Powder metallurgy converts metal powder into solid objects using high pressure and temperature. Powder is made through crushing, grinding, or atomization. The powder is then compressed in a mold and strengthened through sintering. Hot isostatic pressing combines compaction and sintering.
Powder metallurgy is a process that involves converting powder into a solid object. Usually, the powder is a type of metal, such as iron, and the object to be made is usually shaped with a mold or casting. To form and fabricate metal objects through powder metallurgy, extremely high pressures and temperatures are required. Sintering, a heating process, and metal injection molding are commonly used techniques in powder metallurgy.
The first step in powder metallurgy is to convert the raw material into a powder form. Crushing, grinding, and using chemical reactions are common ways to make powder. Atomization is a technique in which material is melted into a molten liquid and forced through a small nozzle or tube at high speed. This causes the liquid to separate into individual droplets as it exits the tube. The droplets are collected and allowed to harden, resulting in fine, grain-sized particles.
Once the powder is produced, it is compacted in a high pressure mold. Usually, the powder is poured into the mold and a pressure plate is lowered to compress it. The resulting object is ejected from the mold. Typically, the pressure ranges from 80 to 1,000 psi.
Another method of compressing powder is called isostatic powder compaction. This technique uses a flexible mold that sits inside a pressure mold. The powder is placed in the flexible mold, while a machine delivers pressurized liquid or gas to the pressure mold. Pressure ranges from 15,000 psi to 40,000 psi. This method does not require lubricants when the powder is compacted, but standard mold compaction does. Subsequently, the object is strengthened by sintering.
Sintering is a heating process that bonds individual metal powder particles together. It usually takes place in a sintering furnace, where the temperature is set just below the melting point of the metal. This method is commonly used in the production of pottery. The process was patented by AG Bloxam in 1906, but there is evidence that the practice of fusing metal powders into solid objects has very ancient origins.
Some methods combine powder compaction and the sintering process, such as hot isostatic pressing. The process typically involves the use of pressurized argon gas and temperatures between 900°F (480°C) and 2250°F (1230°C). The powder is simultaneously compacted and sintered, saving time and material. This method also produces thinner walls and larger parts than standard powder compression methods.
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