Question about lost PLA casting

[Shopgeezer]

Having 3D printed for years I am curious about resin printers. I have seen amazing quality in very complex prints. It seems gamers use them for creating figurines and many of these are incredibly complex. It would seem ideal for small engine parts and I have seen resins advertised for casting. I think jewellers are using this tyoe of printer.

I know little about resin printing but one thing that bothers me is the extensive use of supports. Parts don’t seem to be printed flat against the platen, they are held at an angle with a forest of supports. These supports would leave a lot of scars and must take a long time to clean up. I don’t understand the need to print like this. Anybody out there doing resin prints for casting?

 

[GreenTwin]

I thought resin printers would be the wave of the future, but after reading about them, I am not so sure.

The resin apparently has a shelf life, has some serious vapor issues, and the print needs to be fixed? in a second solution/wash.

Resin prints may be good for special applications, but for day-in day-out pattern printing, I think PLA is hard to beat.

That is just my observations.

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[user 50514]

It is horses for courses. Resin is hard to beat on minute details and smooth surfaces. But the process is nasty, dirty and smells. Besides the waste materials you need to comply with local laws for disposal, I think even if you were allowed, to simply flush it down the loo is criminal.
I would never have resin printing as a hobby at home, but if I needed it for something, I would put it in my work place.
Another big advantage of resin printing is that the print time is not increasing when you fill your build plate with copies. If you need 20 or 30 copies of one item, resin beats fdm hands down on time.

 

[Shopgeezer]

I think resin prints need to be fixed with UV light. There are UV chambers with a turntable you can buy or make your own. Leave in sunlight? It seems to be a good process for small detailed prints but most of my printing is large objects and this is not possible with resin. Small engine parts for casting would certainly be possible. FDM prints don’t work well at tiny scales but resin prints do. We all need both types of printers. I’ll inform the wife.

 

[lee webster]

I use a resin printer for pieces that need fine detail, and an fdm printer for pieces that need strength. A piece can be printed on the print bed, but that might make it very difficult to remove after printing. The first several layers of a print are exposed to uv light for about 40 seconds or so. This is to "bake" these layers onto the build plate to make it more secure, you dont want a print to come loose! I raise my prints off the build plate in the slicer programme by at least 5mm before creating the supports. I will then use the software to remove or move any supports that I feel are not in the right place, and add more supports if I think they are needed. Better to have more supports than less. The surface of the printed part that is closest to the build plate will have most of the supports on it. This can make the surface uneven as the resin is trying to bridge the gap between the supports, a bit like a hammock sagging in the middle. I recently resin printed the bonnet for a 1/10th scale vintage car. The bonnet has 120 louvres in it, and because it was supported from underneath, the louvres were perfect. The louvres measure 6mm wide by 3/4mm high. There is no way I could do that with fdm. The body of the car is fdm printed and is too big for my resin printer and it would also have been too fragile.
I use only water washable resin, and dispose of the used water by leaving it for several days in a plastic bottle to settle before pouring it on a piece of rough ground in my garden. (If there is better way please tell me) It doesn't seem to harm the plants. I use isopropyl alchohol to wipe the print afterwards. The resin has very little smell and can't be smelt 10 feet away. The ipa is smellier but very little is used, I also use the ipa to clean the resin tray after washing it out with water.

 

[100model]

Mu patterns

Forgive my ignorance, what does Mu mean?

 

[user 50514]

Forgive my ignorance, what does Mu mean?

I think he meant My, but in technical terms in metric, it could be short for micron, from the greek letter Mu (not on my keyboard so I cannot show it here ).

 

[GreenTwin]

Forgive my ignorance, what does Mu mean?

That is the British pronuciation of "my". LOL

Modeling humor.

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[werowance]

folks i really do appreciate all the wonderful in put. here are some of my challenges.
1. i only have a xyz Davinci Jr. 1.0 printer. i have to use their fillament as it has a chip or rfid tag on it
2. i just plain suck at making sand moulds. i have trouble doing just simple half/half moulds much less a 3 part or more mould.
3. i do have access to multiple kilns so i can do the burn out that way and ramp up slowly.
4. i have painted wax on with a brush but sometimes i have had it warp the part due to heat. maybe wont be an issue here.

please keep on discussing as i am picking up a wealth of knowledge but i did want to chime in and point out my challenges on this one.

thanks very much for all the input. keep it coming

 

[creast]

folks i really do appreciate all the wonderful in put. here are some of my challenges.
1. i only have a xyz Davinci Jr. 1.0 printer. i have to use their fillament as it has a chip or rfid tag on it
2. i just plain suck at making sand moulds. i have trouble doing just simple half/half moulds much less a 3 part or more mould.
3. i do have access to multiple kilns so i can do the burn out that way and ramp up slowly.
4. i have painted wax on with a brush but sometimes i have had it warp the part due to heat. maybe wont be an issue here.

please keep on discussing as i am picking up a wealth of knowledge but i did want to chime in and point out my challenges on this one.

