Help me make another attempt at shell casting

Discussion in 'Investment casting Ceramic shell method' started by 01binary, Jul 2, 2018.

  1. 01binary

    01binary Copper

    Hello,

    I tried shell casting when I started working on my project but after 6 months of failures I decided to go with vacuum-assist casting (jewelry) method instead. This worked, but the last 7-10 parts of the project are too large to cast using this method, so I am going back to shell casting. I hope I could get more advice here to help me succeed this time.

    Here is the largest part I was able to cast with the jewelry process:

    Fig. 1: Wax positive for 2.7" x 12.4" x 0.7" part attached to a rubber base with sprues, and an extra-tall vacuum flask it will be invested in.

    [​IMG]

    Fig. 2: two mirrored parts cast in the same vacuum flask (one of them from the above wax positive) displayed with four copies of another part of the same assembly.

    [​IMG]

    Here are the wax positives for the larger parts that I can start building shells on immediately, because they are too large to cast with the jewelry process:

    Fig. 3: Two mirrored parts, each 6.5" x 9" x 2.5" bounding box.

    [​IMG]

    Fig. 4: One of two mirrored parts, 5.5" x 13" x 3"

    [​IMG]

    What went wrong last time:

    I had issues with cracking molds, which I finally solved by switching to Remet red pattern wax (above), only to find out that I couldn't get a polished as-cast surface with sub-millimeter detail on my shell casts. The main issue there was that the first layer of slurry failed to adhere to the wax, due to lots of extruded detail with sharp corners on the wax model.

    If I used more slurry to force it to cover the wax, it would crack like a desert floor and flake off when drying the very first layer. If I used less slurry, the first layer of flour would end up in contact with the parts of the surface that slurry would not adhere to, so I would get leopard-skin effect on the casting, where some parts were smooth and some parts looked like a sand-cast surface.

    In addition, many of the smoother parts still had a micro-foam like surface rather than perfectly smooth. I achieved a polished as-cast surface and sharp detail with the jewelry casting method, so I need to find a way to do the same with shell casting.

    Lastly, the slurry quickly lost its pH even through R&R said it was safe to use the bucket for dipping the parts directly. It changed color to become more yellow, all the sediment settled at the bottom, and then it started turning into foam with more bubbles each time I dipped. I could never get it back to original form, still not sure what I did wrong.

    Here's my research so far:

    Resources:
    Tips from machinemaker: http://www.alloyavenue.com/vb/archive/index.php/t-10459.html
    Shell building: https://docs.wixstatic.com/ugd/cc5f22_1b16abf7aa264790acb87e31d3ec63f0.pdf
    Slurry additives: https://docs.wixstatic.com/ugd/cc5f22_0102e9f605bc48ec903f00f2ed6431b7.pdf
    Slurry control: https://docs.wixstatic.com/ugd/cc5f22_c8b09a4fd433437a9137c10dd2619661.pdf
    SuspendaSlurry FAQ: https://docs.wixstatic.com/ugd/cc5f22_02c0e31fa28d476c920966b633772c32.pdf
    Howto videos: https://www.youtube.com/user/jagboy69

    Supplies: what should I get this time?

    1. SuspendaSlurry FS, 5 gallons

    Last time I used this as a back-up slurry, and SuspendaSlurry ZR as the primary slurry. I somehow let the salesman talk me into using ZR even through I was casting in Aluminum (non-ferrous), perhaps because I stressed the importance of fine details. This decision doubled the price of my materials and caused me to fail because it's harder to use. I think I would like to stay with SuspendaSlurry because I can only use my hobby space every other day, making constant mixing problematic. This differs from machinemaker's instructions (see Resources section above), as he recommends using Prime Coat with a fused silica flour - however SuspendaSlurry gained widespread use after he posted those instructions, so do you think I could succeed with it, or is it a bad idea?

    2. Wet-It wetting agent

    Recommended by R&R page at https://www.ransom-randolph.com/slurry-additives. Since my primary issue other than shell cracking was the failure of the first coat to adhere to sharp details in the wax model, this seems like a requirement for me to succeed this time. What do you think?

    3. Flour

    Last time I got Zircon sand for use as flour for the primary coat. If I am switching to SuspendaSlurry FS, should I get another flour? Perhaps I no longer need flour (and never needed in the first place)?

