Understanding the Basic Conventional Powder Metallurgy ProcessSponsored Video | March 27, 2018
Conventional powder metallurgy (PM) components are used in automotive, lawn and garden, recreation, agricultural, hydraulics and other markets, due to their efficiency and consistency. 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. At this point, many components are considered finished and shipped to the customer; however, some components are then treated with secondary operations.
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 powder metallurgy. 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). MIM technology offers nearly unlimited shape and geometric-feature capabilities with high-production rates.
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.
PM components can be produced at rates from several hundreds 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.
Is Machining Possible?
In short, yes, machining is possible; however, with careful tool design, good process capabilities and CNC closed-loop control of compaction, machining can be made unnecessary. When machining is necessary, it is generally quite manageable since the close tolerance of PM dies and close control of powder choices has already minimized the need to machine the component.
To learn more about PM technology, from conventional press-and-sinter PM to MIM, additive manufacturing and more, or to seek assistance in locating PM component fabricators, please visit PickPM.com.