Powder metallurgy (PM) is a metal processing technology in which parts are produced from metallic powders. In the usual PM production sequence, the powders are compressed into the desired shape and then heated to cause bonding of the particles into a hard, rigid mass. Compression, called pressing, is accomplished in a press-type machine using tools designed specifically for the part to be manufactured.
Principle of Powder Metallurgy
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Powder metallurgy is the process of blending fine powdered materials, compacting the same into a desired shape or form inside a mould followed by heating of the compacted powder in a controlled atmosphere, referred to as sintering to facilitate the formation of bonding of the powder particles to form the final part.
Thus, the powder metallurgy process generally consists of four basic steps, as indicated in Figure which are-
- Powder manufacture,
- Blending of powders,
- Compacting of powders in a mould or die
Compacting is generally performed at room temperature and at high pressure. Sintering is usually done at elevated temperature and at atmospheric pressure. Often, compacting and sintering are combined. Optional secondary processing often follows to obtain special properties or enhanced dimensional precision.
Also read: Solid state welding
Powder Metallurgy route is very suitable for parts that are required to be manufactured from a single or multiple materials (in powder form) with very high strength and melting temperature that pose challenge for the application of casting or deformation processes.
The tooling, which typically consists of a die and one or more punches, can be expensive, and PM is therefore most appropriate for medium and high production. The heating treatment, called sintering, is performed at a temperature below the melting point of the metal.
Advantages of Powder Metallurgy
- Parts can be produced in mass production using this technique.
- Very little waste of material; about 97% of the starting powders are converted to product.
- Parts having a specified level of porosity can be made. This feature lends itself to the production of porous metal parts such as filters and oil-impregnated bearings and gears.
- Certain metals that are difficult to fabricate by other methods can be shaped by powder metallurgy. Tungsten is an example; tungsten filaments used in incandescent lamp bulbs are made using PM technology.
- Certain metal alloy combinations and cermets can be formed by PM that cannot be produced by other methods.
- PM compares favorably with most casting processes in terms of dimensional control of the product. Tolerances of _0.13 mm (_0.005 in) are held routinely.
- PM production methods can be automated for economical production.
Disadvantages of Powder Metallurgy
These include the following:
- Tooling and equipment costs are high
- Metallic powders are expensive, and
- There are difficulties with storing and handling metal powders (such as regradation of the metal over time, and fire hazards with particular metals).
- There are limitations on part geometry because metal powders do not readily flow laterally in the die during pressing, and allowances must be provided for ejection of the part from the die after pressing.
- Variations in material density throughout the part may be a problem in PM, especially for complex part geometries.
Definition of Powder
A powder can be defined as a finely divided particulate solid.