Fixing a crack in steel
Fixing a crack in steel
(OP)
I have the arm from an eliptical. it has a thin crack starting on the upper arm (see attached). I was thinking of mig welding this? would that make sense? do I have to prep the surface at all? or pretty straight forward weld down the cracked area over the painted surface? the metal plate is about 1/4" thick steel and about 2.5" across x 1.5". Any settings on the mig welder I should use for this. Is this even a good way to fix this?





RE: Fixing a crack in steel
If you insist on doing it yourself, grind a Vee into the crack, making it about 90° open. For 0.035" c/s wire, a good setting is 200A and 22V. Which, unfortunately is too hot and too fast for an inexperienced welder -- please refrain from asking how I know so much about the limitations of inexperienced welders.
RE: Fixing a crack in steel
RE: Fixing a crack in steel
RE: Fixing a crack in steel
Grind the outside of the crack down to sound metal (about 1/2 the thickness of the base metal). Extend the excavation at least 1/2 inch beyond the visible crack tip. Weld the excavation from the outside.
You should now have a complete joint penetration weld that is as strong as the original member (assuming it is low/medium carbon steel). If necessary, grind the inside or outside as needed to fit flush with mating part.
Best regards - Al
RE: Fixing a crack in steel
RE: Fixing a crack in steel
RE: Fixing a crack in steel
If you are using MIG welding and are not sure of the machine settings to use, you should do a couple practice welds on some scrap material. Since this material is mild steel, MIG should work as well as TIG if performed properly.
RE: Fixing a crack in steel
RE: Fixing a crack in steel
RE: Fixing a crack in steel
Repairing this area will introduce further softening and failure will re-occur. If possible, I would replace the entire cracked bracket with a new one using the GTAW process. I would also stress relieve the new bracket after bending to ensure there is no metallurgical notch after welding because the bend radius is very close to the edge of the weld.
RE: Fixing a crack in steel
Farm Advice
Regards
StoneCold
RE: Fixing a crack in steel
At least then they are on notice that their machine is prone to breakage.
B.E.
You are judged not by what you know, but by what you can do.
RE: Fixing a crack in steel
As others noted, it looks like there is a flaw in the design of your arm. So it would be a good idea to add some local reinforcement when you are making the weld repair to prevent the problem from reoccurring. It would be very helpful if you could provide a photo of the arm bracket assembled with its mating parts and a more detailed description of how loads are applied. Or even better you could measure the parts and provide a dimensioned sketch of the bracket assembled with the mating components.
What you'll find with these forums is that the quality of feedback you receive will be proportional to the effort you put into your posts. Obviously in this case you simply initially sought some advice on making a weld repair to a cracked part of an exercise machine. You could probably have purchased a replacement part for about $75, which would have been the easiest way to resolve the problem. But since you are also an engineer, you may have seen this as an opportunity to develop new skills by making the weld repair yourself. So you (wisely) sought some advice from this forum on how to weld repair the crack. However, as engineers faced with resolving problems like this we're taught to address the underlying cause and not just the symptom. In your case the symptom is a crack in the bracket, but the underlying cause is likely the result of factors like insufficient material strength, manufacturing defects, design flaws, etc. So in order to fully evaluate the problem engineers naturally want to have as much information about the situation as possible.
Hopefully, as an engineer you will see this as a great opportunity to learn more about welding and also the engineering process used to evaluate problems and come up with corrective solutions. Or as StoneCold noted you could "just weld it up and use it until it breaks again."
Best regards,
Terry
RE: Fixing a crack in steel
(2) Getting back the part's dimensional integrity will be the bigger challenge.
(3) You need to investigate what kind of wrenching caused such a severe crack.
Apart from an unintended loading event, it looks like a design and/or manufacturing flaw (which I realize does not narrow it down very much). Hint: the crack nearly coincides with a sharp corner - was it precracked during forming?
"If you don't have time to do the job right the first time, when are you going to find time to repair it?"
RE: Fixing a crack in steel
A picture of the item installed would help - It might be better to replace the C shape with a 90 bend that lays along the side of the tube, a piece that can be thicker.
What does the piece on the other side look like - assuming the machine is symmetrical?