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I have a 3D printer and I have printed some models with castable resin. When I burn one of these models in the oven and then do the metal casting, the surface of the metal piece is not smooth.

I did a test with a pan. I put a model of wax and a model of castable resin to heat in a pan, and the wax model melts, but the resin model don't.

The resin I have is the following:

enter image description here

What is the correct process to make a correct resin casting?

Thanks for your help.

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  • $\begingroup$ Welcome to 3dPrinting.SE! $\endgroup$ – Pᴀᴜʟsᴛᴇʀ2 Mar 31 '19 at 0:01
  • $\begingroup$ Use silicone mold. $\endgroup$ – Fernando Baltazar Mar 31 '19 at 2:01
  • $\begingroup$ What temperature you burn your mold out at? $\endgroup$ – Trish Apr 1 '19 at 12:17
  • $\begingroup$ @FernandoBaltazar silicone molds are not useable for most metals. $\endgroup$ – Trish Apr 1 '19 at 12:17
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Factually, the correct process is to heat up the mold hot enough to evaporate the positive.

In investment casting the process to remove the wax or plastic positive is called the "Dewax" and "Burnout preheating".

The answer to your question depends on the material you use to generate a negative mold of the positive product. E.g. many silicate based materials require up to about 1100 °C to fully burnout all residue before pouring in the liquid metal.

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  • $\begingroup$ Wax for molding is usually melting low enough to melt out in a pan, unlike resins $\endgroup$ – Trish Apr 1 '19 at 11:39
  • $\begingroup$ @Trish That is why they need to burn out, oxidize. This requires very high temperatures. This is very commonly done nowadays as it is way cheaper and lead times are way shorter. This is a nice article. $\endgroup$ – 0scar Apr 1 '19 at 11:51
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Traditional lost molds.

The reason many jewelers use wax for making the molds for lost mold casting is, that it has (compared to plastic molding materials) a very low melting and boiling point, allowing to create molds with much lower temperature equipment.

A variant of green sand casting is done with materials that very quickly decompose in contact with the molten metal or that burn out after setting fire to them. Very common in this context is foamed styrene. Styrene melts and burns easily so it is easy to use in this way.

PLA has been used in some experiments as a positive and then molten out in a baking oven. It and other printing filaments are usually thermoplastics, so melting them out is similar to wax.

Resin is not soft wax or a thermoplastic.

No, in fact, most resins are a duroplastic, meaning that they don't melt.

If you print a positive from resin and then make a mold from that for lost mold casting, you go the traditional way. But most resins don't melt out the way wax does, and on contact with molten metal don'T evaporate the way wax residue does. You got to properly burn out the remains of the cured resin at a higher temperature and for a longer time than the wax as the melting point is much higher - use a proper burning oven. A proper burning oven in this relation reaches something like an email oven (1100 °C) or a clay burning oven (up to 1800 °C)

Putting the molds with the opening down into one of these ovens at high temperature should help a lot. Make sure to put a spacer and a tray below to allow better airflow and get the resin out.

Chemical Club.

Besides heat to destroy the resin, most resins could be solved by very highly aggressive chemicals. Which chemical works highly depends on what the resin actually is - if it is epoxy resin it would be the highly toxic CH2Cl2 while polyester resin is soluble in isopropanol and sulphuric acid.

Cold alternative?

If your product is to be made of a two-component resin or a ceramic that can be shaped cold and that sustains form, then you might also look at silicone molding. This is not an alternative for most metal castings. Among the very few exceptions is pewter, as PunishedPropsAcademy and Evan&Katelyn showed in their video and there are high temp silicones around that could be used repeatedly for pewter.

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