About this result
Stress is created in the plastic as it flows through the mold. This stress is caused by friction between the moving plastic and the mold wall.
The shear stress should be less than the critical maximum value for that material, which can be obtained from the Material Database.
If a part has a yellow or red Quality prediction result, find out why. If it is due to high shear stress, try making some of the changes recommended below.
If the part is mostly green with some small yellow areas, it may be acceptable, but you should look carefully at the other result displays, to see exactly where and why the results went wrong.
Problems caused by high shear stress
High shear stress can cause cracks in the plastic, which can make the part degrade and fail.
What to do
Try to reduce the friction between the moving plastic and the mold wall by thickening the part, by reducing the plastic viscosity, or by slowing the plastic flow. These changes can be achieved by doing one or more of the following:
- Increase the mold or melt temperature to reduce the plastic viscosity.
- Thicken the part at the end of flow or in thin sections.
- If the injection time is longer than optimal, decrease the maximum injection time to make the plastic inject more quickly. This will increase the shear heating; as the plastic heats up, its viscosity decreases. If the injection time is already too low, decreasing the injection time can shear the material beyond its limits, compromising the mechanical properties of the finished part.
- Select a less viscous material (higher melt flow rate).