Lost PLA processes, products, knowledge.

[Jack3M]

I need much more knowledge about this before I start purchasing the 'lost' products and what I need to purchase. Research on this site reveals some content, not enough. and hopefully this can be beneficial to others as the thread progresses.

My only attempt was last year and I used plaster of paris, let it cure, and fired it in my forge. Well a few spots survived, which was enough to get the idea of just how good the castings would be. But plaster of paris is not the product to use as it just crumbled to almost nothing during the firing.

Which investment is suitable for this and will survive the firing?

How do you assure all the ash from the burned out PLA is removed from the mold?

Do you vent the mold?

Does the mold need anything to keep it from breaking before you are ready to remove the casting?

What do I need to ask that I don't know? My experience is limited to sand casting with aluminum, brass, and bronze.

 

[Richard Carlstedt]

Jack, I am in the exact same boat as you as far as seeking knowledge for PLA use.
I do have experience in lost wax and will say you need to use investment as a casting material.
Plaster can work, but is much weaker. When you heat investment to 1300 degrees, it changes its structure to almost a ceramic (IMHO) material and is stronger .
Try a name here
http://woodsmere.com/AppendixF.pdf
I use Kingsley in Michigan and also Riogrande
https://www.riogrande.com/
For very difficult parts with aluminum patterns,(which might help you) I have done 2 piece molds like sand casting, but using investment
Rich

 

[Richard Carlstedt]

Oh yes, I use a product called "Satin Cast" and always use a steel container for holding the mold
Steel "tin" cans are great with both ends removed from small cans to big coffee cans
Investment needs the support during heating process
Normally they use stainless steel tubes like 2 1/2 diam x 5 inches , but cans are cheap

Rich

 

[Jack3M]

Have spent hours and hours watching utubes of anything to do with lost process casting. (multiple different materials) Frequently folks are using POP (plaster of paris) with silica sand in multi layers and using the sand also in the main casting pour....in POP. Very little information on what is left after burnout of PLA. One industrial site said nothing left but still blew out the mold.

 

[Richard Carlstedt]

Right , very little info, and that has slowed my venture into 3D printing
A friend is going to make a part for me and I will determine if the lost wax performance is worth
buying a 3 D printer . I know this Jack, you need to reach 1300 F with investment as I had molds blow up when heated to only 1150 . In a controlled experiment I got water coming from a 1100 degre burnout m so the investment ( and POP) change structure, even though the mold was preheated to 350 for 3 days (!) . It isn't wax you burn out , it's the chemical conversion...the books are nuts ( wrong) and say wax burnout. I had them blow with no wax at all so the term burnout is bogus.
Rich

 

[bmac2]

 

[Raviv]

i have a lot of experience with 3d printing lost wax procedure, i have tried many materials and came up with a process that is rather easy to do with some home tools.
i am currently designing my own spin of a radial engine and casting some of the parts.
designing the parts in a CAD software, printing them on my Ultimaker-3, going through an investment casting process (a list of material and procedure will follow), i manage to produce highly complex parts, with many curves and details (cooling fins, for example, which is rather difficult).
i tried PLA as "lost PLA" and found this process to be difficult, as it needs a very high burn temperatures, which eventually crack the plaster of paris mold.
i tried "machinabe wax" filament, found it to be very difficult to print, as it wont adhere to the print bed, will suffer from layer separation and deformation.
the best material i found to be working fantastically is "moldlay", parts are printed almost hollow (very low, if ever, infill), then i use a thin mix of plaster of paris/sand/water to spread the first layer with a painting brush, repeat the process for approx 5 layers, building up the mold.
then, the easiest thin to do - put it into the kitchen oven for 1 hour at 120c to dry it out, then at 270c for approx 2 hours, the moldlay will run out of the mold like wax, and what that is left will burn out without any residue.
usually pouring the aluminum into a hot mold, which helps with the final part's details.
my prats are no "designed to cast", which means that i design and print them with the pouring spout, spur and riser, all of these are been covered with plaster of paris to generate a mold.
when i design the parts, i always leave enough room/material for machining.

 

[Raviv]

a few pics , hope you will find this informative
printing the parts using Moldlay

after approx 5 coats of plaster of paris, heating up in the kitchen oven, as you can see, it is clean without any residue

casting

this is how the parts comes out of the mold, the left one was cooled too soon, this is why the surface looks a bit dull

the parts, comparing to the PLA model of them, after some machining.

 

[Jack3M]

Researching Moldlay was informative. Expensive. Very expensive. But.... Worth a try, will order some.

 

[Raviv]

the main problem i came across is that Moldlay doesnt have too much information available of the web, and their example is just horrible (the broken mold part).
maybe i will give lost PLA another chance, but as for now, the ability to "burn" the part in my kitchen oven and maintaining very good details, is just priceless.
i am improving the method as i go, learning from mistakes and issues i came across with, but i did manage to produce some very nice casts with all the internal passages.

just one thing to remember, which i cant stress enough - design your parts for casting, with the needed overhead for machining, mold venting, and overall castability.
what are you planing on printing and casting ?

