The Development of P/M Complicated Shape Helical Gears

Recently, powder metal parts have been used in a lot of automobiles. One typical powder metal part is a helical gear. Compacting helical gears is much different from conventional compacting, because a part of the tool rotates on its own axis. The important points are as follows: (1) how to guide the upper punch into a die smoothly and to fit in it, (2) how to rotate the die/punch smoothly in order that the part of gear trains may not be broken by twisting stress during pressing process and (3) how to prevent green compacts from having crack/lamination. The larger the helix angle, the more difficult its compacting. The compacting of complicated shapes such as helical gears with an irregular shape or another helical gear is more difficult.

Powder metal helical gears are produced because powder metal is suitable for mass production at low cost. Most powder metal helical gears are simple shapes such as helical gears only outside or inside. The conventional tool set consists of a die and a corerod and an upper punch and a lower punch. A die or corerod and upper punch rotates on its own axis.

This paper reports the development of powder metal complicated shape helical gears. This reports the principle of helical gear compaction in the first section and the development of tool set and tool shape and manufacturing process of complicated shape helical gears in the second section.