Question about lost PLA casting

[werowance]

question about lost pla casting - often i will use red filler primer or heavy scratch primer to get rid of the print lines and make a smooth looking 3d print.

will that stuff burn out with the pla in my mold or will it leave a shell like a sheetrock mud coat might do ? thought about just plain parifin wax and painting it on the outside however i have warped pla prints with hot wax before so wanted to use the primer if it will burn out.

want to use plaster as the mold material, burn out the pla and hopefully the primer as well.

 

[GreenTwin]

I would use caution in burning out thermoplastic, due to how toxic the fumes can be.

I am not sure if a primer would burn out or not.
One way to find out; test it on a small part.

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[werowance]

ok, and on the burn out, ill do it on one of my old bbq grills or in the little toaster oven outside. i have plenty of a constant breeze flowing

 

[lee webster]

I watched several videos recently by Ingot Joe. He printed in PLA and used an oil bound sand. He left the 3D print in the sand and used a blowtorch to melt out the PLA before pouring. It seemed to work. He also tried pouring molten metal directly on to the PLA, and as he says himself, "it did not go well"

 

[Nerd1000]

You need fairly high temperatures to burn out successfully, more than 400 degrees C I think. I've done it by putting the moulds in the foundry for a while, this of course burns a lot of fuel.

If you don't get a complete burnout, your molten metal will do it for you... creating a huge amount of gas, and thus either a misrun or really bad porosity in the casting, or both! I found this out the hard way when trying to lost wax cast bronze jewelry, there were some very impressive flames shooting out of the vents and lots of bubbling in the sprue. The castings were of course total garbage, none of them filled the mould fully and the metal was so porous it was almost foam.

 

[creast]

From my experience I would try to avoid using fillers apart from wax which I sometimes use applied with a brush.
Best to do test to see what ash content you get.
Burnout should be done in a controlled electric kiln/furnace in slow ramped stages to at least 500C, 600-700 Deg C is better.
If you don't ramp up slowly you will have problems with cracking.
After burnout I use gentle air pressure to blow any ash out.
Only use proper refractory plaster.
Sanding PLA is a nightmare but a sure way to reduce layer lines.

 

[GreenTwin]

Having gone to the trouble of printing a pattern, and then filling and sanding it, I would be tempted to just use it to make traditional green sand or bound molds, and have a reusable pattern.

Lost PLA/lost foam seems to be all the rage these days, but I don't seen the logic in it in most situations.

I have seen some effective applications of lost PLA where there was an intricate part, and a large number of PLA prints were glued to a tree, and thus many parts could be made at the same time.
For a non-intricate part, there is nothing to be gained by going the lost PLA/lost foam route.

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[creast]

Agreed. It is a very useful method for small or detailed parts but is very time consuming.

 

[Shopgeezer]

There are PLA varieties made specifically for lost PLA casting. They have low ash and burn out more easily. I have heard that some are very soft and don’t make good prints. Good reports on others. Check this out on Amazon:

Polymaker PolyCast Filament 1.75mm for Investment Casting 750g Cardboard Spool - 3D Printer Filament for Lost Wax Investment Casting, Similar to Wax Filament for Metal Casting Plaster Cleanly Burn Out https://a.co/d/5J3QGSH

 

[timo_gross]

I wonder how much work it is to hand sand the PLA print before casting?
Or ist it possible to sand blast the PLA to get rid of print lines?
Maybe a quick sand blast of the metal part can remove the "print lines"?

 

[GreenTwin]

I have found the PLA lines in castings to be surprisingly deep.
They can be buffed off with a sanding sponge in a die grinder, but it takes more work than you may think, and requires removing more matierial than you may expect.

For a small part, you may need to allow for the removed material in the size of the printed pattern.

.

 

[GreenTwin]

There are PLA varieties made specifically for lost PLA casting. They have low ash and burn out more easily. I have heard that some are very soft and don’t make good prints. Good reports on others. Check this out on Amazon:

Polymaker PolyCast Filament 1.75mm for Investment Casting 750g Cardboard Spool - 3D Printer Filament for Lost Wax Investment Casting, Similar to Wax Filament for Metal Casting Plaster Cleanly Burn Out https://a.co/d/5J3QGSH

I would not purchase a large amount of the clean burn out material before trying it.

I have heard some issues of water absorption, if I remember correctly, but check me on that.

.

 

[creast]

There are PLA varieties made specifically for lost PLA casting. They have low ash and burn out more easily. I have heard that some are very soft and don’t make good prints. Good reports on others. Check this out on Amazon:

Polymaker PolyCast Filament 1.75mm for Investment Casting 750g Cardboard Spool - 3D Printer Filament for Lost Wax Investment Casting, Similar to Wax Filament for Metal Casting Plaster Cleanly Burn Out https://a.co/d/5J3QGSH

I have found standard PLA works just fine so no need for the added expense.

