After the heated plastic is injected into the mold it must cool before ejecting the final part from the mold. The shape of your part will effect how the part cools and must be considered during design.
The two key aspects to consider in cooling are:
- How long it will take to cool.
- How material will shrink, thereby effecting the accuracy and uniformity of your part after it cools.
Where the shape is thickest it will shrink the most. For example, in a 5 sided box with internal cylindrical posts for mounting a circuit board, you may see slight recess dimples on the outside of the box underneath where the posts occur as the posts will tent to pull the material in slightly.
Generally we recommend:
- Use an approximately uniform wall thickness throughout your design.
- Keep walls between .030" and 0.15". Walls up to 0.2" or slightly more are possible but not advisable.
- It should not be possible to fully hide a 0.3" diameter ball anywhere inside the material.
Often it is possible to take a solid shape that may have cooling issues and redesign it to be hollow to improve cooling. Sometimes this may requires making two hollow parts that snap or screw together to give the appearance of a solid part.