    4. Fused silica stucco (1 bag of "A": 50/100 grit)
    5. Fused silica stucco (1 bag of "B": 30/50 grit)

    I got these two bags of sand last time to use for the back-up coats. They are standard "A" and "B" presets from R&R, corresponding to medium and large grit. Should I get them again?

    Thank you for reading - I appreciate your time!
     
    Jason likes this.
  2. Jason

    Jason Silver Banner Member

    Welcome aboard brother in lost wax. R&R makes 2 different slurries. FS and ZR I think. One is for ferrous metals and the other for non ferrous. If you are pouring bronze, you will want the FS suspendaslurry. I'm pretty sure they will sell you all the crap you are willing to pay for. If you have extrememly fine details, you can always thin down the first coat of slurry with some distilled water and it will do the same thing as multiple slurries.

    I would be pissed at them if they sold me ZR if they KNEW I was pouring bronze. Glad I could help clear that one up for ya and save you a few bucks in the process.
    Please list your channel on the members with YT channels thread found here. http://forums.thehomefoundry.org/index.php?threads/members-with-youtube-channels.188/

    Those are some nice pieces there. I hope you share your process. :)
     
  3. Jason

    Jason Silver Banner Member

    Keep in mind, slurry HATES adhering to sharp corners. I have to ask, what is that wax and where'd ya get it. I'd like to find some specs and that might help identify your problem. There is something you can wash over the waxes to help with first coat of slurry adhesion, but I'll be damned if I can remember what it's called.
    PAGING ARTOSPY!!!!!!! (he's our resident shell expert in France, he's been busy moving so we may need a day to dig him up) Ya might try shooting him a PM and he will answer.)

    and no, skip that flour bullshit and see how it works out. Barry in Baton rouge at outback foundry and myself use nothing but the slurry and the 2 sized silicas
     
  4. DavidF

    DavidF Administrator Staff Member Banner Member

    you should be able to investment cast them in shall if you gate them to feed in at bottom and vent at top. just get about 6" of head over the casting and be sure to vent where necessary.

    Welcome to the forum 01, looks like you have been coming right along with the project since last I saw it...
     
  5. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    I'll be watching with interest.

    1. How were the master patterns made? 3D print with finishing?
    2. How were the waxes made? Silicone mold from master?
    3. What was the pour temp and mold temp for the aluminum?
    4. What are the parts for?

    Best,
    Kelly
     
  6. 01binary

    01binary Copper

    DavidF or anyone else: do you have a picture of a shell with vent at the top and feed at the bottom? I think I can visualize this, but I could be wrong. I imagine the vent at the top is just sprues coming together and feed at the bottom means... you still have the pouring cup at the top but route the sprues with a 90 degree bend to flow into the bottom?

    Jason: I will wait for a few days to see if Artopsy replies before ordering. My shipping is going to be around $300 so I better make sure I get everything I need. Thank you for the tip with slurry thickness vs. sharp edges. Just to summarize, I am planning to get:

    SuspendaSlurry FS (non-ferrous, for Aluminum 356, 5 gallons)
    Wet-It Wetting Agent (wash over wax to help slurry adhesion)
    Fused silica sand A (1 bag)
    Fused silica sand B (1 bag)

    I am casting in Aluminum 356 because it's an alloy designed for casting and (at the moment) can be easily and cheaply procured on eBay.

    My process for casting smaller parts is described here: https://github.com/01binary/investment-casting. This includes links to where I bought all the supplies and tools including the metal stock and the wax.

    The wax is from Remet Corporation, they call it Castwax One Pastille, sold in 50lb bags. They charged me $154.50 for the bag and $60 for shipping.

    Al203: The patterns were 3D-printed with online service from Protolabs, using Accura Xtreme White material similar to ABS plastic. After printing I spent a year polishing parts with 7 layers of Tamia high detail modeling primer and several grades of sand paper. Then I used SmoothOn DragonSkin to make silicone molds from the polished parts, and poured wax into them while degassing inside of Across International vacuum oven. Pour and mold temp are both around 700 F: adjusting for 20 seconds of transfer/pour time the actual pouring temp is probably 100 degrees lower. I perform the burnout in an electric kiln from Rio Grande.

