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  • How to achieve a good looking aluminium die casting?

    Discussion in 'Metal casting & moulding' started by GarethW, Mar 9, 2012.

    1. GarethW

      GarethW Chief Clicker Staff Member

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      Currently we shot-blast a texture on our aluminium die castings to make them look nice.

      This does a reasonable job of making the appearance look OK. However, the disadvantage is that if you use too much blasting you get peel, and if you use too little it still looks terrible. It's a fine line.

      Can anyone think of a better process solution to make a die casting look OK?

      IMPORTANT NOTES:
      • It must be a low cost process!
      • It must not involve paint.
      • The surfaces must be electrically conductive afterwards
       
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    3. vic.blackall

      vic.blackall Well-Known Member

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      There are several methods of surface cleaning parts, shot blasting being one of the most aggressive. I would suggest having your aluminium parts Vapour Blasted. This process is is less aggressive and leaves the surface with a satin type sheen.
       
    4. GarethW

      GarethW Chief Clicker Staff Member

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      Hi Vic, thanks for your reply. What's your view on chemical method - chemical polishing perhaps?
       
    5. vic.blackall

      vic.blackall Well-Known Member

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      Hi Gareth, I have not had any experience with chemical polishing processes. I guess that your die cast finish is devoid of any marks, as would be evident in machined parts, if it did I would think that the chemical process would not remove these type of machining marks. A cautionary note that any surface treatments will affect any tolerances that you might want to maintain unless they are masked.
      From memory silicon, is added to aluminium to improve it's flow characteristics when casting, this I believe might give problems with certain chemical surface treatments. I think that you would need to advise the process company as to the chemical composition of the aluminium casting just in case of any adverse chemical effects.
       
    6. GarethW

      GarethW Chief Clicker Staff Member

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      Thanks for the feedback. Yes I agree that the chemical polishing might affect tolerances. It would probably also play havoc with features like screw threads. Masking so many features could be a bit of a nightmare. Chemical polishing does not feel like the way to go for so many reasons, but I thought I'd bring it up anyway.

      Just wish I could think of a few more options....
       
    7. stewlenox

      stewlenox Active Member

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      How about vibratory abrasive finishing, followed by shot burnishing?
       
    8. GarethW

      GarethW Chief Clicker Staff Member

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      Thanks for the suggestion. I'm not that familiar with these processes. Are they relatively common/cheap? How does shot burnishing differ from shot blasting as a process. Is it the same kind of thing but with less abrasive particles?
       
    9. vic.blackall

      vic.blackall Well-Known Member

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      How big are these castings and what are they used for?

      As said before they could be vapour blast and then clear lacquered or if not too large anodized clear, or coloured.
       
    10. stewlenox

      stewlenox Active Member

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      Hi Gareth,
      Shot burnishing is when polished steel shapes are used in a vibratory tumbler, usually with some kind of lubricant like soap and water. They burnish or planish the part by rubbing against it.
      You can get many kinds of abrasive media for these tumblers...everything from ceramic abrasive to rubber bonded shapes. The gun reloading guys use walnut shells to clean their used cartridges prior to reloading.
      Check out the Gesswein company, or Rio Grande Jewelry supply for starters. I'm guessing that a google search will yield more industrial sources.
       
    11. wizardofid

      wizardofid Active Member

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      What process do they use to finish the iPad and the Mac Book Pro?

      Just thought I would jump in with a related question. How do they get the milling marks off the ipad and MacBook Pro shells, AND get such consistency on tight tolerances?
       

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