Precision Plastic Gear Mould Design

 1. Cavity design

          The cavity design of plastic gear molds has always been regarded as a technical problem in the mold industry. There are two main reasons for this: First, the plastic shrinkage rate is difficult to be precise: during the plastic gear molding process, the plastic is transformed from a granular solid raw material to a molten plastic liquid at high temperature, and then cooled to form a solid plastic gear. product. The shrinkage rate of plastic in this process is a range value, and it is difficult to accurately determine the shrinkage rate value of the plastic; the second is the nonlinear shrinkage calculation of the mold cavity: for the involute small modulus plastic gear mold, the mold cavity Actually an imaginary gear. This imaginary gear is different from both the displacement gear and the internal gear. This imaginary gear becomes the plastic gear we want after shrinking. The shrinkage of the imaginary gear on its involute tooth profile is different from the proportional shrinkage of the general plastic parts in all directions. On the gear plane, the shrinkage in the x and y directions is not equal, which is a nonlinear shrinkage, as shown in Figure 6. It is this nonlinear shrinkage that greatly increases the difficulty of designing the cavity of the involute plastic gear mold