 

[Jack3M]

Parts for steam engines. I have already learned to give myself material to machine. What temp do you find it prints best at? With or without the heated bed? The plain oven burnout is enticing.

 

[Raviv]

i print moldlay at 185c with the bed heated to 55c-60c, it sticks to the bed very well with no deformation , although i always print with 5mm brim for better bed adhesion.
the first time i took the mold out of the oven, beside the smoke (vent your kitchen, send the wife to visit a friend ) i was very excited, that was after a few failed attempts with PLA, and a lot of residue from machinable wax.

 

[Jack3M]

Well is ordered now need some investment which I can get locally Got some figurine figures I got off the net to try this stuff out. Going to go collect my scrap aluminum and melt down to ingots while I wait.

 

[kadora]

Hello guys
I am looking for cheap casting process because electricity bill for firing investment at 1300 C would ruin me.
I use practically the same process like RAVIV but for lost wax casting.
I think that good mould must breath out hot gases this is why I cover wax pattern with tiny layer of plaster only
// like eggshell//.
Only tricky part of this work is to cover wax pattern with plaster //plaster refuses to stick on wax surface//.
When plaster layer // 1-3 mm thick// is hard I bury it in sand and in oven at 120C I remove wax from mould.
Then 2 hours in oven at 350C and finally pouring aluminium into the hot mould.
My results - from 5 AL pouring one casting is good and four castings are bad see pictures .
I have tried to use a meltable soap instead of wax but plaster does not dry on the soap surface.
I hope this can help .

 

[vederstein]

If you're doing one offs, why not lost foam?

I bit less than a year ago, my experiments with lost PLA were a disastrous failure. Lost foam worked, but I eventually finalized with sand casting.

This may sound stupid, but I know that some people have converted their 3D printers to print chocolate. Now that's a material that's sure to melt out.

...Ved.

 

[kadora]

Chocolate pattern ? ? ? not so stupid idea.
Foam is porous material , I think , by using this is not possible to cast smooth surface.
Maybe Im wrong.

 

[Raviv]

if you have a 3d printer, the entire concept of "lost foam" is obsolete, since you can design your part using a CAD sw, print it and cast it...
not sure how you are going to make a foam part such as a cylinder head or any other complex parts.
moldlay works perfect for me, i can "burn" it in my kitchen oven and get a clean and dry mold to pour the aluminum in it.
i tied it with PLA, no luck.
if anyone else have any other idea about how to make a pattern that will be easy to melt without any residue, please share it.
chocolate pattern sounds nice, but i will probably give it a bite before casting it

 

[arvidj]

Disclaimer: Have never used either ...

While looking up Moldlay I ran across PolyCast ... https://www.amazon.com/dp/B07J678V8C/?tag=skimlinks_replacement-20 ... No experience or affiliation with either product or company. Just wanted to add to the information ... or misinformation as the case may be ... base.

 

[editor123]

I talked to the Print2Cast suppliers. They told me that using Gaffer or Athletic tape would allow the wax to adhere to the build plate. That does work well. I placed Gaffer tape on a glass plate and clamped that to my heated build surface. The wax almost sticks too well but with a raft between the tape and the model, it works OK.
What I did find is that the feed path for the wax filament needs to be of low friction and as short as possible. So I am mounting the reel directly over the printer and no using a feed tube.

 

[abby]

There are two types of investment casting namely block mould and ceramic shell.
ceramic shell enables the casting of steel and is probably the most common commercial process.
Block moulding is plaster based and allows casting up to 1200°C although there are specialist products which can handle platinum casting.
Block moulding allows for vacuum assistance and makes the production of hollow castings easier then ceramic shell.
There is talk here about melting the pattern so that it runs out of the mould , all of the molten pattern cannot be removed in this way.
Some will be trapped inside the mould.
It is necessary to burn out the residue at 725°c for plaster based investment.
Wax for lost wax casting has zero residue providing that sufficient oxygen (in the form of air) is available during burn-out.
Straight Plaster of Paris is unreliable as investment material , it will expand and crack during melt/burn-out.
This is not to say that it will never work but the time and expense committed to the patterns ,whether in wax or a suitable printed plastic , is in my opinion not worth the risk just to save a couple of quid (bucks)
Commercial investments are a mix of refractory such as crystobalite and plaster such as herculite to give a strong and reliable product.
The plaster component contains water of crystallisation which will only be driven off at 550°C.
Another factor to consider when casting aluminium is the strength of the investment.
During cooling and freezing the aluminium has less strength than the investment so hollow castings are prone to contraction cracking.
The advent of 3D cad , home printing and pattern printing media suitable for sucessful burn-out have put the investment casting process into the hands of almost any home workshop user.
The above are just a few points that need to be considered for reliable casting results and of course for safety sake , residual moisture and pattern material can cause molten metal to be ejected with great force.
Once you have mastered the process there is almost no limit to what you can make.