Automotive Rear Upright/Wheel Carrier

Discussion in 'Lost foam casting' started by Al2O3, Nov 25, 2018.

  1. ESC

    ESC Copper Banner Member

    Same here David. Especially with x, y .and z DROs. The part is made before the computer boots up although not in multiples.
    Sorry for the hijack Kelly.
    DavidF likes this.
  2. oldironfarmer

    oldironfarmer Silver Banner Member

    I'm a novice, but using Fusio360 and Mach3 on my CNC router it cuts foam like a dream. But I'm not good enough with Fusion360 to make fast work of it and don't have enough work to spend the time studying yet. My software has never failed and I can run overnight programs unattended. Flat items are easy but the stepover Kelly mentions eats up the time on curves.

    I think Kelly is right on target with what he is doing. I'm really enjoying the show.
  3. garyhlucas

    garyhlucas Copper

    Yes CamBams 40 session tryout is very generous. I bought my copy because I did so much machining during the trial it felt like I was stealing it! I bought another copy for the big CNC bed mill at work. Does everything we need and it gets used almost everyday for one offs. 10 pieces is a big run for us.
  4. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    All four of the new patterns are now detailed. I attached the bobs and sprue same as the previous pattern. The bobs make good feet for drying the pattern. I slush coated the interior cores the same as on previous pattern. I wanted to dip coat the entire pattern but it’s large enough that it would have required nearly a 5-gallon bucket full of slurry. After experimenting on some scrap foam, I decided I could just brush the drywall compound that had been thinned to dipping consistency.

    I don’t think this would have been possible without the addition of Dawn dishwashing soap to the slurry to act as a surfactant. Not only does that make it wet the foam and wax features well, it also seems to help the slurry flow and self-level. When I had previously tried drywall compound thinned to this level, I could hardly get it to cover the foam let alone the wax. With both foam and wax being so hydrophobic the watery mixture would tend to puddle instead of laying down on and covering the pattern. During the previous attempts I used Ethylene Glycol (automotive antifreeze) as a surfactant which was not nearly as affective. This time I added a small amount of Dawn, a puddle about the size of quarter on top of a 12-oz cup of thinned drywall compound and mixed it into the slurry.

    This was a bit of a wow! The slurry behaved very differently….for the better. I was surprised by how well it applied, looked, thin and uniform thickness. Seems like it should be significantly more permeable. Here’s a picture wet. You can still see some of the pattern seems and surface details through the coating. If it was dipped, it’d take a few seconds to dip it and then a couple minutes to tilt and reposition it as it shed slurry before placing it to dry. Brushing with the thinned slurry was still very quick.

    59 Wet.JPG

    I dried the part the same as last time……sitting over a furnace floor vent in my house overnight, capped with a vented cardboard box. Simple, and as long as it’s Winter time, available. Here’s a picture dried.

    60 Dry.JPG

    I looked it over very closely and briefly considered a second coat on the exterior but decided to stay with one very thin coat. I packed and prepped the mold identical to the previous attempt. Same pour temp 1575F. Here’s a list of changes.

    1. The previously noted pattern changes, most notably, repositioning the internal core windows to very highest point of the cores.
    2. Thin coating applied as discussed above both inside and out.
    3. Used A356.2 Ingot with TiB and Sr added. It was a nice looking melt. Started with very clean crucible.
    Here’s the result for attempt #3. First, just as it came out of the mold and water quenching.

    60.1.JPG 60.2.JPG

    The black polystyrene residue is light on the bottom side and seems to be concentrated on the top surfaces, increasingly as you near the sprue. It doesn't seem to have any appreciable affect on the casting. I don’t know what commercial aluminum LF castings look like coming out of the mold media. I’m going to give this more thought as to whether I could pull more gas off with a little vacuum. However, I don’t know that I’m going to do any better. I did a quick clean-up job it up with a stainless wire brush to get a better look.

    As near as I can tell, this casting appears to have accurately reproduced every feature of the pattern without any obvious visible flaws. The thin coating was still adequate and produced a surface finish as good as any of the thicker coatings I’ve used.

    61.JPG 62.JPG 63.JPG 64.JPG

    Between feeling with finger tips, line of sight, and use of light and mirror, I inspected all the cored areas. They’re all fully formed and the cores have remained completely formed and stable. The previous problem area was completely remedied by repositioning the internal core windows. It’s hard to show but here’s best I can do with a couple photos of the casting interior.

    65 Internal Core.JPG 66 Internal Core.JPG

    I’m going to take it to work and media blast it. This one may be usable. I think I’ll cast at least one more before making any decision to cut it up. Still have to get through heat treating too, but might have this one whipped boys.

  5. oldironfarmer

    oldironfarmer Silver Banner Member

    Congratulations! Great work!!

    I may try more Dawn. I have been using just three or four drops in about 12 oz of mud, and that fixed my wax covering issue but still would not dip. I guess you had no ill effects from a lot of soap.

    It is an amazing process.
  6. DavidF

    DavidF Administrator Staff Member Banner Member

    I'm still amazed at how well lost foam has been working out for you Kelly.
    Looking forward to the next magical feat.
  7. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Thanks OIF. No ill effects as far as I can tell. Quite the contrary. I let the cup of thin slurry sit for a week and it looked like the Dawn was sitting on top but re-suspended with a few turns of a stirring stick. No vacuum degassing or anything fancy.

    I continue to push the process as far as I can.....just can't seem to get off the lost foam highway....Lol

    Couple other details. It’s the same weight as previous pour at 7.75lbs. I had 11.6lbs before skimming. If I take away the pigged off ingot and the 1/2lb or so I dribbled around the pouring cup, the casting, sprue/gate, and cup were right at 10lbs. Outside chance I could pour this with a brim full A10 but if my aim wasn’t perfect or burped a little out of the cup, it might pour short……I’ll stick with the A20 and a couple pounds of cushion.

