This is my first try using ceramic shell. I decided to use a part I had printed that I knew would not come out well using the block casting method. I was curious to see if it would have the same problems as I would have expected from the block casting process. There was a bit of a learning curve for me as I seriously miss judged the weight the shell would take on. Im just going to chock this secession as an learning experience..... I have a couple more parts to try out that Im currently building the shell up on and will cast up in the next couple days. Stay tuned...
LOTS of good learning going on here David. Here's what I see. 1st I think it looks really promising! The text, the wax wasn't necessary at all. Notice you have one tiny hole up on the far right, that wasnt filled with wax and looks perfect. So we know the very first slurry coat made it in there. I noticed you didn't use a brush on your first dip. That "print" coat of slurry is really important and I would even be tempted to thin some slurry with a tiny bit of water in a separate container and paint brush the first layer on. Then I would let it dry for a few hours. Then the next coat, dip in the bucket, paint with a brush, and hit it with the fine silica. Again, let dry for a few hours. Repeat another slurry/fine layer, let dry. Then rock your umpteen layers of dip and coarse silica. You see that investment picks up EVERYTHING, nice detail on the print lines. lol I know you didn't print that thing, but cutting back on the fill will help. I wasn't really in love with your narrow entry point. I'm sure that PLA when it burns out must give off some gasses as it doesn't turn to liquid and drip out. A means to get that gas out could help your shell from not cracking. Just like printing supports, some additional and removable things sticking off the part can help with this. It's the same way some guys solve the cracking problem with wax and patch later after burnout. The interior of the shell cracking away from it's layers occured, leaving those boogers under the text on that corner. Why that happened and in that spot is still a mystery to me. I'm not a shell expert, but the grip of the shell onto the pla in that spot was seriously aggressive. When the PLA cooked in that spot, it for some reason, binded to that first layer tenaciously and came off during burnout. Hmmmm.. Need a good think on this.
Jason, one thing to keep in mind it that pla plastic is very hard and when it is heated it expands and puts alot of stress on the mold. Most of the fails i am seeing on the shell casting are the same defects i would have expected to see doing it as a block casting. Blind holes, lack of fillets and small text are always troublesome. Venting to releave gas pressure is a very valid point, one that i will have to think about in the future. For now i just wanted to see if the shell casting could over come the biggest plague of lost pla casting, blind holes... Ill have to see if i can find the cad file for this part, then try it again maybe using some different materials....
I never would have thought this stuff would expand. Collapse onto itself under heat, sure. But that would explain why R&R said 10 layers! If you print it thin, maybe it will expand into itself as the hardening shell holds back the pressure of expansion...? Solving a new mystery is always fun. Documenting it is important for the next guy. (which could be me) I no longer have access to fancy CNC machines, printers and fricken laser beams. But might walk the road myself in the future. For now, I'm making myself go old school as I master the fundamentals of this liquid metal thing. I do know, I am a fan of this ceramic shell and getting it dialed in with 3d printing will be the cats meow. Funny how it always comes back to the original artwork and less about the 10seconds dumping a pot of metal. I'd like to see a simple basic cube printed a few times with different degrees of fill, shelled, burned out and cast. Might shed some light on this. (walk before run thing.... )
Dont think a cube would be a problem. Its blind holes that is the problem, or the materials depending on how you look at it Ive been playing with this for a few years now, still waiting on that perfect printing material. Some filaments i have used can eliminate the problem, or drastically reduce it. But they have thier own quirks where they dont print as well or burn out cleanly.
Ive played with the cx5 in block form. Interesting stuff. Best for casting is the printable wax from machinable wax , but it can be finicky to print with. Best for smaller stuff that doesnt require alot of bridging or retractions. Prints that can be done "spiral vase" are pretty easy with it though. Then comes moldlay, good stuff but bites me in the ass sometimes on certain prints. Going to reprint the part in the video with it and see if it gets me there. Abs works ok, but leaves residue in the mold, not to mention stinks up the whole neighborhood when you burn it out. Plain old pla prints like a champ, burns out clean, no stink, but has a downfall with blind holes. Plan on trying petg , it prints well and seems to burn clean. Further research needed. Need to order some more machinable wax as well, someone said they redid their formula and its easier to print with now, plus i have direct drive printers now where before i was running it thru a bowden tube. Thats bound to make life easier.. Wood fill filaments like colorfabb has print great, but are horrible for casting due to the ash.... hmm but you know what. The ceramic shell can be cooled, blown out, and reheated where the block castings could not due to cracking... Yep, im thinking out loud again...
https://store.adambeaneindustries.com/products/cx5-sculptable-filament https://www.kickstarter.com/projects/adambeaneindustries/cx5-sculptable-filament-for-3d-printers Still waiting........... :-/ Photo is linked from their website. I wonder if the linked photo default size can be manipulated?
I didn't give them a dime. I'm not a real fan of publicly begging for money. Many of those are straight up scams. AvE just did a video about a laser printer that is a joke. The Cx5 filament is probably the answer if it burns out like wax. I bet bean industries didn't even think about what you are doing with lost pla.
