3D Printed Lost Foam Mold Inquiry

[vederstein]

I'm designing my next project: a 90°, double acting, two piston steam engine with a ø1¼ inch diameter piston and a 1 inch stroke. I wanted an oversquare engine for a higher speed because torque won't be that important. The purpose of this engine is to power a home built Spin Art machine for the 2019 Maker Faire season.

As I've done with my last steam engine, I plan on casting many components myself.

I was thinking about lost foam casting. I like the process, but my skills cutting with a hot wire cutter are rudimentary at best. So I had an idea: Could a 3D printer be used to create a mold to make the lost foam pattern?

The process would be as follows. The 3D printed clamshell would be assembled and insulation gap filling foam sprayed into the mold. After the foam is hardened, split the clamshell. The pattern would then be cleaned up and sprues glued on. Casting would be like any other lost foam process.

I think my idea is sound except what should I use for a mold release to keep the foam from sticking to the mold.

Has anyone any insights they would like to divulge?

Thanks,

...Ved.

 

[ThomasSK]

I can't see why your approach wouldn't work, but it seems to me to be a bit extra work that may be unnecessary unless you are going to make many of the castings.

If you print it with a regular PLA plastic, you can then do "lost PLA", the same way you do lost foam. I haven't tried it myself, but it seems to be quite popular on youtube.

As a alternative, I guess using the 3D print to replace the wax used for investment castings may work. Myfordboy on youtube to the rescue:

 

[vederstein]

My eariler experiments with lost PLA were complete and total failures. You can see my attempts of burning down my house in my other threads.

I had some luck with sand casting and home made casting sand. This method will be my fall back if this proposed lost foam method doesn't work.

I'm forging ahead and beginning my print of the first mold, the cylinder casting:

I'll run some experiments with this one and see if I have any luck with molding the foam before I go forth and multiply.

Thanks,

...Ved.

 

[lohring]

Gap filling foam is polyurethane. Burning it will release hydrogen cyanide. Lost foam uses expanded polystyrene. Otherwise 3D printing molds is a great idea. You can easily print both the patterns and core boxes for sand castings. If you need higher resolution, investment casting as mentioned above is the way to go. PLA is hard to burn out well. Machinable wax makes a wax filament.

Lohring Miller

 

[Cogsy]

I had one attempt at something similar and couldn't get it to work but that doesn't mean much. I coated the inside of a plastic mold with a thin coat of olive oil and filled with expanding foam. As I was concerned the foam would be too dense, or maybe burst the mold if I sealed it, I left the fill hole open so excess foam could escape as the expansion continued. So I'm not sure if the foam reacted with the olive oil or something, but once the foam had set and I opened the mold I found it almost completely empty. From memory the residue left in the mold did release but it didn't resemble my part at all. There wasn't enough left to even attempt a pour so I don't know how well it burns out either. I hope it works out better for you.

 

[vederstein]

I'll probably have the same issues as Cogsy. But damn it, I'm going to try anyway. At least I know I can go back to sand casting if required.

I'll do a couple of experiments with release oils prior to trying out the mold. I need to get some new filament. The filament I currently have sucks.

...Ved

 

[Cogsy]

Absolutely you should proceed - I'm hoping you get it to work so I can steal your process!

 

[vederstein]

As I was waiting for the first try of foam molding to cure, I created a short animation of the above engine. If anyone sees a major issues, I'm open to being notified.



Thanks,
...Ved.

 

[vederstein]

Results from the first try: Not Good. Awful really.

My crappy filament was too porous and the foam extruded into the mold itself. I tried using WD-40 as a mold release as well.

I did learn a couple of things:

1. Instead of trying to mold the entire piece, I think I'll try to mold halves and glue them together.
2. Instead of trying to come up with a mold release, I'll tuck in some cling wrap into the mold then pour the foam.
3. I need to get some better 3D printer filament (which should arrive in a few days).

 

[lohring]

Try burning a small piece of that scrap to see what will get with a pour that will burn a larger amount.

Lohring Miller

 

[Scott_M]

Maybe, try painting the mold to seal it, instead of cling wrap.

What kind of filament is that ? PLA ?

Scott

 

[Scott_M]

Hear is another question. Could you use your mold to pour wax into and then do lost wax ?

Scott

 

[Wizard69]

Most of my casting experience comes from years ago in the die cast industry so take this with a grain of salt.

The best 3D printing approach to cast metal would likely be the use of PLA with the investment casting process. That is print your structure with minimal infill. Cast vestment around it and when ready burn out the PLA. This should provide for excellent reproduction.

 

[rweber]

There is a filament made especially for this process. It behaves nearly like real wax, melts out well and without any residue. I used Modlay for this, but there are others.

 

[vederstein]

I have a roll of the printable wax. It's not very good. It doesn't print worth a damn. I consider it a waste of money. If you're printing small items (like jewelry), it works ok. But larger items are a go-no on my printer. This doesn't mean it works ok for other people, but I didn't have any luck with the parts I was trying to print.

I've tried the lost PLA method and had very bad, dangerous results.

Painting the inside of the mold may work and it's worth a try.

Thanks for the suggestion(s)...

...Ved.

 

[whitehouse260]

You might try acetone and normal styrofoam foam to make a putty and put that in the mold and let dry idk know if it will work though. Petg isn't affected by acetone.

 

[Anatol]

ditto Scott_M and rweber,
I did a bunch of lost wax casting. A very long time ago.
During plastic is likely to be poisonous at least.
Can you make a (two piece?) mold with the PLA and pour in wax?

 

[vederstein]

I did a bunch of lost wax casting. A very long time ago.

Did you cast the wax in plaster prior to burn out? What methods did you use? Do you have any pictures you'd be willing to share?

Thanks,

Ved.

 

[rweber]

Hmm, perhaps this is a printer related issue. I let my cores print by my Brother on this China low budget printer, and the result was very good.

The only issue here was, that the fins are not casted well because they are too thin for this kind of casting method. But gernerally this method worked well. I had no plaster , so I used some fine concrete which is normally used to compensate unevenness on the screed. I let it dry one day, turned it around and molt the wax-filement out in the oven. Then, turned it around again, put a riser and a filter on it and let the molten alu flow in.

 

[Anatol]

Ved
a VERY long time ago. No pics. Lost wax casting of silver jewelry. Small pieces, but not that much smaller than some model parts. I don't know if silver and gold have different flow properties in the mold than Iron or alu. I guess so. We used dental casting materials and techniques - but techniques used 40-50 years ago. The dental investment material gave very clean casts. It was centrifugal casting.; Buring out the wax also heated the mold., which in retrospect, I guess was a good thing. Wax makes it very easy to add vents and sprues etc. I *imagine* 3D printing mold pieces to cast wax form, then adding sprues and vents. I'm interested to see what you do.