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Sintering might best be described as the synthetic manufacture of solid products using controlled heating of powdered raw materials. The proper application of sintering temperature results in the adhesion of the powder grains to each other without melting the material. This proper temperature is ordinarily 2/3 the melting point of the particular material. Sintering, though today a highly technological process characterized by CAD-systems, laser systems, and plasma systems, has its roots in the ancient method of firing pottery.
Sintering is generally used in the manufacture of ceramic products, however, the process can be used to fashion metal, glass, and plastic objects, as well as composites and alloys. As long as the raw material for a particular product is in a powdered form, the product can be sintered. The processes, of course, differ widely according to the molecular makeup and melting temperature of the powder grains, and the end use of the sintered product. Though, for instance, a plastic powder cannot be sintered into a metallic object, different powders, such as a ceramic/metallic mix can be sintered into a composite object.
There are two essential methods of sintered manufacturing: solid state, and liquid phase. As its name implies, solid state sintering is the fusing, or forming of powdered material into a product without actually liquefying the material. Conversely, the liquid phase process introduces a liquid step into the process of heating the powder grains. Liquid phase sintering is generally easier and more cost-effective than solid state. However, a certain degradation of the raw material will occur that is not the case with the solid state process.
In addition to the two basic sintering methods, a number of specific variations 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 former uses pulsed direct-current (DC) electrical charges to sinter the powder compact essentially from the inside out, and is quick and relatively inexpensive, while the latter method offers the ability to target particular sections of the objects produced to improve, incrementally, the density and porosity of the product.
Sintering has come a long way since the days when the firing of pottery was a state-of-the-art fired manufacturing process. The advantages of sintered products over stamped, forged, or molded products include higher purity of raw materials, the maintenance of purity through the manufacturing process, the stability of repetitive steps in manufacture, and the uniform density of the item produced. Obviously, advancements in technology ensure a more cost-effective manufacturing of higher quality sintered products.