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  • Aluminum cast prototypes

    Discussion in 'The main mechanical design forum' started by GoodCat, Dec 4, 2018.

    1. GoodCat

      GoodCat Active Member

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      I want to share with you one simple way to get aluminum casting parts. :)

      When I need to cast 1-2 aluminum parts, I use a very simple method.

      Jewelers use the same method.

      The essence of the method of obtaining metal parts using standard abs plastic. The technique is called casting by burning models.

      Stage 1: The design of the object.

      Use any CAD to design the object.

      Stage 2: Adding a sprue.
      A sprue is a cone connected to a part of an object. Although the length, width and diameter should not be exact, it should be of a sufficiently large diameter for casting the liquid metal. In some larger objects, it may be more convenient to use multiple sprues.

      Stage 3: Increase by 2%.
      Using CAD, increase the model by 2%. Scaling an object by 2% across all axes will create an increase in volume of about 6%, which compensates for the shrinkage of the metal object.

      Stage 4: 3D print details with sprues.

      Use a 3D printer to print a 3D object. The sprue is usually directed upwards, but I recommend using a bottom filling, a sprue rounds the part and enters from the bottom, and from the top I make several small holes to remove air.

      This scheme allows to get less porosity details.

      Stage 5: Create a mix
      I mix fine sifted sand and epoxy that harden when heated and as a result get liquid mud.

      Stage 6: Create a shell

      I grease the part with a mixture with a brush and then dry it with a building dryer.

      According to this scheme, I apply 4-5 layers to get a wall thickness of 3-4mm.

      Stage 7: Remove plastic

      The melting point of the ABS plastic is 220 C, the heat resistance of the organosilicon resin is 300-350C. I heat the mold on an open fire and remove the plastic. The short-term temperature stability of the organosilicon resin is about 450-500 C, you can not be afraid to overheat. I completely remove the plastic and as a result I get a shell.

      If you have the ability to print parts not from ABS but from paraffin wax, it will be even better.

      Stage 8: Casting preparation

      I mix sand with used engine oil, quite a bit of oil in order to make the sand more viscous.

      I take a wooden box and pour sand onto the bottom, compact the sand and put a shell on it.

      I fill all the free space in the box around my shell with the same sand, leaving 10mm to the upper edge of the sprue. The mixture should be slightly compacted but not too strong so as not to break the shell.

      Stage 8: Aluminum casting
      I pour aluminum and wait for it to cool

      Stage 10: Removing the parts

      I take it as a sprue and take the aluminum part out of the sand along with the shell. I make several light strokes of the dural hammer on the shell and remove it from the part. Everything is ready, it remains only to cut the sprue.

      It is allowed to use a steel box and heat it all up before pouring aluminum to improve casting accuracy.

      This casting method is very simple and provides high precision parts.

      I hope my article was useful for you! :)

      Sorry for my english!
       
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    3. john12

      john12 Well-Known Member

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      This sounds like a great idea. It sounds very similar to the 'lost wax' technique, but by using 3D printing you can get a very detailed and accurate (and repeatable!) model.

      Can you share any pictures of stuff you've made with it?
       
    4. GoodCat

      GoodCat Active Member

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    5. john12

      john12 Well-Known Member

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      Wow, that looks great!
      Do you have to do much cleanup/post-processing afterwards? If so then what's the best way to do that? Do you have some kind of bead-blasting machine or can you do it by hand?
       
    6. GoodCat

      GoodCat Active Member

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      the shell is very fragile as I wrote earlier it breaks easily with light blows of a duralium hammer

      The shell is a sand with resin, hardened by temperature, so there are no sand particles on the cast.

      If you use fine sand, the quality of the casting will be significantly better.

      For casting on the photo used ordinary coarse sand.

      Yes, after casting, the casting has a matte color, the perfect way to clean it up will be blow with electro corundum sand.
       
    7. john12

      john12 Well-Known Member

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      So the actual part is quite fragile you mean? Could you actually use these parts in a machine, or is it just more visual?
       
    8. GoodCat

      GoodCat Active Member

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      I think that I did not correctly explain my thoughts.

      The shell for casting is quite fragile.

      The casting itself turns out to be of high quality, it is a high-quality casting method that allows to achieve high precision even with a fine fraction of high-purity sand.

      The part will be strong enough as if it was obtained, for example, by casting into a
      EN">gypsum
      color:#212121;mso-ansi-language:EN-US">
      sand form or steel form. Like any cast, it will be less durable than a forged part, but stronger than casting under pressure and also the probability to get bubbles in the metal is much lower than when casting into a gypsum, steel form or casting under pressure.
       
    9. john12

      john12 Well-Known Member

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      Ah, no, that makes sense - I think I just read it wrong!
       

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