3 Attachment(s)
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.
Attachment 294634Attachment 294636Attachment 294638
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:)
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.
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?
Re: ISSUE with thermoforming clear acrylic sheets
Marks are inside, where mold is.
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.
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?
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.
Re: ISSUE with thermoforming clear acrylic sheets
Quote:
Originally Posted by
spektr
To the mold and wipe it off
Did this help and solve the issue?
I am trying to vacuum thermoform a clear canopy from 3/16" cast Acrylic sheet. The female mold is made with fiberglass and high heat epoxy (500 deg F), we have 400 grit sanded surface on the mold. We heat the sheet in a frame and then taco the frame in the mold and apply a clamping ring around the frame and then put the whole mold into the oven for 18 minutes or so. When the temp reaches between 325 to 350 F, we apply 10 to 15 psi vacuum through a metal port on the mold. The vacuum port line is metal and sticks out of the oven. It takes a few minutes to deep draw (29 inches at the deepest), all the time the mold and sheet maintain between 325 to 350 F. Then we cool it with air flow while keeping the vacuum to 3 to 5 psi to maintain shape.
What I see are subtle rund golf ball like imperfections in the canopy specially where stretching has taken place it seems. If anyone has any ideas, I'd like to hear
Re: ISSUE with thermoforming clear acrylic sheets
Hello
We are producing abs sheets.
There are a few factors
1, abs sheet could be 2nd grade. Not as good as you think
2: it could have been waiting for too long. You have maximum 2 months to use it.
If you have a photo of the abs please post and i can address the issue
