Metal and Powder Measurement

Metal Injection Molding (MIM) and Particle Size Distribution / Specific Surface Area / Dry Density

Metal Injection Molding (MIM) is a new method of metal molding. Metal products with a complex shape, small shape and high precision can be manufactured since this method enables injection molding to be applied to metal in the same manner as plastic materials. Complex shapes made of titanium and other difficult-to-cut materials also can be molded. Furthermore, high strength on a par with solid metal can be obtained since intricate metallographic structures can be formed by sintering. The introduction of parts and components made using MIM technology is proceeding at a rapid pace in the fields of medicine, automobiles and optical communications.

The first part of the MIM process involves mixing and kneading metal powder and an organic binder, and injection-molding the resulting mixture. The molded part then passes through the degreasing process to remove the binder and then on to the sintering process.

Particle size distribution affects the fluidity of the material at the molding stage. And, in the degreasing process, the specific surface area of the particles affects the residual amount of organic binder.

Though final evaluation methods for MIM-molded parts have not yet been standardized, density is measured in addition to general mechanical strength (tensile test). To be more exact, density is assessed using "relative density," the ratio of the density of molding material to solid metal.

If material density is high, this means that sintering has progressed sufficiently and strength also has increased. High-quality MIM-molded parts exhibit a high relative density value of 90 and several percent, so dry density measurement must be used to achieve high precision.