shinkage on formed part

[ksupravan]

Hi.All
The PP formed part had some shrinkages. Why??
Would you give me some reccommend to fixing it?
Thank alot!

[DwightDixon]

When the material is in the mold it is close to its molten temperature. When you measure it is close to room temperature. All plastic materials shrink as they cool. Recut the tool to allow for this shrinkage. You are metal safe with all vacuum formed parts so this should be a minor expense.

[Mikey]

When the soft hot plastic forms over the mold it begins to cool & shrink. Like DwightDixon said you must enlarge your mold according to the shrinkage of that particular plastic. Check the shrinkage properties on MatWeb to get the shrinkage factor.

[DwightDixon]

I was thinking this was a female mold and a vac form operation. That is the more common process. I vac form you will be metal safe since you pull into the cavity and the finished part shrinks away from the cavity. If you have a male mold you are not metal safe and will have to increase the size of the male element.