which is stronger

huangyhg

which is stronger?
when building a structure from tubular material, would the use of bends in continuous piece be stronger and more rigid than the same angle being made out of two straight pieces welded together? assuming a good mandrel bend(outside radius stretched, inside radius commpressed)opposed to a large radius weld. the material is 4130 .083 thick.-thanks
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generally it is felt better to bend the metal than to weld it although there is no difference in strength. firstly it is cheaper as you take most of the labour out of the process, secondly, welding the material may cause problems in producing permanent deformation in the beam due to the weld stresses, and thirdly, a weld is more likely to fail due to fatigue for the same stresses than plain material, if varying loads are to be encountered. the problem with bending the material is that it may crack, however, and you would have to choose the material carefully.
umm
bending: cold working adds strength
welding: welds often are not perfect
the thichness limits bend radius
bending can also distort the cross-section...
that is why there are limit on the bend radius.
jstein..considering the thickness you are dealing with and the difficulty in achieving consistent weld quality on thin materials, i would opt for bending.  if this is a fracture critical or fatigue sensitive application, even more reason to go with bending.
thanks! as you probably know this a race car roll cage.there is no post heat treating after the welding is done. knowing this ,would the structure be stronger with the pieces welded one on top of another(like limbs to a tree trunk) or welded slightly apart from each other(so that the welds don't overlap)thanks again!
thin wall tubing normally does not require stress relief. for parts thicker than .120", stress-relieving is recommended and 1,100&ordm;f is the optimum temperature for tubing applications.  weld rod er80s-d2, should be used. this filler material is capable of producing welds that approximate the strength of 4130.  thin wall tubing (< 0.120" wall) applications do not typically require the normal 300&ordm;f to 400&ordm;f pre-heat to obtain acceptable results. however, tubing should be at room temperature (70&ordm;f) or above before welding.
the two options should be considered for a design and fabrication veiw point since the there is little difference in the weld strenght.