I'm unsure what file formats those foundries that support patternless casting require. My guess is whether they use an additive e.g. multi-layer sand printing or subtractive (the milling process you describe) they would need to convert your DXF to and STL file. The little knowledge of these technique suggest most hobby machinists may find the costs eye-watering.

Or send STL to a foundry that can put your file into a 3D router and cut your pattern from foam then melt it out of the mould. Or 3D Cut from one of the PU boards made for pattern making and cast in the traditional way

Edited By JasonB on 08/08/2017 13:08:11

The direct 3D printing of the mould can give extra freedom of design as undercuts are possible (no pattern to withdraw) and no costs of making the pattern.

This page might give a feel for relative benefits of several routes. It is just one I happened to find on-line.

The answer may depend upon what you want to cast and its size. Working on the basis that you are competent with one of the 3D CAD packages you could go the route Neil suggests and get a pattern made in PLA and then either investment cast or burn it out as part of the process with sand casting. You need to speak to the foundry if you go the PLA route as they will have to be happy with the process and confident they will be able to get rid of any gas produced as the pattern is burnt out. The limit with this process is going to be the size of the item you want to produce and the ability to get the patten 3D printed.

You could go the ExOne route and get the sand directly printed. When I was looking to get the forks and headstock cast for my 6" scale steam roller the quotes were eye wateringly expensive.

The other method, which was the one I went for, was to use Polystyrene patterns. I emailed of an STL file and 4 weeks later collected some very big heavy castings. In this process the pattern is CNC machined from lumps of poly which are glued together to make the final item. Undercuts can be accommodated as can other features which would have traditionally needed a core box. Use one of the specialist companies as the process has its challenges and not all foundries will cast from poly patterns. Again getting rid of the gas as the pattern is burnt out can be a challenge and lead to porosity if not done properly. Finish could also be issue, if you need a good finish on as cast surfaces be prepared to put some effort in to cleaning the casting up.

Not mentioned here so far, you can have wax patterns directly 3D printed.

I have made several polystyrene patterns for one off castings. These have been burnt out with some success as only one out of about seven left an imperfection on the surface. Another advantage of making your own pattern is that you can see the final shape. Add a bit of extra machining allowance on critical faces.