In this section, you use the Part Shrinkage command to estimate the percentage of shrinkage that occur based on the mold dimensions. Shrinkage is inherent in the injection molding process and occurs as the plastic melt in the part cools.
If necessary, adjustments can then be made to the mold dimensions until the part dimensions are within design specifications. Before running a shrinkage simulation, a material must be defined, and at least one gate location must exist.
- On the ribbon, click Core/Cavity tab > Plastic Part panel > Part Shrinkage
. - From the Part Shrinkage dialog box, select the Suggest tab and click Start.
- Click OK on the Analysis running dialog box.
- Review and take note of the results. The Results dialog box provides the following information:
- Nominal Dimensions: The original dimensions of the product.
- Shrinkage Allowance: Set to 0% by default, but you can define it.
- Mold Cavity Dimensions: Calculated by adding shrinkage allowance to nominal part dimensions.
- Estimated Shrinkage: The result of a shrinkage simulation based on mold cavity dimensions.
- Estimated Dimensions: Calculated by subtracting the estimated shrinkage from the mold cavity dimensions.
If the Estimated dimensions are close in value to the Nominal dimensions, the mold cavity dimensions do not need to be modified. If the Estimated and Nominal dimensions are not close in value, the estimated shrinkage values can be used to repopulate the shrinkage allowance. Or, the values can be manually adjusted before repeating the simulation. In this tutorial, the computed values are not acceptable. The simulation must be rerun, using the estimated shrinkage values as the shrinkage allowance.
- Click OK on the Summary dialog box.
- Click Yes in the Edit shrinkage dialog box to replace the current values. A Shrinkage node is created in the Mold Design browser.
- On the Mold Design browser, right-click the Shrinkage node shown in the following image and click Edit Feature.
- Notice the Shrink Percentage values are equal to the values obtained from the shrinkage simulation.
The range of shrinkage values is only an indication of typical values in the database and is not necessarily an acceptable value. Because they are based on processing conditions and part geometry, the simulation values could be slightly above or below these values.
- From the Part Shrinkage dialog box, select the Suggest tab, and click Start to rerun the simulation using the new shrinkage allowance values.
- Click Yes on the Analysis results exist dialog box.
- Click OK on the Analysis running dialog box.
- Review the results of the simulation. Notice that this time the Nominal Part Dimensions and the Estimated Dimensions are close. The mold cavity dimensions are now acceptable.
- Click OK on the Summary dialog box.
- Click Yes on the Part Shrinkage dialog box to replace the part shrinkage values.