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Thread: Storage Box Lid Warpage

  1. #1
    Join Date
    Nov 2013

    Storage Box Lid Warpage

    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 ?


  2. #2
    Join Date
    Aug 2019

    Re: Storage Box Lid Warpage

    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.

  3. #3
    Join Date
    Aug 2011
    Upstate of South Carolina

    Re: Storage Box Lid Warpage

    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.

  4. #4
    Join Date
    Nov 2013

    Re: Storage Box Lid Warpage

    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.

  5. #5

    Re: Storage Box Lid Warpage

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

  6. #6

    Re: Storage Box Lid Warpage

    Running 4 barrels 3 stations 3 different plastics bored question welcome

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