So between what I know of MJF 3D prints, using them in modeling applications rather extensively over the last few years, what I know of the material properties (especially a melting point), and the concept that some British organizations have been using to make castings with plastic cores that burn away as the molten metal is poured into the mold, I figured I'd pose the idea out loud... Well, in type anyway. If your average PA12 nylon or polypropolene base materials for MFJ melt around 350-370 degrees, and most of the metals that are used in castings are generally far hotter when molten, has any thought been given to using MJF printing technology to create patterns for parts needing casting?

You didn't really say what the application is. Brass/bronze type of metals, or ferrous castings? Decorative or structural?

You have a lot of options with 3-D printing. If you print with a hard enough material, you can print a conventional pattern that can be ram-molded in sand. I don't think you want to leave the plastic piece inside the mold when you pour the molten metal as the outgassing from the evaporating plastic would be a mess.

I have used a hobby grade printer and investment cast several hundred small (i.e., the biggest will fit into a 3" cube and the smallest was about twice the size of a grain of rice) parts and can only speak about my experience.

For investment casting you need to use a material which will burn out without leaving a lot of residue. I have used two printing processes. FPM printing using PLA filament and and MSLA using castable resin. Both are suitable using standard investment casting materials and processes. For the small parts I make, the castable resin gives more detailed prints and castings. Although the castable resin is more expensive, it's not a major factor for my small parts. At $75 per liter, I've found Siraya Tech Cast to be a good compromise between cost and casting quality. Many of the other lower cost resins either don't print well or don't cast well.

Castable resins cost two to three times more (and higher) than standard resin. I've tried using a standard resin to save money with poor results. It doesn't burn out cleanly and isn't suitable for investment casting.

The image is of a 3" diameter valve handle and u-joints for the turret valves for the Engine 557 restoration and some 1/4 scale examples for a model I'm building.

For large parts the resin costs might get prohibitive, but there might be room for hybrid patterns with the details 3D printed and used on large parts of expanded polystyrene.

Dylan, I'll message you directly.

Chris