Powder metallurgy is defined as the science, technology and art of producing metal parts from powders. The process involves blending fine powders of metals and/or other materials, pressing them into desired shapes, and then subjecting them to a high temperature heat treatment. This results in the formation of a solid, strong, and homogeneous part known as a “green part”.
Powder metallurgy (PM) processes are used to produce parts with a wide range of shapes, densities, and physical and magnetic properties, from very large (weights up to 30 tons) to very small (~100 µm) in size. Because of the flexibility of the process and its scalability, Powder metallurgy has many attractive features for manufacturers. The properties of the components produced by this technology also bring value to the end-user. The main advantages of powder metallurgy are that it is a low cost process and does not require the use of solvents or other consumables. Additionally, parts produced by PM generally require less energy to fabricate and have lower recoil forces when subjected to impacts than parts produced by traditional casting and machining processes.
Most Powder metallurgy processes can be divided into four major steps: powder preparation, powder compaction, sintering, and finishing operations. Beforehand, a suitable raw material must be chosen. This choice is governed by both the finished part’s requirements and the equipment availability. Powders for PM could be of pure metals, alloys, salts, oxides, etc.
One of the most important steps in the PM process is compaction. In this stage, the powders are deposited onto a die and then subjected to a compaction phase, in which their surfaces and their internal structures become closer and then form a homogeneous mass. Compaction can be done in two ways: cold pressing and hot pressing. In cold pressing, the powder is differentially compacted under great pressure without special heating. In hot pressing, the powder is heated up to a few hundred degrees Celsius in advance, allowing the powder particles to become plastic and thus filling the die more easily.
In order to achieve product properties of sufficient quality, the compacted parts must generally be subjected to a post-compaction heat treatment, also known as sintering. Sintering is basically the densifying of the compacted powder particles by heating them up to a temperature lower than their melting points. This process eliminates porosity and removes residual stresses from the part, improves the strength and homogeneity of the material, and increases the density of the part.
The last step of powder metallurgy process is finishing operations. Depending on the application, these operations could include machining, additional heat treatments, annealing and surface treatments such as plating, painting, grinding, and polishing.
Powder metallurgy technology is a mature and economically attractive manufacturing process for many kinds of complex components. In many industries such as automotive and aerospace, PM has become an essential technology for producing complex, high performance parts with tight dimensional tolerances and low environmental impacts.