    My vlog is at https://www.youtube.com/channel/UCj5SlpoLAmB8FrhlzKMdD3g

    My project logs are at:
    https://www.therpf.com/showthread.php?t=212832
    https://hackaday.io/project/19830-elysium-max-exoskeleton

    Thank you! Please let me know about those two questions (what does it look like to feed at the bottom, and if my material list from R&R is complete, whether I need Wet-It wetting agent).
     
  7. DavidF

    DavidF Administrator Staff Member Banner Member

    You got it! the vents would connect to the part where any air bubbles may get trapped and then up to the pouring cup.
     
  8. Jason

    Jason Silver Banner Member

    If I was going with shell, I would sprue those J-gate style vertically. Large sprue on the side that feeds the bottom. One thing with pouring aluminum into shell is ya gotta nail down a shell temp. Bronze is easy, get the shell around 1700 and be pouring bronze in the next 2mins and it's fine. I don't think aluminum is the same animal. I talked to a chick last month at R&R and she was a space cadet. Everything I asked her, she had to defer to someone else sitting in the room for the answer.:mad: Nothing like confidence from your tech dept. Anyways, seemed to them any temp was fine for pouring aluminum, I think that's BS. If you pour aluminum into shell, something in me says AFTER vitrification, a shell pouring temp around 1000 is plenty. Some areas of those parts look thin to me. I trust nothing on that is less than 3/16" thick right? If there is, an increase in pouring temps or shell temp might be in order to prevent freezing before filling. Toboho motts dogs would be a great example of this. He couldn't get aluminum to completely fill some thin areas, but that was sand so I'll stop there. I re read your post at the top and you said a problem you have is you can't get it to polish? Looking at those aluminum pieces above, the stuff looks like zinc! Weird. I do ZERO ph testing and don't even own a zahn cup. That one bit me in the ass recently, but I'm working on it. I've learned now after dipping parts in the bucket, I take a credit card and squeegee the stuff off the walls of the bucket and drop it back into the slurry. This keeps you from getting crust on the sides. It doesn't really matter, but the crust dissolves again back into the slurry with some mixing. Ph will not change much with dipping and you should be fine for pretty much the entire bucket. I'm on my first bucket and you cannot imagine how many times I've dunked stuff in that. Yeah I can feel some silica floating around the bottom. When I get to about a 1/4 left over, I'll pull it off and add it to some new stuff. For now, let's go with the zr slurry was probably the cause of your issues.... Thanks for the info on the wax. I'd like to try a couple lbs and see how it sculpts. It's crazy how they can engineer waxes for certain uses. That is some fine wax work and you can really see the time put into the original pattern. Gives them a cnc'd look without the cost that's for sure. I think the wet-it agent is a good idea if it's not stupid money. I know there was some household item that does the job, but if the pallet it heading your way, might as get the real stuff.;)

    Here is a quick sketch what I'm thinking. The tiny vents are there just to help support the piece.
    15306383467668147232820277392866.jpg


    I had a couple minutes to look through that 11page monster thread and the shear VOLUME of these pieces knocked me outta my chair. This is a super cool project and you are EXTREMELY ambitious to want to cast all of these in aluminum, but I gotta get this one question out there.... Had ya thought about casting them all in plastic and then send the entire lot out to be plastic chrome plated? I didn't get much reading done over there, but saw some serious photos. If I had to polish all that aluminum, it would take me the next 20years to attain what some plastic chrome platers can do in a day. Old cars back in the day had lots of plastic crap parts that were chrome plated. The process is still done today and it's not super expensive either. Much cheaper than all the sand paper, rouge and buffing wheels you are going to need. Not to mention the thousand of hours breathing that shit too.:eek: You know me by now, I'm not trying to pee in your cereal and want to see this thing in real metal, I'm just thinking aloud...;)

    This photo gives me nightmares! And you have how many band members? OMFG! lol
    [​IMG]
     
    Last edited: Jul 3, 2018
  9. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    01, welcome to the forum. That is a very ambitious project. The time modeling, process development, equipment investment, and just general commitment four years on......very impressive. Good luck with developing the shell process. It will be interesting to see how the surface finishes compare to the jewelers' investments.

    Best,
    Kelly
     
  10. 01binary

    01binary Copper

    Thank you! Jason, I see that you have a vent going into the pouring cup - does that mean I have to be careful not to fill the pouring cup with metal, because it will prevent gases from going out of the vent?
     
