Storage Box Lid Warpage

[jonturka]

Hello All,
I agreed with a company for manufacturing series of storage boxes.
Numbers are too high, therefore cycle time is important.
We did initial trials of molds without any cooling. All lids have warpage as in the pictures. Wall thickness is 0,8 mm.
I assume this is due to anisotropic shrinkage.
Material is Random Copolymer.
Do you have any recommendations for injection molding of these parts ? Like;
Different cooling temperatures for different side of parts ? If so, how it must be ?
Any nucleating agent to reduce this warpage without losing the transparency ?
Any post molding method ?

https://www.imageupload.net/image/SfILK
https://www.imageupload.net/image/SfPU8
https://www.imageupload.net/image/SfEhd

Thanks

[iamplwirtz]

Cycle time too short. Cool the B side of the mold. Longer hold time in mold before ejecting. If you still have warp, create fixture to decompress part for a few minutes with fan on part so it cools without twisting.

[rickbatey]

I think you will need a short and quickly ramping downward hold pressure profile to stop this tendency. The root cause is as you said. I think a warmer mold on both halves to reduce molded in stress as well.
Now I want to know do you Mold the bottom half too? If so, I would use them as shrink fixtures and have operator put lids on bottoms ASAP after they come out of the mold. This reduces warp BUT ensures that lid and bases always match one another for fit.
BR,
Rick

[jonturka]

Hello Rick,
Nice to talk to you again after long time.
I will try different cooling profiles to solve problem.
I will mold also the bottom part. This is a good method. But disadvantage of this method is, I will lose the possibility of working and stacking with robot.

[Givemeacc88anyday]

Chiller might help will need 2 decompress a bit at feed 2 help get screw moving before trying 2 push thru cold mold

[Givemeacc88anyday]

Running 4 barrels 3 stations 3 different plastics bored question welcome

[joeprocess]

Is the warped corner always the same corner?