There is a school of though that suggest stitch welding may be superior to seam welding for certain applications. If a crack starts in a stitch weld it will break through one stitch and then stop, providing a good visual cue to the operator/maintainer, and easy access for repair. If a seam weld cracks or un-zips it can propagate a large distance before it is detected and may be more difficult to properly repair.
What makes seam weld cracks harder to repair is guessing where to drill the stop-hole for the crack, because a crack will propagate further than is visually detectable. Of course X-ray or magnaflux (and other technologies) can help, but that's a whole other level from FRC. With a broken stitch weld the whole stitch can be cut and re-welded (if not already broken) with no need for a stop hole.
I'm going to stop myself here on the 'seam vs stitch' discussion unless there is a debate or questions that arise.
Quote:
Originally Posted by Rivet Man
Hi Spark,
Going to pretend I'm Weld Man here for a second...but if you're talking about bending the metal, a continuous weld is always going to produce more warping in a part than riveting if all else is equal.
Mainly what happens is you heat up the metal and it gets softer (more malleable, and a bunch of other science jargon). So what happens is it'll distort and actually pull to a side. Afterwards there will be additional stresses inside the material (as with all fastening systems, that's how they work) that keep the material bent out of place.
Even if you preset your material and had it exactly in place, a long continuous weld is 100% going to distort a thin sheet of aluminum. Fortunately, rivets have your back and could be used to hold the sheet in place to help reduce warping.
Here's a link that has some good tips on how to mitigate these warps.
http://weldingdesign.com/archive/avo...ion-thin-sheet
Main points from this link are things like, backward walking, non-continuous/stitch welding, and presetting.
It's true that rivets can bend a thin piece of aluminum, but that would mean you have other issues in your setup. If your pieces aren't mated correctly (air gaps, bends aren't proper) when you're about to rivet then yes, rivets will bend your rig...they're trying to pull the pieces together after all! And if we're talking about the retaining mandrel or the head impinging on the surface of the metal...chances are you're using too much force on too soft a material, that ones on you and not the rivet!
Rivets are only as good as the person/design that's using them, and they're definitely not the bad guy!
Best Regards,
RM |
To put some 'science jargon' there...
The metal will change shape due to extreme localized heating of the weld pool driving thermal growth of the material. Any softening is secondary this CTE (coefficient of thermal expansion) driven growth.
Warping can be managed by proper design, small or non-existent root gaps, fixtures, and sufficient tack-welding prior to seam welding. If a part comes out warped there are many ways to correct it that include bending, re-heating welds (sometimes with fixtures), cutting, stress-relieving (sometimes with fixtures), or any combination of the above.