Powder metallurgy utilizes metallic powders in the manufacture of shaped components which may be finished or semi-finished products. Also known as press-and-sinter processing, metallurgy is an increasingly common alternative to traditional casting from molten metal or forging at softening temperatures to create application specific metal parts.
Powder metallurgy heats metal components to temperatures just below the melting point in order to compress and combine them. Because no actual melting occurs, the powders keep their specific properties. These metal powders can be elemental, pre-alloyed or partially alloyed allowing for the creation of highly unique and, more importantly, highly specific metal compositions. Metals that are commonly used in powdered metallurgy and other powdered process include copper, iron, bronze and steel.
Automotive, biomedical, aerospace, energy, hardware, computer and electronics industries all utilize this technique. Specific products include powdered metal gears, medical implants, heat shields, magnets and fuel cells. Though not all, many of these items are fully formed with powdered metallurgy and require no secondary manufacturing. The inherent time and money savings of this process are compounded by its high material utilization. Approximately 97% of materials used in press-and-sinter processing end up in the actual parts themselves leaving only three percent as ‘in process scrap.’
There are three basic stages of powder metallurgy. First, the primary material, or materials, must be converted into powder. A number of machines are available for just this purpose. These mechanisms convert stock metal into powder, or finely divided metals, using techniques such as pulverization, chemical reduction, electrolytic techniques, mechanical alloying, atomization and flaking, with the later two being the most common. The powders are then injected into a mold or compact die. These provide the structural constraints for what the final product should be. As the molds are preformed, powder metallurgy is adept at creating intricate parts requiring bends, projections and depressions. The filled mold or die proceeds to the final stage, consolidation. As with the first step, there are a number of possible consolidation techniques to be used.
Possibilities include cold unaxial pressing, cold isostatic pressing, sintering, hot isostatic pressing, hot powder forging and metal injection molding. Each of these involves a great deal of pressure, though cold processes must apply considerably more pressure to obtain the cohesion possible in heated consolidation. The final result is a solid metal with variable properties and porosity. In addition to specific mechanisms used, considerations include choice of metal, size of the finished product and quantity. Powder metallurgy manufacturers can assist in making the decisions to create the desired product.