3d Printer Extruder Mount with Polycast

Discussion in 'Lost PLA casting' started by Mach, Jul 5, 2020.

  1. Mach

    Mach Silver

    As the saying goes, experience is what you get when you don't get what you want. This posts shows two failed attempts to cast a 3d printer extruder mount. Third times the charm (fingers crossed)

    The mount is designed to fit a MakerGear M2 printer with a Bondtech BMG extruder and v4/Copperhead hotend.

    [​IMG]

    First attempt
    Long story short - I underestimated how long a 5" flask takes to cool down. I pulled them directly from the kiln at 730c. The aluminum sat molten for at least 30 minutes in the flask if not longer. Definite face palm moment.

    Lesson learned pour at most 500C if not cooler. Any advice on this one is appreciated. On a positive note, I believe the polycast did burn out completely due to a crazy long burnout. Another lesson learnt was a 3d print for plastic is not the same as for metal casting. I eliminated the blind holes for the second attempt and sprued to make clean up a little easier.

    On to the pics. Porosity, hot tears and shrink defects...
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    I did finish the bottom one despite the porosity in the lower arm but its about a 1 mm off on alignment. Second attempt.
    [​IMG]

    Second attempt
    Long story short, poured too cold. I poured the first flask and then attempted to pour the second without reheating. It also looks like burnout wasn't complete. I printed with too many shells and the burnout wasn't long enough. My kiln had a couple of problems that shortened burnout. I'll keep experimenting with the polycast but I think I'm going to try an open mold burnout next and a sand cast combo like MyFordBoy did here. With the part geometry, it should work.



    Here's the second attempt

    3d printed in Polycast and smoothed for 30 minutes.
    [​IMG]
    Note the two vugs on the bottom. Given the visible layer lines, I think that's remaining plastic. Fewer shells next time and a more reliable burnout would help.
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    I sprued through the center hole to make sure I didn't lack for feed metal. I did not connect the center sprue to the mount other than through the top legs.
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    The mount did not fill completely around the center hole.
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    Surface finish was good for my second attempt but I hope to get better in the next casting.
    [​IMG]
     
    Last edited: Jul 5, 2020
  2. Al2O3

    Al2O3 Administrator Staff Member

    Maybe too short. I see reference to shell and burn out but maybe a little more information about shelling, burn out, mold condition/temp and metal temp at time of pour.....inquiring minds want to know!

    Best,
    Kelly
     
  3. Mach

    Mach Silver

    Sorry, good point, here's the rest of the story. It was invested with Plasticast in a 5x7" perforated flask. It was burned out using the following schedule:
    upload_2020-7-5_19-26-48.png

    The original plan was to cast at 500C but the temp of the flasks were much less than at 7am this morning. I did not measure the mold temperature. Mold condition was white as expected. I didn't measure the temp of the metal prior to pouring instead timed it 3 minutes after the last ingot melted. I skimmed the dross and used a vacuum pump on the first flask pulling between 20 and 25 "Hg. I had shut off the burner and replaced the crucible in the furnace after pouring - its an A6 and was half full. Then placed the second flask, this one, on the vacuum stand. When I skimmed the surface of the metal, it was dull not shiny, I chalked it up to dross. Thinking back, it looked like it was cooling and I should have restarted the burner. If I had measured the temperature, I would have known. The molds were left sit 15 minutes to cool and then dropped into water. They bubbled mildly from the hot metal but not near as violent as past pours.
     
  4. Al2O3

    Al2O3 Administrator Staff Member

    I'm very interested in aluminum shell and block investment, just not a current practitioner. I think David has commented several times he's had better results with the mold temp being more in the 500-600 F range for Aluminum. Was 500C the manufacturers recommendation?

    Best,
    Kelly
     
  5. Mach

    Mach Silver

  6. myfordboy

    myfordboy Silver

    I think an extended feeder like I used would improve things. You need more pressure to fill the mould.
     
  7. Mach

    Mach Silver

    Thanks for the advice. I'm using vacuum casting so I didn't think pressure would be a problem. If I switch over to sand casting with a plaster mold like you did, I'd add an extended feeder.
     

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