Bending thin plate in a large radius using weld beads?
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  1. #1
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    Default Bending thin plate in a large radius using weld beads?

    Hi guys,
    I am working on the design of a machine (onsey-twosey thing for in-house use) that requires a thin-ish plate to be bent thru 180º with a large radius. Plate is likely to be 1/4" or 3/16" thick, bend radius will be about 6-8". I am not a fab shop or sheet metal shop so I'm trying to work out a way to do this with minimal equipment...

    Would running a series of parallel weld beads spaced apart beginning at the center of the plate cause it to curl up on itself like I want?

    Normally I would be worried about avoiding this kind of distortion but in this case I'm wondering whether it might be used to my advantage. The finish on the inside of the bend does not matter. Unfortunately I don't have a spare sheet lying around to just try this out on.

    I tried a search to see if anyone had tried this before but came up blank, maybe I'm using the wrong terminology...

    Thanks!
    -Aaron

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    Send it out.

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    Quote Originally Posted by digger doug View Post
    Send it out.
    Haha I knew someone would say it

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    I don't think you will be able to bend the plate it that tight of a radius with weld bead distortion. Maybe a 16" radius.

    How wide are the pieces? If they aren't very wide I would make a form out of steel or aluminum and heat the part to be bent. It doesn't have to be red hot steel starts to bend easier at about 1000F.

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    Quote Originally Posted by aarongough View Post
    Haha I knew someone would say it
    You can't doo everything.
    Seek out and PAY for expertise that you don't own.

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    I've done this lots of times for metal 6" wide or less using nothing more than a large hammer and wide open bench vise jaws or a quick V block of some bars welded parallel on a plate. Should take maybe 10 minutes to do the bend. Wear a heavy leather glove and use a pair of vise grip pliers to hold the piece with one hand while hammering with the other. A paper pattern on the bench you compare to helps.

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    Could you not slice a tube section? That would be my first choice, followed by sending it to someone with a roller. I doubt you will be satisfied with the weld bead method. I think it will bend unevenly. Just a tiny bit of uneven heat and I think you will get uneven curling, and probably twisting.

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    Heat straightening is commonly done to either eliminate distortion from welding or to curve parts as you are wanting to do. But it is quite an art and your odds are slim at getting it right on your first ...or 100th try. This really seems like something you should either send out for roll forming or see it as an opportunity to invest in a roll former yourself...

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    Sounds like a hot mess. Literally. Welding will not cause it to bend evenly in any direction. How big is the sheet you are trying to bend? What sort of equipment do you have access to (besides a welder)? There are lots of ways to bend things.

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    If your talking about welding down the length of the part it well shrink "BOTH" ways and end up looking like a football and not a tube ,,, you can do a lot of bending with a big torch and a wood hammer ,, I have build backhoe buckets that way and its not hard to do ,,, one just has to take it slow and control the bend with the torch.

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    You might be able to get this done with a torch, but it would be time consuming and prone to "football" style errors as mentioned above, which would require heating in different areas to correct. I'm guessing it would be somewhat like trying to herd cats.

    Moving steel with heat works better if you can get the heat into a concentrated area as quickly as possible. You need very rapid localized heating to get maximum movement, which you'd need for something like this. I might be inclined to try a TIG torch for the heating if I was going to try it. But I'm with the others, I wouldn't try it. Too much of a PITA. Find someone with a roller.

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    Thanks for the responses guys! As suggested I will shop this one out!

    I hadn't thought about it distorting like a football, makes sense! Glad I didn't try that one!

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    Find someone with a slip roll. It has two rollers that grip the metal like a washing machine wringer and a third roller that can be adjusted for the amount you want the sheet to bend. You can sneak up on the radius you want by moving the third roller in small increments.

    the term "slip roll" comes from having the top roller released so the finished part can be slid off the end.

    A big deal for an amateur beating on it with a hammer, trivial to a proper sheet metal shop.

    Bill

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    A roller will leave a straight section on each end. The length of the straight section will depend on the size of the rollers. For a half circle, the easiest way around this problem is to start with an over length blank, and trim both ends.

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    Quote Originally Posted by gbent View Post
    A roller will leave a straight section on each end. The length of the straight section will depend on the size of the rollers. For a half circle, the easiest way around this problem is to start with an over length blank, and trim both ends.
    I need a 6" straight section on either end of the bend anyway so it should work out fine!

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    Quote Originally Posted by gbent View Post
    A roller will leave a straight section on each end. The length of the straight section will depend on the size of the rollers. For a half circle, the easiest way around this problem is to start with an over length blank, and trim both ends.
    If you bend it a little at a time and feed it in from both ends it will bend a fairly uniform arc.

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    Quote Originally Posted by carlherrnstein View Post
    If you bend it a little at a time and feed it in from both ends it will bend a fairly uniform arc.
    Please explain. Whether it's an initial pinch or a piramid roll, no bending takes place until the sheet contacts the third roll. Yes, you can use the initial pinch rolls as a vise and horse the bend on thin sheet but you better be a pretty big fellow to bend very wide 1/4 this way. If I've missed a technique I'd like to know.

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    Did I miss the part about how long the piece is? Different methods depending on length of part.

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    The way I set a slip roll up is to adjust the "driving" rollers to the point they pinch the metal being bent. The third roller is adjusted up after the piece is run through both directions. If it needs to be pretty round you cannot move the third roller up much because it will not be uniform towards the ends.

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    not an in-shop method, unless you have a press brake, and if you don't need the near perfect radius at the bottom, would be to use a press brake, if the final shape is "U", you'd start with small creases near the vertical sides and leave the bottom ones to be done last, any reasonable brake with standard tooling will work for this, 5min to test the crease depth and distancing to get the final radius and 10 more min to mark your part and bend it

    but, as mentioned in post #7, splitting a pipe and welding on the straight sections is probably the easiest

    added bonus of using the press brake method, when someone asks you how you did it, say - the same way they do Atlas V rocket fuel tanks!

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