  11. Jason

    Jason Silver Banner Member

    Nahh.. I just dump in and aim for the bottom. Attach that vent at the top of the cup. Shell and solid block investment is gas permeable so technically it's not needed but I do it anyways. Do you have all the other bits already cast? I like what I saw in that photo with the satin finish.
     
  12. 01binary

    01binary Copper

    I am going to cast about 26 parts (out of 245) and fast-track the rest through CNC. It's kind of a balance: I want to be able to cast any part I want using either jewelry or shell process, but some parts are worth casting and some are easier to send off to a machine shop.

    The CNC quote for the three red wax positives above came out to $6k because of the complicated geometry. They can't machine them as-is, so I would need to split each of them into two, then devise a way for them to be screwed together seamlessly, then pay $1k to machine each split piece. I don't mind the price necessarily but I don't like wasting money, because it means I can do less cool projects. I still have four more exosuits (different style) on my bucket list, plus custom double-neck headless guitars, plus a drumming robot, etc.

    This project is the exosuit for the first guitarist...

    Exosuit concept for the second guitarist:

    [​IMG]

    Exosuit concept for the bassist:

    [​IMG]

    I am doing these in metal because I can't take plastic seriously. It would deform from heat, burn, crack easily, wouldn't have the satisfying clinking sound on self-collisions, or the cool weight. This is not a conventional cosplay project so I don't want to treat it like one - metal parts still tend to be taken seriously.

    Lastly, I am going into robotics and the CNC cost is one of the larger obstacles on the way to creating a robotics startup with no investors and no capital. Just one custom motor for a quadruped robot (like the Cheetah) costs about $200 - if you get all of them, plus the computers, plus spend the money to CNC all the parts it would take several years just to make one.
     
  13. Jason

    Jason Silver Banner Member

    Ya had me worried. 26 parts is doable. Shell casting 245 pieces times 6layers of shell is 1500 dips. :eek:

    Whats the plan for final finish? I like the bead blasted look, but it leaves aluminum porous and it doesn't retain that look for long. Naturally occurring oils in skin will leave finger prints when handling it unless it gets sealed. Going mirrored high polish on these parts would be damn near impossible due to the detail. Actual chrome plating on aluminum IS possible, but comes with it's own set of problems. Anodizing cast aluminum can be a royal pain, but might be another option. Lastly, powdercoating, but you haven't lived until you have the job of dealing with outgassing.

    I'm curious, what did your program estimate the total weight of all these parts would be? I use autocad and it gives part weight when given the chosen material.

    Not knowing what kind of shop setup you have or the availability of 3phase power, 6 grand for those 3 parts is ludicrous. I've seen Haas VF-0 vertical cnc machines sell for 10 grand. You'd be years ahead if you owned something like this. https://trademachines.com/haas/vf0 Given my choice of cast parts vs cnc milled, the answer is obvious.
     
  14. 01binary

    01binary Copper

    For anyone interested, R&R told me that since SuspendaSlurry FS already contains a wetting agent, I can make a small batch diluted with water and pre-coat with that before applying the primary coat. The pre-coat will need just enough time for a complete drain ("a couple of minutes") before the primary coat with un-diluted slurry is applied. They also said the Wet-It Wetting Agent can itself be diluted with water to do the same kind of pre-coat, and that may help more than diluting the full slurry with all the other components in it. I decided to play it safe and order Wet-It since the price was around $150 and the gallon jug should be easy to store.

    Jason: I am planning on either "indoor" powder coating or spray-paint with high-detail modeling paint in-house. I tried regular outdoor powder coating, and it completely destroyed the few parts I sent in because it erased all sharp details and wouldn't adhere to others. I will call some places and ask if they do the extra-thin indoor coating.

    Do you have a personal experience with a CNC machining center? I had a coworker with a Tormach, and he almost fainted after taking a look at the parts I got back from Protolabs. He said it would take him a few months to figure out what tools to use (and order more tools) just to make one of the parts, due to geometric complexity. It's possible that as long as I don't waste tons of budget on CNC'ing a small number of parts I could easily cast, the rest is well spent because I am paying for someone else to go home with a headache and maintain large machinery that could take weeks to fix when it breaks down.