thanks very much for all the input. keep it coming

RFID chip? Not heard of that before on filament. I guess you could locate the chip/tag and put in on another brand of filament?
I have mentioned the following on another thread here but will repeat a bit of it.
My plaster moulds are made using a tubular flask ( 2" dia tube ) of stainless steel, just like jewellery methods, and use a rubber sprue base to mount the PLA model.
I use SRS Industrial A refractory plaster and when the flask is filled I vacuum it for about 4 minutes to reduce bubbles.
The mould is left overnight to set and then next day put through the burnout cycle with the mould upside down to allow molten PLA to pour out during the cycle.
My cycle is 0-180 degC over 30 mins and hold at 180 for 1 Hr, ramp to 350 deg C over 30 mins and hold again at 350 for 1 hr, finally again 30 min ramp to 500 deg C and hold for 1 hr. Allow to cool to approx 300 deg C for pouring or just let it cool slowly to cast at a later time (needs to be slowly heated to 300 deg C if done from cold)
Manufacturers specify even longer/higher temp burnouts but I have had great success on my rushed cycle (impatient or what?)
The casting needs to have vacuum assistance to ensure good fill. I have knocked up a cheap Chinese vacuum pump (£15) to a plate with a silicone seal to do this.
I intend to revamp my vacuum assist for using perforated casting flasks as this gives a more reliable fill. Vacuum is essential to the filling of the melt.
Attached are pics of my latest Brass casting, its about 30mm diameter. You can see how the layer lines are very prominent but I find sanding Brass easier than PLA!

 

[GreenTwin]

I have seen folks make lost PLA castings, but have not done them myself.

I have tried a lot of other methods and materials, such as Petrobond, greensand, resin-bound sand, and sodium silicate bound sand.

I would recommend experimenting with small items, and see if you can find a combination that gives you good results.

It took some experiementation on my part to find the right combination of materials.

For resin-bound molds, I spray on an alcohol-based ceramic slurry, and this works well with iron, and gives a clean finish with no burn-on right out of the mold.

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[werowance]

been experimenting a little. found that plain white elmers glue works well to smoothe the lines out. i just used a little water color paint brush to apply it thinly. seems to burn off easily as well. i tried it on 3 little test parts. on melting the pla i tried those 3 piecs in the bbq grill and at around 500F the pla was smoking and running but as another in this post said would not be hot enough to burn out. the round part on the right of the photo is what i want to cast in aluminum at first. the large center is the sprue and there are then 4 vent tubes. the fluted part in the bottom center of that is what i will call the actual part. i will use the late to part it off from that large sprue after i have done some slight machiing to the under side and such to it. - all this is assuming that i can actually cast it.
and on a totaly seperate note and i want to start out with i do know the dangers of zinc smoke and metal fever before i ask this. but if i wanted to make brass - say 260 brass or close there of. the porportions i assume are measured in volume not in weight correct? about 30 parts zinc to 70 parts copper right?

 

[GreenTwin]

I am assuming that it is by weight, but check me on that.

Here is some info on 260 brass.
Looks like it has trace iron and lead in it.
And it gives a comparison with 360 brass.


https://southaustinmetals.com/blog/a-guide-to-260-brass/
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[creast]

To be honest, from the size of that part you would be better off casting in sand. It looks a simple part but you are going to have shrinkage problems unless you make a massive feeder/riser.
70/30 Brass is the common ratio but making your own has it's own set of problems i.e you melt the copper and then add the zinc and woof!! up goes the zinc flare off which is pretty violent and you just don't know how much is actually in the alloy.
I have tried making bronzes but not Brass as it is so readily available in scrap plumbing fittings etc.
Indeed I am guilty of re-melting Brass multiple times and on occasion noted differing machining properties perhaps due to some contaminant from added scrap?
I always assumed that if the zinc was diminishing there would be a significant colour change of the Brass tending towards Copper but I haven't seen this.
On the Elmers glue side, I used to do fused glass and used that for arranging glass pieces prior to fusing and it does burn out clean but that was at 800 deg C .
Rich

 

[GreenTwin]

I have tried pouring brass in the past, as well as Naval Bronze.

I found it difficult to keep the zinc from burning off before I reached pour temperature.

A buddy of mine puts glass on top as a cover, but I don't want to deal with trying to get the glass back off the melt and off the crucible.

The art folks use Everdur, which is a silicon bronze, and does not contain zinc.
I have never heard of anyone having any significant problems with pouring Everdur.

If you want real brass though, then you have to deal with the zinc fumes and zinc burnoff.

https://atlasmetal.com/silicon-bronze-everdur.php
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[GreenTwin]

I also recall having gas issues (no pun intended) with brass.

Holding a metal at an elevated temperature often causes absorption of gasses, and I could clearly see small gas bubbles all through my brass casting.

I have seen brass degassing agent for sale.
Don't breath any fumes coming off of any degassing agents.

Edit:
One of the benefits of melting gray iron is that it does not seem to have gas absorption problems, for whatever reason.

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[creast]

Forgot to add.
When I pour Brass I don't get it so hot that it is smoking madly. If I skim the dross and get a nice green flare up then I cast.
Maybe this is pouring a little cool but 95% of my pours fill ok.
I have only ever had one casting with a gas issue or at least it may have been, Aluminium has been another matter!

 

[werowance]

covering in glass, now thats interesting. how did they do that? im imagining something like several scoops of just broken up glass jars or something thrown on top of the melt and then glass melts and makes a cover over the top? seems like borax does similar when i use it on aluminum which is also very messy on the crucible. but just for my own curiosity i would definately like to just hear more on that.

 

[creast]

Forget the glass. Maybe for Bronze alloys. But not required for Brass or Aluminium.

 

[creast]

Forget the Borax too. For Aluminium you can use drossing flux if you like.