    67 Weight.JPG 68 Total Weight.JPG

    When I poured this time, there was no mid-pour (small) burp back through the cup as there had been in previous two pours. My pouring cup is 2 ½” diameter by 5” tall. It’s a little small for this size pour. When you first fill the cup and hit that lost foam pause, you really need to have the crucible tilted and be right on top the cup waiting because once a part this size starts drawing metal again, it empties this size cup very quickly. I was able to maintain continuous feed with minimal spillage around the cup….maybe ½ a lb. A 3” diameter cup and another 1” of depth would make for a little more relaxed and worry free pour.

  8. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Been looking at how to dip coat this without making up 5 gal+ of slurry. Problem is, it’s big! As it sits it’s 13”L x 8”T x 9”W across the brake caliper wings. Here it is with a 12” Rule.

    69 Scale.JPG 70 Scale.JPG

    When I attach the gate and sprue, which need to be there when it’s dipped, it gets 4” taller. I could try to dip one end at a time, but not sure that saves me much. It won’t fit in a 5-gallon bucket with sprue in any orientation. I’d like to dip it as it sits holding onto the sprue. Might take a cardboard box, glue in cardboard baffles to take up space and line it with a garbage bag. Or just stick with what I’ve been doing. Hmmmmm.

  9. oldironfarmer

    oldironfarmer Silver Banner Member

    I've thought about a small trash can, I think I've got a ten gallon one (no, it doesn't make a good hat), and the trash bag will seal moisture in if you close it right. One of my concerns is bacterial growth, or mold. That would make a big mess to get rid of. My little quart brush on container is getting a little color above the liquid line so I think it needs to be cleaned out. I think your current plan is pretty nifty.

    I had a comment on your Dawn concentration. If you're getting color on the top after it sits you might get by with less if the Dawn has the liquid over saturated. My much less concentrated mix never gets any Dawn color on the surface after sitting.

    Once again, very impressive results.
  10. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    I'd think the addition of a small amount of bleach would fix that. Might need to test the styrene and somewhere rattling around in the back of my mind, I recall something that is added to PoP as a retardant to slow cure. Was that bleach? Ammonia? brain fade.

    No color. Didn't feel like (pure) Dawn....diluted Dawn maybe.....but it very well may be over dosed. If so doesn't seem to be a problem unless those biodegradable surfactants Dawn says it contains grow mold. I had a coating homebrew that had Dextrin in it.....that grew mold. I don't recall if it was just to make it thixotropic or if it was to keep things in suspension/solution (Deflocculatent) like CMC/Gum Cellulose.

    Thanks OIF. I'll keep workin' it.

  11. DavidF

    DavidF Administrator Staff Member Banner Member

    Its acetic acid to slow the cure. Bleach might actually speed up the cure, but dont quote me on that one. I know calcium chloride will, but does a chlorate?
  12. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    I did some light web surfing and saw claims that citric acid, vinegar, & ammonia were all retardants too. Cold/Ice water will slow things up. Even if bleach was a retardant, I suspect a very small amount added to the drywall compound would inhibit mold growth and have little affect on the drywall compound. The premix doesn't kick anyway.

  13. JoeC

    JoeC Copper

    One new benefit of membership in the American Foundry Society is free complete access to over 100 years of technical research

    I can't seem to attach full pdfs of articles, size is too big

    mek props.jpg

    This was a very well done piece of work, some key points are

    The purpose of this paper is to demonstrate, both experimentally and analytically, an inevitable fact: properties vary substantially throughout a casting

    Quite expectedly, properties were shown to vary widely within the casting; the actual mechanical properties were significantly different from the “textbook values” usually based on measurements carried out on separately cast tensile specimens such as those conforming to standard ASTM B108.

    Designers usually do not fully understand that it is impossible for a foundry to provide “handbook tensile properties" at every location throughout the casting, as can be done for wrought products.

    This can lead to a great deal of confusion among casting users as they will be given a range of properties for the same alloy depending on the supplier, industry professional, or handbook consulted.

    They will often conclude that a design value one can trust does not exist.

    It is the role of the foundry to explain this fact: mechanical properties in castings not only change with the process but may vary within the same casting.

    For instance, in the casting which was investigated in this work, the elongation varied from 2.1% to 8.0% depending on the solidification conditions at a particular location (solidification time and temperature gradient).
    (exactly what I have found testing castings over the years)

    The casting should be designed with the full knowledge of this fact

    Variation in properties doesn't mean it is a bad casting - far from it

    Years ago we tried to get some automotive work and were able to quote Aluminum engine mounts for Corvette

    The requirement was 7% elongation MIN which I knew was not possible

    So I bought a half dozen engine mounts from the local GM dealer to test

    When I went to pick them up there was a note for the parts guy to call the owner to talk to me

    He was really concerned about "my vette" and offered to work on it no charge - said he had never sold an engine mount in his career let alone 6

    He laughed when I told him what I was doing

    We cut test bars out of these parts and no surprise most failed minimum elongation

    When we presented this to GM the room went dead silent and one of the big dogs looked at his guys and asked "are we in a recall situation here?"

    They looked at the warranty history and there were zero field failures and because this was back in the day when GM had actual engineers (not MBAs) they immediately realized they had a case of unreasonable tight specs loosely enforced

    One test fell below minimum but, the part as a whole was up to the task

    They let us run with 3% MIN elongation with a promise to work to improve over the program life (which we did, I think we got real close to 7% AVG after a lot of work)

    Sadly it is rare to find reasonable engineers with a feel for the process and parts, most are trained just to say "make to print for less than the China price"
    Tobho Mott and Mark's castings like this.

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