Back at it. Lost pla cast iron ceramic shell

[Harry.]

Sorry but I do not, some of my prints are 40 hours long...

I went to the TCT 3Sixty show about 3D printing and I'm looking into getting a 3D printer that I can use at home. I'd like to try the lost PLA method and my brother has a home furnace that I can use. At the show, I got the impression that 3D printing is becoming quicker and more popular, its even used for medical implants according to this website: https://www.machinedesign.com/search/node/future of 3D printing

 

[Harry.]

Yes I have considered it...along with everything else! I'm reading and watching a lot now. I still don't get how the cavity is able to fill without and air pockets with the ceramic shell method, but in many videos it does not seem to be a problem.

Can you recommend a youtube channel about 3D printing castings and lost PLA method?

 

[pjpickard]

https://www.youtube.com/channel/UCkEYj8wtK3aEW8vSGhlB43g

and

https://www.youtube.com/channel/UCNC9gjgYrzLfyMQmp31DnjA

 

[Harry.]

Thank you so much those channels contain lots of interesting ideas. The first one that came up was a planetary gearbox, I'd love to try it to see how my casting compares to a precision machined version.

 

[ddmckee54]

aonemarine:

40 hour prints? I sweat bullets over 20 hour prints, what were you printing and how big was it?

Details please, layer height, infill %, wall thickness... inquiring minds want to know.

Don

 

[aonemarine]

aonemarine:

40 hour prints? I sweat bullets over 20 hour prints, what were you printing and how big was it?

Details please, layer height, infill %, wall thickness... inquiring minds want to know.

Don

Lol it was a flat head engine model. .1mm layer height, .4mm nozzle, no supports, and mostly a single wall. It had to be printed very slowly to get it to come out.
Also printed a t rex skull that was scaled to maximum size on my rostock. .1mm layers 2 shells 20% infill .4mm nozzle.
There's been other prints. Those two are the ones burned in my memory.
I tend to slow my prints down speed wise to get better print quality and seem to have less issues with nozzle clogs when I do. Nothing worse than being 39 hours into a 40 hour print and getting a jam.
Only so fast you can melt the pla, and cool it before the next layer...Abs is a different story.
I know some people print at blazing fast speeds, I'm just not one of them..

 

[ddmckee54]

What do you consider a blazing fast speed?

I typically print at 60mm/sec, I can push it faster, but as you say, the print quality goes down. Now I'm mostly printing what are structural parts for a CNC router that's loosely based on the MPCNC. I use a 0.4mm nozzle, a 0.25mm layer height, 4 perimeters, and a 40% infill. The infill is probably overkill but in most cases I want the structural rigidity. So far I'm sticking with PLA, my printer is in my living room and I don't mind the smell of the PLA as the printer works.

Don

 

[awake]

I use a 0.4mm nozzle, a 0.25mm layer height, 4 perimeters, and a 40% infill. The infill is probably overkill but in most cases I want the structural rigidity.

Don, some of the 3d printing gurus that I follow have been saying that increasing the infill makes less difference than increasing the perimeters - IOW, you might be further ahead to use, say, 6 perimeters and 20% infill. Since I have read this, I have not needed anything overly strong, so haven't experimented with it myself. I have, however, experimented with different infill patterns. One that I find very economical to use is a 3d hex - 20% with that pattern seems to be equivalent to 30% with some of the others.

I'm certainly not an expert, so take anything I say with a grain or two of salt!

 

[Shopgeezer]

https://www.youtube.com/channel/UCkEYj8wtK3aEW8vSGhlB43g

and

https://www.youtube.com/channel/UCNC9gjgYrzLfyMQmp31DnjA

Rats. The first video on casting with PLA prints shows mixing and pouring the investment and then jumps to pouring aluminum. Nothing about how he burns out the PLA. That is the part I want to know more about. Temperatures, times, problems with residual plastic in the mould and so on. His prints look too perfect, more like resin printing.

 

[awake]

Shopgeezer, which you-tuber are you referring to? If Myfordboy, keep watching - he does some where he shows burning out the PLA. As best I can tell, he set the mold where the PLA can run out, then heats it in a controlled oven. So, more of a melt-out than a burn-out.

