My tube keeps cracking!

  1. hooblah Member

    Messages:
    145
    south london
    I've got some 42mm tube with 2.6mm wall. I'm trying to flare one end into an oblong shape. Ive made a die using round bar which is used with a 20t press. The problem I'm having is the tube cracks, even after heating red hot!

    So the tube needs to be flared to this shape:
    IMG-20180103-WA0017.jpeg

    This is the die
    IMG-20180103-WA0001.jpeg

    And these are the results:
    IMG-20180213-WA0002.jpeg

    Would it be better if I used cds tubing?

    Also would it work better if I flared it out with a cone shape first to obtain uniform wall thickness, then hit it with the final shape?
     
  2. Seadog

    Seadog Forum Supporter

    Messages:
    1,966
    Location:
    NE London - UK
    Possibly a longer cone is needed. Also, don't heat it and expect to do it in one. it may need to be annealed a few times. Or perhaps the material just doesn't like being stretch like that. I'm sure someone will know.
     
  3. WorkshopChris Forum Supporter

    Messages:
    3,141
    Location:
    South East Essex
    Is that ERW tube? Ideally you need seamless drawn tube.
    You will need more processes than heating and pushing around a former in one go. Part of your profile needs stretching while other areas need shrinking as the shape develops.
     
    hunter27 likes this.
  4. Dutch Welder Member

    Messages:
    71
    Location:
    Oss, The Netherlands
    Could you not cut 2 curved parts from the tube for the sides, and just use a bit of plate in between?
    You'll have a hell of a time getting these parts formed from thickwall tube, as there is to much going on within the material
     
    hunter27, optima21 and WorkshopChris like this.
  5. hooblah Member

    Messages:
    145
    south london
    Thanks guys.

    I don't want to use a longer cone as I don't want the final product to be longer than 40mm.

    What's erw? Yes I might have to use cds as I thought. It only needs stretching, there is no shrinking involved. The bottom end needs to stay the same, while the top is stretched.

    No point in cutting and welding as I'm trying for a production run. Kinda defeats the point if I can't do it quick and easy.
     
  6. WorkshopChris Forum Supporter

    Messages:
    3,141
    Location:
    South East Essex
    Electric Resistance Welded Tube (ERW) Seam welded.
    I would be surprised if you could produce the required profile just by stretching.
     
  7. pdg

    pdg Member

    Messages:
    10,496
    Location:
    Wiltshire
    I think you could stretch it, but not like you're trying...

    If you want to do it over a die like that, then something more progressive - like say 3 or 4 dies getting wider each time.

    Or, imagine a round split down the middle and driven onto a wedge (crappy drawing available on request).
     
  8. hooblah Member

    Messages:
    145
    south london
    I've spoken to someone who's done similar, he said he used s235jr tubing with a 2mm wall, no heat. Ive had a look but I can't seem to find any.
    I called my stock supplier who I got the last length off and he hasn't a clue what grade his is, "just normal mild steel mate!". Useless!

    Ive also looked into cds tubing but still can't find anything 42mm with 2mm wall .They're all 3mm+ :(

    Next job will be having a cone machined so I can flare it out. Anyone able to do that for me?
     
  9. johnser

    johnser Forum Supporter

    Messages:
    1,393
    Location:
    North Cornwall
    How about squashing the end so the two curves match the radius you want to achieve on your finished item, then slitting back a certain length and, with heat, pushing it onto your former.

    The infils you need can be easily cut from flat and welded in.
     
    ronan likes this.
  10. ronan

    ronan Member

    Messages:
    6,942
    dublin
    Thats what i would try.
     
  11. hooblah Member

    Messages:
    145
    south london
    Sounds like too much effort. I'd rather form it than have to cut and weld . It wouldn't work for a production run .
     
  12. graffian

    graffian Seer unto the end of his beard

    Messages:
    2,251
    surrey
    What's the circumference of the ovalish hole?
     
  13. daedalusminos Member

    Messages:
    207
    Location:
    Norwich
    Try heating and hammering the outside with the nose of an anvil inside - this should thin the wall a create a natural bell....then use your former
     
  14. 8ob

    8ob Member

    Messages:
    1,476
    Location:
    moscow on thames
    ronan likes this.
  15. hooblah Member

    Messages:
    145
    south london
    Don't know the circumference . I'll have a measure.

    No I'm not beating the wall to thin it. I need a professional looking final piece, not something that looks like Stevie Wonder made it. I don't have an anvil anyway.

    Nope I've never seen a ms concentric reducer, only stainless.
     
  16. Bladevane

    Bladevane Member

    Messages:
    194
    Location:
    Harwell, Oxon
    Ductility is the key here. I've seen 50mm OD x 6mm wall boiler tubes capable of withstanding 175 bar under tests similar to the shape you are requiring. Material was 16Mo3. IMG_2490.gif
     
  17. 8ob

    8ob Member

    Messages:
    1,476
    Location:
    moscow on thames
    Plenty of Bosal stockist in the UK, 2mm wall thickness steel reducers http://vi.raptor.ebaydesc.com/ws/eB...ategory=42905&pm=1&ds=0&t=1497437948000&ver=0

    Bob
     
  18. Tupers

    Tupers Member

    Messages:
    404
    Devon - England
    You need to either make a couple more smaller forms to slowly bring out the shape or just make it from one tube cut down the middle with a triangular section top and bottom.

    Personally I would go for the latter unless you move to using stainless and use a reducer that you can squash.
     
  19. hooblah Member

    Messages:
    145
    south london
    Bladevane - that sounds expensive!

    I'd rather make smaller forms tbh. Mainly so I can keep costs down. If I can knock them out for as cheap as possible I'll be able to sell a lot more .

    Ok so I don't know much about pressing out parts, how much smaller should the forms be? How would staging the dies stop it from cracking? I'm still stretching it to the same size so that doesn't make sense to me.

    Im going to try repeatedly heating and pressing it bit by bit next .I'll report back on how that goes.
     
  20. anto44 Member

    Messages:
    425
    Location:
    ireland
    Starting with a cone like 8ob said makes this a lot easier. The former in your pics is very rough as well, formers for stuff like that should be polished perfectly smooth to reduce friction and let the metal slide on the former rather than dragging on it
     
    WorkshopChris likes this.
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