The precipitation hardening stainless steel 17-4PH spur gear is manufactured by metal powder injection molding, and the following conclusions are obtained:
(1) Metal injection molding is similar to traditional plastic injection molding in that the material will produce shrinkage defects in the thickness direction of the product. Although the proportion of metal powder in the injection feed is 63.2% (volume fraction), and the thermal conductivity of metal solid is higher than that of plastic, during the cooling process, due to the uneven distribution of feed density and temperature loss, the distortion of the size head will inevitably occur;
(2) Using the compensation method of traditional plastic gear and the optimization of the inclined wire cutting die with electrode wire, the error can be effectively corrected, and the gear precision grade can be greatly improved. The precision grade of the spur gear injected by MIM can reach the level of AMGA Q9;
(3) The straight gear waist shrinkage phenomenon was not observed in the developed products. The main reason was that the equal thickness thinning design took effect, but the thinning design caused the deformation and distortion of the straight gear after sintering, but the traditional powder pressing process did not have this phenomenon. It is speculated that the geometric shape preservation problem of the gear was caused by the powder particle size and shrinkage characteristics, which must be further discussed;
(4) The precision grade of the developed small-module gear can reach AGMA Q9. Compared with the American Gear Manufacturing Association (ANSI/AGMA 2000-A88), this MIM gear product has exceeded Q9.
The direction of the improvement of spur gear mould in the future can be to use the same metal additive manufacturing method as plastic injection mould to make the annular conformal cooling system, which can quickly take away the heat of the solidification forming of the metal feed after injection, and reduce the distortion, including the problems of large and small ends of the outer diameter and bottom diameter of the teeth, the perpendicularity of the tooth thickness, and the shrinkage deformation. At the same time, the precision grade of the MIM spur gear can be effectively improved by cooperating with the mold compensation design.