.
- Sintering-heating to a temperature below the melting point to cause solid-state bonding of particles and strengthening of part.
Heat treatment to bond the metallic particles, thereby increasing strength and hardness, usually carried out at between 70% and 90% of the metal’s melting point (absolute scale), generally agreed among researchers that the primary driving force for sintering is reduction of surface energy Part shrinkage occurs during sintering due to pore size reduction.
In addition, secondary operations are sometimes performed to improve dimensional accuracy, increase density, and for other reasons.