silver+lost wax support material?

Discussion in 'Technologies and Hardware' started by MissStabby, Mar 27, 2012.

  1. MissStabby
    MissStabby New Member
    Currently i have a model that went in production to be casted in sterling silver.

    Though only recently i noticed that the model contained a few "unreachable" airpockets between a few meshes in my objects.
    When a wax model is printed, is the support material also made out of wax/meltable material or is the support material a powder that does not melt?
    Since i was wondering, if those area's can not be cleaned of the supporting material, will those act like the parts are solid?
    Or will the model eventually cave in and deform during the casting procedure?

    This got me curious about this type of "error",
    so to exaggerate the concept... take a look at this picture:
    [​IMG]

    In the printed model these would be complete a ball with a complete shell around them, completely closed. in the picture it's sliced open for illustrative purposes.
    Also think of it being printed at the smallest scale with the outerwall being less than the advised 0.6 mm thickness


    The "airpocket" between the core and the shell is completely unreachable and sealed off from the outside. Also the sphere and the core are not attached to eachother.

    Depending on how the process goes, i can think of 6 different outcomes:


    A. During casting the hollow room would be filled with waxy support material that acts as if the model is printed like a solid wax model.
    (so when sawing the sphere in half after printing+casting, will you get a solid ball of silver)

    B. When sawing the model in half you would see the inner core, dropped down and welded/molten to the bottom of the outer shell.

    C. The outer shell would warp and collapse during the casting process, ending the model up looking like a wrinkled raisin

    D. The outer shell would be removed by the support material cleaning, so you'd just have the inner sphere.

    E. The "airpocket" contains a nonmelting substance that will maybe drift upwards or sink downwards during casting

    F. The trapped air in the inside will form a air bubble on the top of the model, resulting in craters on the top most parts of the model



     
    Last edited: Mar 27, 2012
  2. stonysmith
    stonysmith Well-Known Member Moderator
    There is another answer, that unfortunately, you're not going to like. If the OUTER surface is completely solid, then Shapeway's MeshMedic is going to ignore all the rest of the shells, and only end up with the outermost surface.. none of the inner topology will be considered.

    In order to have the inner void as you've shown it, you must have a hole from the void leading thru to the outside. Depending upon the material, there are rules about how large that hole needs to be.

    Furthermore, for Silver, that inner ball has to somehow be connected to the outside. You can't have it floating as you've shown. There has to be a path somehow for the silver to flow from the outer shell into the inner ball.
     
  3. stop4stuff
    stop4stuff Well-Known Member
    As stony says.

    Consider a hollow space to be like a cave with an open entrance air can reach all areas of the cave because the entrance is open - its the same with Shapeways 3D printing, if there's no access to the inside, the inside is treated as solid.

     
  4. MissStabby
    MissStabby New Member
    nah that's something i'm going to like since then it would be fixing the airpockets.

    Though what would happen if they were "technically" not completely sealed off, but just near unreachable?

    like this situation:

    [​IMG]
    Note the impossibly thin walls at the top/bottom,
    would you end up with a crater on both poles?

    so is supportmaterial that is unreachable going to act just like a solid, or is the support material something that does behave completely different to the wax in the official model.

    similar to this example:
    [​IMG]
    The box is hollow on the inside, has opening to the outside, but through those holes it would be near impossible to reach inside to remove supporting material
     
    Last edited: Mar 28, 2012
  5. stop4stuff
    stop4stuff Well-Known Member
    Your ball example would probably get picked up on the manual chesks at order time - thin walls and moveable parts.

    The box example might be sent for printing in silver, it would depend on the size of the holes from, Silver Design Rules; "If you have multiple holes, each hole must be greater than 2 mm in diameter."

    All the materials have design rules, it is best to follow them :)


     
  6. GlenG
    GlenG New Member
    What is printable and what is lost wax castable are not always the same. A wax model needs to be embedded in refractory plaster before casting , this is the mold into which molten metal is poured. You cannot just float a core in a mold, it needs to be attached to the inner walls of the mold. Also, after casting the mold material is usually removed with high pressure water blasting. Anything that is "unreachable" will remain as a permanent feature of the casting and this is really not a good situation. I suggest you read up on casting and mold making to learn how best to integrate 3dp and casting.
    -G