 

[Steamchick]

All this gets a big "WOW!" from me. All I have done (apart from casting lead fishng weights) is using Plaster of Paris simple moulds with aluminium or MAZAK scrap re-melted. Mu patterns were bits of bar-stock, wood, wax or whatever making a shape to make a lump of metal for machining.
Keep up the interesting posts, guys.
K2

 

[GreenTwin]

Back when I started learning foundry work, I purchased some Zamack, thinking that it would work much better than 356 aluminum due to its "lower melting point".
As it turns out, practically speaking, there is no significant difference between the melting temperature of zamak and the melting temperature of 356 aluminum, especially with regards to the burner output and the crucible used.

And the zamak just melts in front of a drill bit, and so it basically useless to me for engine work.
I can drill gray iron with no cutting fluids.

Zamak does have nice mass to it, and I hear it wears well too.

.

 

[Vietti]

I have had really good luck with ZMAC, it melts at around 700 f, I think Al is nearer to 1200. Drills and machines great and no sign of melting when drilled or turned. I melt it in an electric pot made for melting. lead. The neat thing is you can use segmented aluminum molds with proper coatings.

I wonder if you had a good alloy or were using scrap? I think it is under-appreciated in the hobby.

 

[GreenTwin]

I had some good Zamak ingots, but drilling it just seemed to cause it to melt in front of the bit.
I did not play around with it very long, but I do know folks use it successfully.
It has great mass to it.

I decided to go for casting gray iron, and I was clueless for a long time about how to melt and pour that correctly.

Gray iron is just so very nice to work with.
Takes a lot more heat to get to pour temperature, but well worth the time and trouble in my opinion.

.

 

[user 50514]

Hello guys,
I don't cast, so no knowledge to share on that. But I do 3d print, a lot! My printer hardly stops.
So from the surface of the model point of view I would always expect to have to rework some features. I know with casting you do have to face and bore or drill holes afterwards, so these are not an issue. But surface features on the 3d print can be a lot more then just layer lines. Depending on the quality of your printer you could have edge bulging, ringing or ghosting, strings and then the layer lines. Also when you have overhang, supports or a bridge, all these need work afterwards.
If the parts are small and intricate, You could reduce these by using a smaller nozzle, which will increase print times. But you can also lower the print speeds, which will also slow the printer down obviously.
I found when I am printing PLA with very fine details, I can get away with most layer lines with a nozzle of 0.25mm(, but I have ordered a 0.15mm now), and speeds of well below the default given of 60 or 50 mm/s(machine depending). The enclosed photos show a valve head printed with a 0.4mm nozzle and 0.16mm layer height, while the piston rod is printed with a 0.25mm nozzle and 0.10mm layer height. Those 0.06mm layer height is a huge difference and I am hoping to get even smoother with the 0.15mm later.
But as always you will get some finishing work to do on the surfaces like hairs or a seam line.
To give a sense of scale in my photos, the valve head is 0.25" high and that rod is slightly over 1" between the centers. Both were printed upright, so the layer lines on the rod are sideways, not the more visible "ringing" you can see just below the recess.
Also the valve head printed in 7 minutes each, while the rod and cap printed in 2 hours per set. With 3d printing you need to be patient.

 

[Bazzer]

There are PLA varieties made specifically for lost PLA casting. They have low ash and burn out more easily. I have heard that some are very soft and don’t make good prints. Good reports on others. Check this out on Amazon:

Polymaker PolyCast Filament 1.75mm for Investment Casting 750g Cardboard Spool - 3D Printer Filament for Lost Wax Investment Casting, Similar to Wax Filament for Metal Casting Plaster Cleanly Burn Out https://a.co/d/5J3QGSH

With Polycast they chemically polish the lines out, melting the surface would be another way to describe it.

My tests with Polycast prints seem to confirm this, now to shelling the parts and casting.

 

[Bazzer]

There are PLA varieties made specifically for lost PLA casting. They have low ash and burn out more easily. I have heard that some are very soft and don’t make good prints. Good reports on others. Check this out on Amazon:

Polymaker PolyCast Filament 1.75mm for Investment Casting 750g Cardboard Spool - 3D Printer Filament for Lost Wax Investment Casting, Similar to Wax Filament for Metal Casting Plaster Cleanly Burn Out https://a.co/d/5J3QGSH

With Polycast they chemically polish the lines out, melting the surface would be another way to describe it.

My tests with Polycast prints seem to confirm this, now to shelling the parts and casting.