Bead/sand blasting warp part?
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  1. #1
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    Default Bead/sand blasting warp part?

    I’m machining some parts, 6061 al, about 8 ft long, 2x3in crossection. They get lightening slots thru and some 2d profiling. The slots are 1-1/2” wide and 4” long, so that leaves a 3/4 thick web on either side of slot.
    About 12x 1/4-20 tapped holes and 3 reamed holes longways down the length.
    These parts are +/-.005 and fully inspected by my customer.
    We just did a good first article, but now my customer wants us to machine all profiles, then deliver so they can be blasted (finish required) then we will take back and D&T everything.
    Will blasting warp this thick of a part?

  2. #2
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    "Sand" .....sharp will doo less surface stress releasing than "bead" which
    is more round.

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    Much depends on the blaster Have your customer order them at that blaster You can do the machining for the blaster The rest is up to them
    Peter

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    I highly doubt you will warp aluminum 3/4" thick with a shop bead/sand blaster. Certainly not anymore than the machining of something that long will.

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    I asked customer and I think they said they are going to use 100mesh al oxide.
    They said they don’t think it will cause trouble on this large a cross section. But I wanted to bring it up beforehand anyway.

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    And who is going to eat the part cost when it does warp? That's a lot of surface area and I would proceed with caution.

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    I don't know what to tell you other than the fact that my customer spent DAAAAAYS straightening parts that they have turned and milled, I have EDM cut a few features, I've delivered,
    they've dimensionally inspected and subsequently sent out for glass-bead blasting to get a completely non-directional, uniform finish.
    Not a single one - out of a lot of 700+ pieces - stayed straight. Not one miserable piece!!!

    This was 347SST, approx 3/8 average thickness of no more than 1.5" long, parts moved no less than .015/side.
    You have 3/4 thick, but over 8'?

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    I make some parts out of 5/8 316 plate that warp like crazy during bead blasting. After a huge amount of bickering with the customer about it we told them that if we continue making them we are not going to bead blast them anymore. They finally agreed, no more bead blasting.

    My experience of blasting aluminium is more limited, but same customer likes aluminium weldments to be bead blasted too, and those definitely do move too, I just don't know how much.

    Anyway, I'm with Seymour. They want to bead blast them then fine, but make sure you get your arse covered in writing beforehand.

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    I'm with the "cover your ass" crowd, there's certainly a risk of warpage during the blasting.

    Now, if there's enough money in this project and there's a good reason, then a proper robotically controlled symmetric blasting could be done, so opposing sides could be hit uniformly. But this takes some real cost to set up and test.

    Is this for improving adhesion or similar purpose? A chemical milling and conversion coat might be safer.

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    I have had a crapshoot of results from blasting. VaporHone blasting has been much better in this regard


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