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    Default ISSUE with thermoforming clear acrylic sheets

    I have plenty of small marks on the acrylic after its removed from the mold. It looks like it was caused by dirty/dusty mold, but mold is clean and smooth. I attached images of mold and acrylic.
    I am thermoforming clear and dark acrylic sheets thickness of 3/32". My mold is made of aluminum with almost mirror finish ( I tried few different finishes, but same issue). I heat my acrylic sheets to 250F and mold to 120F
    Can anyone help me what I am doing wrong?

    THANK YOU VERY MUCH.

    ISSUE with thermoforming clear acrylic sheets-image1-jpgISSUE with thermoforming clear acrylic sheets-image2-jpgISSUE with thermoforming clear acrylic sheets-image3-jpg

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    Default Re: ISSUE with thermoforming clear acrylic sheets

    Possibly moisture in the plastic? I know polycarbonate likes to be dried before you pull it.

    I get marks like that on the mold side of my hair cell ABS. I never tried to find out what it is because it's on the back side.

    Sorry I'm not much help but maybe that will rattle your brain



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    Default Re: ISSUE with thermoforming clear acrylic sheets

    Hi Derek.
    Its not moisture. I already tried to preheat it and dry it. I have experience with polycarbonate sheets and I know if its moisture you can see it right away while sheet is in the oven. I tried to heat the sheet up to 300F and just take it out from the oven to see if its moisture. Sheets were nice and clean without any marks.



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    Default Re: ISSUE with thermoforming clear acrylic sheets

    My guess would be a combination of trapped air pockets, maybe with moisture from the air, and dust attracted by static.... Acrylic is a total pain with static. Depending on the acrylic if might see something from manufacturer of the sheet. I had to use my rudimentary vac former as an oven for drape forming and on one piece I tried to reheat it had really funky blisters that I assume had something to do with how the sheet was made, mold release etc. I made a new part, although fortunately those pieces were not cosmetic in nature.

    Marks are on the inside (against the mold) or outside?



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    Default Re: ISSUE with thermoforming clear acrylic sheets

    Marks are inside, where mold is.



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    Default Re: ISSUE with thermoforming clear acrylic sheets

    I am not sure what type forms the best, but there are different types of acrylic with much different characteristics. When I first saw the pictures after you mentioned the mold was clean, I thought of static and dust particles. Maybe and air filter machine will help keep floating particles out of the air.
    I know for powder coating, I have my own booth built. You may consider building a booth around the forming machine. Even a temporary one or one with vinyl curtains would allow easier air filtration.

    Lee


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    Default Re: ISSUE with thermoforming clear acrylic sheets

    I am not sure what it is either.
    I know my friends dry the sheets in ovens for quite some time, before forming, are you drying your sheets?



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    Default Re: ISSUE with thermoforming clear acrylic sheets

    Ok, This problem is reasonably common with highly polished molds. They actually are too smooth to get all the air removed. My first move would be to go to the auto parts store and get a spray bottle of TIRE WET. This is a product I use to make the acrylic glide on tools more easily and kill bubbling. If that doesn't work, and it almost always does, take your mold to a glass bad booth and frost it up.



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    Quote Originally Posted by spektr View Post
    Ok, This problem is reasonably common with highly polished molds. They actually are too smooth to get all the air removed. My first move would be to go to the auto parts store and get a spray bottle of TIRE WET. This is a product I use to make the acrylic glide on tools more easily and kill bubbling. If that doesn't work, and it almost always does, take your mold to a glass bad booth and frost it up.
    Do you apply the Tire Wet to the acrylic or the aluminum mold?



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    Quote Originally Posted by seajai View Post
    Do you apply the Tire Wet to the acrylic or the aluminum mold?
    To the mold and wipe it off



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ISSUE with thermoforming clear acrylic sheets
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