    Inventor says 7.044 kg (Relative Error = 0.312850%) for the weight of the whole assembly. My heart dropped when I clicked Update on the Physical tab, but somehow it didn't crash. This is believable, but does not include the weight of the fasteners and hydraulic pistons, which will probably be 200% of that. I remember when I was prototyping with cardboard, I got really weighty parts which were essentially paper, but all the steel metric screws were super heavy.
     
    Last edited: Jul 5, 2018
  15. Jason

    Jason Silver Banner Member

    I KNEW there was a reason I didn't use that pre wetting stuff. Thanks for reminding me. If you need to remove powder coating off a part, get some Aircraft Remover paint remover. It might save your parts. PC does not sand blast that easy, it will, but can damage your parts. No such thing as thin powder coating that I know of. You have to spray it to a certain thickness in order for it to flow together when it hits 400. (I do powder coating at home too)

    Yes I've spent a bunch of time working with someone doing cnc. You are right, it can be a major PITA unless you do it regularly. Nothing is cheap thats for sure.
    I run inventor also and it's usually not far off with weight estimates from our experience. 7kg is not horrible, not light either. Let's see what kind of shape the band is in at the end of the night? lol
     
  16. 01binary

    01binary Copper

    I started with the two smaller parts, and I decided to place them flat under the pouring cup, so that they won't need supports when it comes time to actually pour the shell (they won't tip over if placed on the ground, may just need a little extra support to avoid tipping with metal in the cup). I noticed your drawing had (admittedly a different part) attached to the pouring cup length-wise instead. Is there a specific reason for this (am I setting myself up for a failure)?

    [​IMG]

    Here's an interactive model for this part: https://github.com/01binary/elysium-max-exoskeleton/blob/master/print/ChestPlateLeft.stl

    ...and the other part: https://github.com/01binary/elysium-max-exoskeleton/blob/master/print/HipLeft.stl

    I still intend to follow your exact drawing for the larger part above.
     
  17. Jason

    Jason Silver Banner Member

    Hmmm.. Reason to cast vertically instead of flat? Good question. Surface finish can be affected and I believe it also keep the "front" of the liquid heading in the right direction. Any more than that and it's dumb looks are still free from me. :( I would have still run that piece above vertically kinda like my sorry ass drawing. Also, sometimes, it's necessary to stick wax legs off the plumbing job to help it stand. I like one big fat ass sprue that leads all the way to the cup. Even if it's 14inches tall, this will provide head pressure to keep bronze going in the right direction. Now that I said that, I have probably cursed my latest shell job. It's vertical, but man has it got a lot of stuff going on. Hoping like hell I don't have stuff not fill. Thats the worst!

    Something else I am seeing with your above job that I'm not crazy about... I think shrinkage could be a problem with those skinny legs feeding a fat part. I don't mean to pee on your parade, but I would cut that thing apart and try again. I can't see how thick that thing is on the right side and if it's what I think it is, you'll end up with a hot tear at the skinny junctions or shrinkage. Caveat, I've only been doing this for a few years now, but it's all learning for most of us and that's why we are here.

    Let's see now if the peanut gallery is seeing what I'm seeing. ZAP???? ARTOPSY??? <<<<<<< He's been kinda busy, but hopefully he will chime in.
     
  18. 01binary

    01binary Copper

    Yeah today was rough and I never got to dipping. I'm sure it's for the best, I kept having the feeling that I will have to re-sprue so I will follow this advice.
     
  19. Jason

    Jason Silver Banner Member

    Don't fret. I post my tentative sprue jobs here too looking for feedback. Here is my first go. Look at the pathetic vents on the legs of this jewelry box.

    S3.jpeg

    The corrected version.
    S5.jpeg
     
  20. 01binary

    01binary Copper

    Here's another sprue proposal for both parts, please review and I will implement this Saturday:

    https://github.com/01binary/sprue-planning/blob/master/chest-sprues.stl
    https://github.com/01binary/sprue-planning/blob/master/hip-sprues.stl

    ...I left some of the sections thin, because if they attach to the cosmetic surfaces of the parts (they would have to, if they need to be on the "top" surface going up) then they can only be as fat as the feature they attach to. I could make all of them thick if it's fine to attached them to the side surface.
     
    Jason likes this.

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