Study On The Binder Applied To Metal Injection Molding

Metal injection molding is a new net shape technology applied to produce complex-shaped metal parts,in which materials are metal powder and binder. In this technique,the binder which are composed of low-melting-point component,main polymer and additives plays a key role. But it is not able to keep up with the development of metal injection molding that the binder can be obtained only in an experienced way. In order to solve the problem,this article has given a method to design new binder. And workable binder has been achieved.Firstly,according to the demand on the binder in metal injection molding and the relationship between polymers' structure and properties,the main polymers have been designed and synthesized. On the basis of careful analysis,we have selected methyl methacrylate and vinyl acetate which acted as main monomers,butyl acrylate and acrylonitrile which acted as auxiliary monomers. With these monomers,main polymers with different composition and different molecular weight have been prepared by pearl polymerization. By testing the viscous-flowing-point of these main polymers,we have found that the bind's shape-keeping was changed with the variety of the main polymers' composition and molecular weight,and shape-keeping can be satisfactory when the main polymers' composition and molecular weight are in a right position. Also,the binder's debinding has been characteristic of thermal analysis. It results that the content of methyl methacrylate monomeric unit in the main polymers must be sufficient,otherwise,the binder could not been debinded efficiently.Secondly,according to the theory of polymeric solution and the principle of compatibility,the low-melting-point component has been choosed. It is proved that polyethylene glycol 2000 can work well with the main polymers which has beenprepared. By blending the components in a high temperature,uniform binder has been attained. We have studied the fluidity of the binder,a conclusion has been drawn that the binder can provide ideal fluidity if the main polymers' composition and molecular have been controlled. Also,we have detected the interfacial adhesivity between the binder and the metal surface with the interfacial theory. It has been founded that excellent adhesivity came from good adaptation between the binder and the metal surface.Finally,overall analysis has been taken up on the shape-keeping,fluidity,adhesivity,and debinding. The ideal binder which can work well in many aspects has been obtained. It is that polyethylene glycol 2000 acts as the low-melting-point component,poly(methyl methacrylate-vinyl acetate-butyl acrylate) in which the monomeric unit composition should be 4:1:1 and the molecular weight should be near 25000 acts as the main polymer,and the weight fraction of the main polymers should be near twenty percent.