Cemented carbide powder injection molding degreasing and carbon content control


Compared with machining and other traditional forming technologies, the biggest advantage of metal powder injection molding may be the shape freedom of forming parts the economic efficiency of manufacturing technology. Meanwhile, powder injection molding has a wide material range, for example, from ordinary metals to special metals that have high melting point and high hardness, as long as they can be made into powders that are suitable for mixing and pelletizing, they can all be used as raw material of metal powder injection molding.

Among them, tungsten carbide hard alloy is a kind of difficult-to-machine material that has high hardness and high melting point, which can only be made into parts that have large size and simple shape by using traditional machining methods. Regarding some cemented carbide parts that have complex shape and small size, by using traditional machining methods, it will have high production cost as well as products will have low uniformity. In recent years, with the increasing demand for complex shape cemented carbide parts, watch chain, wristwatch case, shaver, microbit, sewing machine parts and other complex shape cemented carbide parts have been more and more widely used in production and daily life.

high purity tungsten carbide powderMetal injection molding technology that can produce small size and complex shape metal parts also has been used in producing tungsten carbide hard alloy parts. However, as tungsten carbide hard alloy materials will be easy to decarburize in the machining process and will influence parts quality as well as powder injection molding has complex process and many influence factors, the degreasing difficulty can be regarded as one of the important influence factors for tungsten carbide hard alloy powder injection molding technology.

Therefore, this article will mainly introduce the way to select appropriate degreasing methods so as to better degrease and control carbon content of metal powder injection molding products. Among the numerous degreasing methods, thermal debinding and solvent degreasing are most commonly used. In the degreasing of cemented carbide injection molding products, these two methods will be used successively. By using solvent degreasing firstly, the binder composition that can dissolve in the solvent will be thoroughly removed from injection blank. After solvent degreasing, it will form interconnected pore channel inside blanks. At this time, by using thermal debinding, it can save more degreasing time and can shorten the whole degreasing cycle.

Tungsten carbide hard alloy injection blank will be easy to decarburize in thermal debinding under hydrogen atmosphere. This is because under certain temperature, the alloy composition of cemented carbide will have chemical reaction with water vapor in the hydrogen atmosphere, thus it will lead to decarburization. However, if we reduce temperature so as to avoid decarburization, the high-molecular polymer cannot be removed clearly from binders. Therefore, by using solvent degreasing + thermal debinding, it will have shorter thermal debinding time as well as will have higher carbon content in the degreasing blank compared with single thermal debinding.

It can be seen that the appropriate degreasing method will have significant influence on degreasing time and degreasing cycle, besides, it is also an important channel of controlling the carbon content of cemented carbide parts by controlling the decarburization phenomenon in the degreasing process. As the carbon content of cemented carbide degreasing blanks will be directly related with degreasing methods, it can effectively control carbon content of cemented carbide parts by using solvent degreasing method firstly and thermal debinding later.