Dies for pressing metal powders to form helical gears

摘要

This work concerns the realization of dies to produce helical gears by metal powder compaction. Due to the helicoidal geometry of the cylindrical gears, the punch, in addition to the axial motion, must necessarily rotate to "cross" the die. The innovative idea is to design a perfectly functioning system that can generate any helix angle (β) in the range of interest 0°-30°, using the simple contact between punch and die cavity during the rotation. First of all, the punch-die system was treated as a self-locking screw to determine the maximum β-value at which punch could be clamped inside the die during pressing. The analysis encouraged the execution of experimental tests related to a die with β = 5°, obtaining excellent results. Subsequently, FEM (Finite Element Method) analyses were performed on the static behavior of the die, subjected to the pressures exerted by powder and shrink-fitting ring, for three different β-values: 5°, 18° and 30°. The results obtained for the latter two angles were compared with those related to the die with β equal to 5°, considered valid thanks to experimentation, in order to theoretically verify the correct functioning even of dies with larger angles.