Basic manufacturing process
Manufacturing a powdered metal component needs two basic elements: a metallic powder, and a tooling. Taking them, the basic process to produce a powdered metal part consists of three operations: powder mixing, compacting, and sintering.
The raw material of a powdered metal component is always a metallic powder. The powder chemical composition is chosen in order to achieve the material characteristics. Metal powders can be pure metals (iron, copper), or alloyed powders (bronze, brass, steel, etc.). The powder nature (sponge, irregular, spherical, laminar), can also give particular properties to the component.
The base powder is mixed with some alloying elements, depending on the final composition of the material (such as graphite, nickel, copper,…), with an organic solid lubricant (necessary to compact the powder), and sometimes with special additives. The result is a powder mixture with an homogeneous additive distribution. The chemical composition is of critical importance in order to achieve the mechanical, physical or chemical characteristics of the material, and it is ensured through strict dosing and control processes.
The tooling is a rigid element with the negative shape of the final part, so the powder mixture is pressed inside it. The tool is an element of a very high precision, and high durability. SMED techniques are used for the tooling assembly and maintenance.
The powder mixture fills the tool cavity by gravity, and an uni-axial pressure within 30 to 210 ksi is applied. The exact pressure depends on the final density to be achieved. The compacted part is ejected from tooling, and the result is a “green part”, which has enough mechanical strenght to be handled. The compacting process is statistically assured by SPC controls of the unique characteristics of the part.
Sintering is a thermal cycle consisting of heating the compacted part during a given time. Temperature is lower than the base metal melting point, normally between 1,300 and 2,400ºF depending on the material and the characteristics to be reached. The high temperature activates a solid-state diffusion mechanism, which leads to welding of particles between them, and to diffuse the alloying elements inside the base metal.
Sintering is done in continuous furnaces under controlled speed, and in atmosphere with controlled chemical composition.
The result of these basic operations is a metallic part with a certain micro-porosity, and high dimensional precision, which is perfectly functional when the obtained characteristics meet the component specifications.