1. Some Background concepts about the plastics gear mold building:

• the preferred resin used for plastics gear: POM,PA(PA46),PPA,PBT,PC,PPS,LCP.

• The class used in actual mold building is 3,4 and 5(JIS Standard).
• the bigger the outside diameter/teeth thickness, the more difficulty it’s to meet the specification/accuracy.
• For the steeped gear part, it’s preferred to design the gear ring at one single mold half(that is all the tooth was molded either cavity or in core side);
• 3 pin point gates per part  should always be employed to get a balanced filling to control the deformation/warp;
• the gate location should be placed near to the part center(not too close to teeth);
• the insert for teeth should be a round shape in most case and the Concentricity & Roundness error should be less than 0.005mm;
• the rib should be equally spaced and towards the head or bottom of teeth, not the side of teeth;
• the thickness of rib or boss feature should be less than 2/3 of averaged wall thickness;
• the highers the gear class, the smaller the mold cavitation: the general rule: class 3 & class 4: 2 & 4 cavity, class 5: 4~16 cavity

2.The shrinkage amount is different at the top diameter, pitch diameter and root diameter because of an nonlinear shrikaging , so a profile correction must be done to the 3dD model applied by an theory shrinkage value.

3. the orientation design  of gear teeth insert:

4.A typical spur gear mold design:

5 .A typical helical gear mold design: