Discover the power of press-and-sinter powder metallurgy
April 19, 2019Conventional powder metallurgy (PM) components are used in automotive, lawn and garden, recreation, agricultural, hydraulics and other markets due to its design flexibility, efficiency and consistency.
A basic overview
The basic conventional press-and-sinter process begins by blending or mixing together metal powder(s) and lubricants. The press-ready mix is then compacted in a closed die and formed to the prescribed density.
Density, the weight per unit volume, determines a lot about the properties of a PM component. As component density increases via compaction, porosity decreases as the area of contact between powder particles is increased.
During the sintering stage, the powder particles are welded together in a furnace to form strong metallurgical bonds between the powder particles.
Are there size limitations?
Component sizes are limited by the equipment more than geometry; however, learning about aspect ratio (relationship of a component’s width to the height) will help you understand if your component is a good fit for conventional press-and-sinter PM. Also, a component that is not a good fit for conventional PM may be an excellent fit for another PM process like metal injection molding (MIM) or another PM processing technology. The best way to design a component is to involve a PM component designer early in the process.
Material choices with powder metallurgy
There is an extensive range of materials available for use with PM technology. Many PM-based materials found in industrial use include combinations of iron and other metallic, semi-metallic or transitional elements. The powders are typically mixed by combining pure elemental powders or are prealloyed so that each particle has the same chemistry. It is not possible to compact steel powder; therefore, the ability to mix elemental powders, specifically iron and graphite, makes it possible to compact steel components. Additionally, tungsten powder can be mixed with cobalt or other elements to “bond” the particles. It would be difficult, if not impossible, to process tungsten via any other method due to its high melting temperature.
Controlled tolerance
PM components can be produced at rates from several hundred to several thousands of parts per hour. The key elements of dimensional change include orientation, component size and complexity, run-out, powder formulation, tool wear, sintering and heat treatment, and secondary operations, such as coining and sizing. Radial dimensions are generally controlled by the dimensions of the tool. Tooling dimensions are consistent relative to what each part experiences during the compaction cycle.
Secondary operations
A sintered PM component can be finished or treated just like any other metal component; however, with careful tool design, good process capabilities and CNC closed-loop control of compaction, many secondary operations can be made unnecessary. Nevertheless, PM components can be machined, repressed, oil or resin impregnated, infiltrated, heat treated, finished with deburring or burnishing, and more.
To learn more about PM technology, from conventional press-and-sinter PM to metal injection molding and additive manufacturing and more, as well as for assistance in locating PM component fabricators, please visit PickPM.com.