Sintering is a process of heating powdered raw materials to create solid products without melting them. It can be used to shape ceramics, metals, glass, plastics, composites, and alloys. There are two methods: solid state and liquid phase, with specific variants like spark plasma and selective laser sintering. Sintered products have advantages over other manufacturing processes due to higher purity, stability, and uniform density. Technological advances have made sintering more cost-effective and of higher quality.
Sintering could best be described as the synthetic manufacture of solid products using controlled heating of powdered raw materials. The correct application of the sintering temperature results in the adhesion of the powder grains to each other without melting the material. This proper temperature is usually 2/3 of the melting point of the particular material. Sintering, although today a highly technological process characterized by CAD systems, laser systems and plasma systems, has its roots in the ancient method of firing ceramics.
Sintering is generally used in the manufacture of ceramic products, however, the process can be used to shape metal, glass and plastic objects as well as composites and alloys. As long as the raw material for a particular product is powder, the product can be sintered. The processes, of course, differ widely depending on the molecular composition and melting temperature of the powder grains and the end use of the sintered product. While, for example, a plastic powder cannot be sintered into a metal object, different powders, such as a ceramic/metal blend, can be sintered into a composite object.
There are two essential methods for sintered manufacturing: solid state and liquid phase. As the name suggests, solid-state sintering is the melting or forming of powdered material into a product without actually liquefying the material. In contrast, the liquid phase process introduces a liquid phase into the process of heating the powder grains. Liquid-phase sintering is generally simpler and cheaper than solid-state sintering. However, some degradation of the raw material will occur which is not the case in the solid state process.
In addition to the two basic sintering methods, some specific variants of these methods are also used in the production of sintered products. Spark plasma sintering and selective laser sintering are two of the methods used to sinter products to specific tolerances and specifications. The first uses pulsed direct current (DC) electric charges to sinter the powder compact essentially from the inside out, and is fast and relatively cheap, while the second method offers the possibility of targeting particular sections of the objects produced for incrementally improve the density and porosity of the product.
Sintering has come a long way from the days when firing ceramics was a state-of-the-art fired manufacturing process. The advantages of sintered products over stamped, forged or stamped products include higher purity of raw materials, maintenance of purity through the manufacturing process, stability of repetitive steps in manufacturing, and uniform density of the manufactured item. Of course, technological advances ensure more cost-effective production of higher quality sintered products.
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