High density copper-based powder injection molding parts can be obtained by using redox copper powder

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Powder injection molding technology can be used in producing parts that have high quality, high uniformity, high density and high dimensional precision, which has been widely used in metal parts manufacturing field.

In copper-based powder injection molding parts production process, it will usually contain 50 percent or 10 percent (the volume fraction) of binders. Even after degreasing, a certain amount of binders will still exist in the parts, thus the oxide on the surface of copper powder will be reduced by these residuals.

copper metal powderHowever, if the oxidation degree of copper powder is too high, it will still be difficult to remove most of the oxidation pollutants even by using hydrogen reduction effect at 500 degrees Celsius in the sintering process. Besides, under this condition, the injection molding copper billet will have low density after degreasing and sintering. Copper powder that produced by oxide reduction method will have low price and fine particle size, but it will have irregular shape and high oxide pollution load; while the spherical fine powders that made by gas atomization method will have low oxide pollution load, but they are very expensive. In order to reduce the production cost and make sure that copper-base parts have good surface characteristics, it is very urgent to study oxide reduction copper powder method for injection molding technology.

In order to obtain high density copper-base metal powder injection parts, it is very important to properly control temperature in the sintering process. In the early stage, the sintered density will become higher and higher with the increasing of sintering temperature, however, when the density has reached up to 87 percent of the theoretical density, the density will decrease to some degree with the increasing of sintering temperature. Regarding the fine powder, it will have high density under low sintering temperature, but will have low final density under high sintering temperature.

The final sintered density of copper metal powder will depend on the comparative degree of surface oxidation. Besides, the oxidation reduction treatment is needed in the sintering process before the closing of holes. According to the latest researches that made by the industry experts, holes will begin to close under 85 percent of theoretical sintered density and will completely close under more than 95 percent of density. Generally speaking, before the closing of holes, most of the oxides should be reduced at less than 900 degrees Celsius. On the contrary, by preserving the heat for 2 hours under hydrogen atmosphere at 700 degrees Celsius, it can effectively reduce the residual oxide on the surface of copper powder.

In conclusion, in order to obtain high density copper-base powder parts by oxide reduction copper powder method, temperature should be strictly controlled and relevant parameters of oxidation reduction treatment should be well mastered.