 

[Shopgeezer]

The first video in the quote in my message. The guy makes a planetary gear box. Pretty cool little project. All the steps are there except burning/melting out the PLA. But in my reading and You Tubing I have seen various opinions on this. Given that I print around 200C (392F) a kitchen oven at 500 F should melt PLA out of a mould. But is this sufficient? Would there be residue left in the mold? Do you have to use a kiln and actually burn out the PLA?

I am looking into a filament called Moldlay that is intended for lost wax casting and apparently easy to melt out. Its hard to find. Also seems to be challenging to get good detail in the print.

 

[aonemarine]

The first video in the quote in my message. The guy makes a planetary gear box. Pretty cool little project. All the steps are there except burning/melting out the PLA. But in my reading and You Tubing I have seen various opinions on this. Given that I print around 200C (392F) a kitchen oven at 500 F should melt PLA out of a mould. But is this sufficient? Would there be residue left in the mold? Do you have to use a kiln and actually burn out the PLA?

I am looking into a filament called Moldlay that is intended for lost wax casting and apparently easy to melt out. Its hard to find. Also seems to be challenging to get good detail in the print.

The time it takes to properly burn out the mold is dependent upon the size of the mold. A larger mold will take longer and require more stages of heating than a smaller one.
If you go to the ransome and randolph website you can pull up the tech sheet for the plasticast investment and get the burn out times and temperatures for various size molds.
When it comes right down to it, you are not burning out the plastic you are burning out the investment. You need to be able to get the mold to 730C and hold it there to properly calcify the investment. Although people have managed to burn out pla prints at lower temperatures I would not recommend it. The pla will burn out perfectly clean with no ash left behind. Lost plastic casting is nothing new (although many think they have reinvented the wheel) its been around for over 20 years. A quick check of the patent date for the plasticast investment shows this....Hope this helps...

 

[aonemarine]

https://docs.wixstatic.com/ugd/cc5f22_306ba9f48fa940269dbe7e4a7156ef35.pdf

 

[Shopgeezer]

The Ransome and Randolph info is enlightening. Interesting point about setting the plaster at 370C and removing the pattern at 730C. The Moldlay filament will liquify at 280C so the thermal transition temp of 370C should do both jobs. Not clear from the info if raising the temp to 730C is necessary for the plaster to cure or just recommended to remove a plastic pattern.

 

[aonemarine]

The Ransome and Randolph info is enlightening. Interesting point about setting the plaster at 370C and removing the pattern at 730C. The Moldlay filament will liquify at 280C so the thermal transition temp of 370C should do both jobs. Not clear from the info if raising the temp to 730C is necessary for the plaster to cure or just recommended to remove a plastic pattern.

Dont reinvent the wheel. moldlay may melt out at 280c but it what temp does it need to reach to completely burn out any plastic that becomes entrapped??

 

[Shopgeezer]

Not sure what temp the Moldlay would need for burn out. I guess that is a question for the manufacturer. The filament is supposed to be much easier to remove than PLA. Does that mean a complete burnout at a lower temp? Even with a bit of filament pooling in some parts of the mould, would the molten aluminum vaporize it? Some research required.

 

[aonemarine]

Not sure what temp the Moldlay would need for burn out. I guess that is a question for the manufacturer. The filament is supposed to be much easier to remove than PLA. Does that mean a complete burnout at a lower temp? Even with a bit of filament pooling in some parts of the mould, would the molten aluminum vaporize it? Some research required.

I've tried lower temp burn outs. Things did not come out so well and the aluminum was not able to fully burn out the remainder of the pla which showed up in the casting looking like bits of carbon..

 

[dazz]

Hi
I have never cast any metal but my research indicates that the burnout environment is important. Oxygen is required to convert the carbon to CO2 rather than just leave a carbon deposit. This points to an electric kiln, with drainage, being a much better choice for burn out than a fuel fired furnace.

I want to cast iron so I am looking at getting both an electric kiln and a fuel fired furnace.

Dazz

 

[mnay]

What brand or type of investment do you use?
I see a lot on Amazon but they don't give what temperature they are good for. I will be casting aluminum
thanks. I have learned a lot from your posts.
Mike

 

[aonemarine]

What brand or type of investment do you use?
I see a lot on Amazon but they don't give what temperature they are good for. I will be casting aluminum
thanks. I have learned a lot from your posts.
Mike

For lost wax I use the Ultravest, and for lost pla I use the plasticast. Both are made by Ransome and randolph. I think someone also makes an investment specifically for aluminum casting (if your not using vacuum assist) that is more porous. I just cant remember who right now....