WSF "not suitable for molding"?

Discussion in 'General Discussion' started by maketshi, Dec 30, 2011.

  1. maketshi
    maketshi New Member
    I want to make silicone molds from my parts, is that not practical with WSF? Why is WSF not suitable for molding?

    Could I use a sealer or primer to resolve this issue?

    Are all the other materials fine for molding?

  2. Youknowwho4eva
    Youknowwho4eva Shapeways Employee Community Team
    Any of the WSF materials would have to be sealed before using for a mold. They are very porous so you probably wouldn't be able to easily remove the silicon. I'd say any of the Detail materials would be better, but you may still need to polish, and maybe a light sealing to get any crevasses that are in the model.
  3. abby
    abby New Member
    It really depends what you intend for your castings.
    I have made many silicone moulds from WSF , some sealed and polished , others just as it comes.
    I havent experienced any problems removing patterns from moulds but I would be very careful if using FUD.
    I have had several sticky uncured spots whch I believe to be poisoning from the support media , or loose print material.
    No amount of washing and scrubbing has cured this problem and I have literally had to scrape each surface before spray painting with primer.
    After consultation with my rubber supplier I have now found a satisfactory solution.
  4. maketshi
    maketshi New Member
    Yeah, I was worried about poisoning the silicone.

    What was the solution you found?
  5. abby
    abby New Member
    Over 20 years or so I have tried many types of rubber including natural , polysulphide and urethane but have found silicone to be the most generally useful from a cost and convenience perspective.
    Some of my moulds are many years old and still good enough to use
    Having used silicone rubber from every major manufacturer , and here's a tip , most will give you a free 1 kg sample , if they won't then don't buy it.
    I have settled with Dow Silastic M.
    This is a clear silicone that cures in 8-12 hours and , up to now , shows good resistance to poisoning.
    One drawback is that you must allow lots of room during degassing as it expands twice as much as any other I have used.
    Even after degassing there will be one or two reluctant air bubbles so fill moulds very gently from a corner , allowing the flow to cover the master and prick any that might adhere because they don't want to rise easily.
  6. maketshi
    maketshi New Member
    Unfortunately, I don't have any degassing equipment. This is a kitchen table scale project. I've been using OOMOO 25 from Smooth-on because it doesn't need degassing, and can be demolded in 75 minutes..

  7. maketshi
    maketshi New Member
    New FUD parts arrived last week.

    Tried a thin test coat of OOMOO 25 silicone to check for cure inhibition. There was none as far as I could tell, but the silicone was kind of clingy to the porous FUD surface. I'm going to do another test today using a mold release.