Their filament is geared to the sculptor, not the metal caster. Judging by the high solids content I doubet it would be of much use for metal casting, unless you can get it all out of the mold before firing...
I gather the selection of that part is more about it being a candidate to test whether or not shell handles the blind holes any better than block. As an aside, for small qty or low volume production blind holes that need to be machined anyway are rarely worth tooling into the casting. I know the design manuals bang on about uniform wall and hot sections but that part would have them anyway and the difference in mass is about a zero factor to what a well-placed bob or riser would do. Besides defects and yield, many times it is unhelpful for machining because casting machine fixtures and fixturing castings are imprecise and it makes using drills for the ports more difficult because you’re often faced with more stock on one side of the of the as cast hole than the other and drills don’t respond particularly well to that. If they’re being machined by CNC with an end mill, enough said, but still not worth tooling them in and may as well engrave that logo CNC too. If you want the logo net shape, emboss it. For the blind cavities in the webbing, you’re stuck. For a high volume, hard tooled, permanent mold or die cast part, I’d say all the traditional design guide rules apply and tool everything in. You mentioned in the video that the part had blind holes and was cored. How is it cored other than the blind holes? WRT to intended purpose of your test, working the slurry after dipping with a small paint brush in the blind holes may help as well as more turning/spinning of the part as you did post dipping so the slurry doesn’t puddle in the holes and has more uniform coating thickness compared to the rest of the part. The use of a surfactant on the PLA may also help everything lay down better and provide a little better structural integrity to the shell in the problem areas. Obviously you can print XPS but if that part was an XPS foam pattern, I bet it would cast as is coated in drywall mud. I think the part is similar in nature to my finned cylinder head experiment. I used highly thinned mud and after dipping/pouring worked it into the fin roots with a small paint brush. The root of the fins were initially full of voids and air pockets. The other reason I’ve come to like mud as a foam coating is how well it lays down and covers the foam on the first coat. That XPS is very hydrophobic and most other (water based) coatings tended to puddle, and produce patchy coverage, even more so on wax features and I suspect PLA may have similar issues. I also think I could get that logo to cast as is but would work the mud in several coats by tracing through the logo with a tooth pick. One thing about lost foam is you don’t have to deal with the pattern expansion, and I suspect even if you cook it out of shell, it can’t exert as high of forces as more dense pattern materials. Another thing I noticed in the video was despite the recommendations to preheat the shell 300-500F after firing and prior to pouring aluminum, the surface finish and part otherwise appeared just fine from a room temperature pour. The pour also looked very tranquil. It just filled right up like you were pouring a drink. Looking forward to the next goes. I received my Suspendslurry this week. Best, Kelly
Yes this was just a test to see how the shell handled blind holes and to get an idea of how the slurry works. I have been sitting here looking at the part, and I know some of the defects were caused by my application of the slurry. I didnt let it drain long enough, or dry enough in the cavities before applying the next layer. The part has internal cored passageways for the oil to flow thru it. the shell must not have been getting good and dry in those areas before applying the next layer and when I poured the aluminum it managed to run into the middle of the shell in those areas filling in any voids it could find. Probably a crappy explanation but think of trying to cast a tube, then winding up with a tube that has a rod in its center that is attached to the inside of the tube in spots. Another thing I noticed in the video was despite the recommendations to preheat the shell 300-500F after firing and prior to pouring aluminum, the surface finish and part otherwise appeared just fine from a room temperature pour. The pour also looked very tranquil. It just filled right up like you were pouring a drink. There is no doubt in my mind that casting into lower temp molds produces a much better surface finish. This is highly apparent when block casting aluminum parts. the way aluminum will cool in a block mold can defy the laws of gravity because of the way it cools in the mold. If you were to cast two balls exactly the same size with one positioned in the center of the flask and the other 4" above it to the outside of the flask the higher ball will draw metal up from the lower one as it cools first. Also if the mold temp is high an aluminum part can develop a crystalline pattern on the outside of the casting as it cools. As for part design, people send me stuff that hey design for me to cast. What they usually send is a cad file of the finished product and not a cad model of a casting. This can make things very challenging as STL files are not easily modified. If I had an IGS file of this part I would cnc it out of xps foam in sections, glue it together and cast it that way. Maybe? could also do it in wax.. Im going to see if i can find that model file...I want another crack at it with the knowledge I have gained from this attempt....
OIC now. I think the humidity in the confined space dramatically slows down the drying. When I applied coatings to the inside of those tubular parts they literally took days to dry when the exterior coated at the same time took 1 hr and they were 7/8" ID with three openings. When they were outside perched above a warm surface in the sunshine and breeze, much better. But when I didn't have the sunshine or want to leave them outside, I put them under a 5 gal bucket spaced 1/4" off the ground with a 100w light bulb and pointed a little trickle of compressed air at the tube opening and they dried right out at about the same rate as the exterior. The light bulb typically produced 150F or better under the bucket. A little heat helps vapor pressure a bunch. Good luck getting the shell out of the interior. Game on! Best, Kelly
