Carbide Injection Molding Process

The problems in the MIM of Cemented Carbide, such as binder selection, the control of defects and the carbon content, sintering process, have been investigated in this dissertation. The results have shown as the following:The binder system of PW:79%,EVA: 10%,HOPE: 10%,SA:1%can meet the demand of the Cemented Carbide powder(the average size of 1.05 Mm ) selected in the experiment. The binder has better wetting qualities with the powder and the feedstock has favorable rheological behavior. The suitable solid loading is 58%. The injection temperature of the feedstock is slow and the binder can been removed by the step-by-step debinding.For the standard bending samples, the best injection temperature, the best temperature of mould and molding pressure are 130 癈 ,35-40 癈 and HOMpa respectively. For the adaptor of bayonet the best injection temperature, the best temperature of mould and molding pressure are 130 癈 ,38-42 癈 and lOSMpa respectively. The method determining ideal debinding process has been investigated, which is the combination of the pyrolysis data of the components of the binder, the TGA-DTA curves of the feedstock with the curves holding time at the temperature of the end of the pyrolysis data. After investigating carefully, the best debinding process is obtained. By a series of experiments, the author of the dissertation has get the optical sintering process, which is that in the sintering furnace with an air pressure of 65Pa ,10癈/ min rate is applied to 650癈 and hold for 30min, then a 10癈/ min rate is applied to IIOO'C and hold for 30min, and then a 6癈/ min rate is applied to 1460癈 and hold for 60min, finally the samples are cooled at 10"C/ min until 600 "C to reduce thermal residual stresses. This sintering process can obtain YG8 Cemented Carbide samples with high properties and homogeneous microstructure. The hardness, density, bending strength of the samples are 91HRA, 14.7g.cm"3, 2450 N.mm"2 respectively.The mixing of the feedstock of Cemented Carbide is easy to make oxygen content of the feedstock increase. The oxygen can react with carbon and lead todecarbonization of the samples. To make the feedstock homogeneous but not to make oxygen content increase, the best mixing temperature and time are determined, which is 125癈and ISOmin. The debinding atmosphere has great influence on the carbon content of the samples. In the H2 atmosphere, the decarbonization of the samples is serious. The decarbonization in the high-purity N2 atmosphere is less. Furthermore, the oxygen content and the dewpoint of the debinding atmosphere, the temperature and time of debinding all affect the carbon content of the samples. During the sintering process, preserving for SOmin at 650癈 can improve the carbide content of the samples.Adaptors of bayonets with complex shapes have been produced in the experiment. And the parts have better properties. Comparing with the traditional method of P/M of manufacturing Cemented Carbide, MIM of Cemented Carbide has more difficulties in controlling dimensional accuracy. But the dimensional accuracy can be improved in the future.