Welding steel bar stock for milling?
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    Default Welding steel bar stock for milling?

    When cutting a piece that requires a lot of removal, for example a long U shape. Does it ever make sense to weld two or three pieces of bar stock together to start with? Or are there too many issues with material defects, stresses, etc?

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    no, and yes, with exceptions.

    to start with, the strength, particularly fatigue strength, will be inherently inferior due to the interrupted grain structure of the part.(particularly on a cyclically loaded "U" shape, where the weld would be at a zone of high stress)

    second, the chance of defects being introduced by the welding process, particularly in the HAZ, such as hydrogen embrittlement in "carbon steels" for just one example, is significant.

    third, the residual stress from the welding process is considerable, the nature of molten metal solidifying rapidly makes this basically inevitable. the dimensional stability of a weldment upon machining is an unknown. to put it simply, "shits gonna move".

    yes, with a stress relive or an anneal, the 2 and 3 would be minimized, but the basic discontinuity of the grain structure will remain.

    it only makes sense in certain rare materials or on parts of large dimension where raw materials are unavailable or cannot be preformed by better methods.

    for example, for a "U" shape, bending is a far, far superior way to preform a part for machining. way better even than cutting from a solid plate for a number of basic material science reasons.

    hope that makes sense!

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    cyanidekid is correct, but maybe a touch too discouraging. Weldments have largely, or entirely, replaced castings in many industry sectors. Both weldments and castings are intended to put the metal where it's needed so very minor metal removal is required, compared to starting with a solid block.

    But a lot does depend on the quality of the welding. Inclusions, incomplete fusion, etc. will doom the weldment, and that's before you get into questions about HAZ and so on. If you are working with anything other than mild steel, proper welding processes including preheat and interpass heat must be followed.
    Last edited by sfriedberg; 04-29-2020 at 04:56 PM.

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    Quote Originally Posted by mteiken View Post
    When cutting a piece that requires a lot of removal, for example a long U shape. Does it ever make sense to weld two or three pieces of bar stock together to start with? Or are there too many issues with material defects, stresses, etc?
    Post up the print.

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    Quote Originally Posted by cyanidekid View Post
    no, and yes, with exceptions.
    I am so stealing that.

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    Quote Originally Posted by Mud View Post
    I am so stealing that.
    I believe Pat Paulson invented it.....

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    Quote Originally Posted by sfriedberg View Post
    cyanidekid is correct, but maybe a touch too discouraging. Weldments have largely, or entirely, replaced castings in many industry sectors. Both weldments and castings are intended to put the metal where it's needed so very minor metal removal is required, compared to starting with a solid block.

    But a lot does depend on the quality of the welding. Inclusions, incomplete fusion, etc. will doom the weldment, and that's before you get into questions about HAZ and so on. If you are working with anything other than mild steel, proper welding processes including preheat and interpass heat must be followed.
    post weld stress relief is important also if tolerances are tight, and especially if the weld is in the cut path.

    yup, its done all the time for larger more complex parts especially, so guess I was addressing the OP's example of a "U" shape mostly.. (the title does say "bar stock")


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