FOUNDRY TECHNIQUE

[CHARLES lipscombeParticipant @charleslipscombe16059]

I understand that there are foundries out there that can produce a part without a pattern, using a CAD drawing. Can anyone describe this process to me i.e. do I only need a DFX drawing?

Do these foundries start with a synthetic resin/sand block (or a waterglass/CO2 block) and just mill the cavity? In which case what are the limitations of the method (undercuts etc)?

Regards,Chas

[CHARLES lipscombeParticipant @charleslipscombe16059]

[Brian OldfordParticipant @brianoldford70365]

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.

[Neil WyattModerator @neilwyatt]

You might find the cheapest route would be:

• Export to STL
• Get STL printed in PLA by a 3D print company.
• Send pattern to foundry for 'lost plastic' casting.

[JasonBModerator @jasonb]

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

[Brian OldfordParticipant @brianoldford70365]

Posted by JasonB on 08/08/2017 12:33:54:

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 poly boards made for pattern making and cast in the traditional way

The OP mentioned undercuts which suggests any traditional/durable pattern would need cores/loose pieces or draw-backs. For "one-ofs" I have known people make consumable patterns (lost wax/foam) using manual methods.

If you know someone who'll print a PLA pattern for beer money, think Neil's suggestion may be the optimal route.

If the project is something others may want to have a go at, some of the costs of a durable pattern may be defrayed by extra selling castings on.

[David JuppParticipant @davidjupp51506]

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.

[MuzzerParticipant @muzzer]

Get yourself one of these.

Might struggle to get one in your garage. But seriously, there may be companies here that have them for small jobs? Looks like David Jupp beat me to it.

Murray

Edited By Muzzer on 08/08/2017 13:27:59

[AndyAParticipant @andya]

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.

[CHARLES lipscombeParticipant @charleslipscombe16059]

Thanks to everyone who has replied – most useful!

I make a small range of vintage/veteran motorcycle parts and I am trying to update myself with the latest techniques. Currently I use lost wax casting from aluminium/epoxy castings. I have tried lost wax from 3D-printed PLA but the first run was only partly successful due (according to the foundry) to porosity in the 3D prints. I am working on this through a local 3D printer but if this does not work, I am considering coating the PLA prints with a wax e.g. Carnuba wax car polish from an aerosol. All or any comments welcome please!

I also have a trial at the sand-process foundry, of a PLA pattern but this is on the basis of making an impression in the "sand" from the PLA pattern. The pattern is not consumed in this process so it can be used multiple times. Unfortunately the local foundries are glacially slow so it will be a while before I know how these ideas will work out.

Best wishes to all, Chas

[David JuppParticipant @davidjupp51506]

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

[Paul LousickParticipant @paullousick59116]

Wax filament is available for printing 3D models which can then be sanded, cut, machined and then used tor casting in metal using the lost wax process. (Without having to use it as a master to make a mold)

PLA has heen tried but does not completely melt out of the mould or leaves a residue in the mold which effects the casting.

I have a numger of valve components which have to be cast in bronze and is the main reason that I have just purchased a 3D printer. Paying someone else to 3D print a model is expensive ! Just have to assemble it and get it going.

Paul.

**LINK**

[Chris Evans 6Participant @chrisevans6]

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.

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