Advice Needed with shearing occuring adjacent to weld
Advice Needed with shearing occuring adjacent to weld
(OP)
I am investigating solutions for my company on a weld that they have had failures with in the past occurring next to the weld. In the picture below it doesn't show any cracks but I highlighted where the incident occurs at.
I'd appreciate some suggestions as to ways to prevent this because on an up coming product, the crank will be experiencing much greater torque than the sample part I have shown in the picture and so we'd like to avoid this. My only thought was to either preheat the parts before welding or post heat treatment? Both seem like slow process's that would hold up the mass production of these parts.
I would like to bolt down the hub that the sprocket mounts to (the picture shows a pulley but this is for a different product) however because of the limited space that we have to work with, it seems like we have no choice but to weld it.
I'd appreciate some suggestions as to ways to prevent this because on an up coming product, the crank will be experiencing much greater torque than the sample part I have shown in the picture and so we'd like to avoid this. My only thought was to either preheat the parts before welding or post heat treatment? Both seem like slow process's that would hold up the mass production of these parts.
I would like to bolt down the hub that the sprocket mounts to (the picture shows a pulley but this is for a different product) however because of the limited space that we have to work with, it seems like we have no choice but to weld it.





RE: Advice Needed with shearing occuring adjacent to weld
It's gonna break.
RE: Advice Needed with shearing occuring adjacent to weld
RE: Advice Needed with shearing occuring adjacent to weld
You also failed to mention whether the failures were due to fatigue or if they twisted (torque) and sheared or if the failures were at the toe of the fillet or in the HAZ or in the unaffected base metal.
Details my friend, we need details.
Best regards - Al
RE: Advice Needed with shearing occuring adjacent to weld
My mistake
RE: Advice Needed with shearing occuring adjacent to weld
I would expect fatigue cracks to initiate at the toe of the fillet weld. That is where the notch effect is the greatest and it is the location where you can expect to find minute oxides extending into the HAZ along the weld interface. While the shaft is rotating at relatively low rpm, it would not take long to accumulate 10 000 cycles, the point where a number of welding standards require the designer to consider fatigue. Small eccentricities or wobbles are all that is needed to initiate fatigue in the assembly.
One corrective step you could consider is to contour the weld after welding to produce a concave face and refuse the toes of the weld before contouring to melt out the oxides at the toe of the weld. Contouring would reduce the notch effect of the geometry at the toe of the fillet weld. Any undercut, regardless of how minute can be a significant stress riser when fatigue is a consideration.
I would also check the carbon equivalency to verify sufficient preheat is being used to prevent undesirable microstructures in the heat affected zone. I suggest you review Annex I of AWS D1.1 to determine the required preheat based on the chemistry of the shaft material.
You should also check the cleaning process used before the pulley is welded to the shaft. Cutting fluids used during machining or cutting operations are notorious for containing sulfur compounds and hydrocarbon. Both are bad actors when diffusible hydrogen is suspected of being a factor in weld failures.
Best regards - Al
RE: Advice Needed with shearing occuring adjacent to weld
RE: Advice Needed with shearing occuring adjacent to weld
Your image and comments indicate the cracks are likely to occur away from the actual weld. Is that right?
Do you have any pictures of both fracture surfaces of some failed shafts?
I'm guessing there are bearings on that shaft somewhere. Where do they sit, and how are they retained?
the scale of the part is hard to judge. I'm guessing the bolts are 1/2 inch or smaller. Is that right/
Is that a poly-v belt sheave/pulley?
RE: Advice Needed with shearing occuring adjacent to weld
If you can give us the shaft material, shaft diameter, your filler wire specifications and the welding parameters.
RE: Advice Needed with shearing occuring adjacent to weld
RE: Advice Needed with shearing occuring adjacent to weld
RE: Advice Needed with shearing occuring adjacent to weld
RE: Advice Needed with shearing occuring adjacent to weld
Most likely cracks due to cyclic stress. That type of connection is prone to it, and there should be relatively simple solution to someone with appropriate mechanical design knowledge.
RE: Advice Needed with shearing occuring adjacent to weld
I took the 'saw tooth part" to be a chain sprocket further along the shaft, >>perhaps<< at the end, with all the support bearings in the middle, but the assembly is sitting on the desk with a tilt as if a stub shaft extends beyond the pulley/sheave, so there might be a bearing seat there. Lots of missing details to be sure.
RE: Advice Needed with shearing occuring adjacent to weld
RE: Advice Needed with shearing occuring adjacent to weld
RE: Advice Needed with shearing occuring adjacent to weld
I wasn't able to get the composition of the material. The supplier is lagging or ignoring my emails.
RE: Advice Needed with shearing occuring adjacent to weld
And your weld symbols do not appear to conform to any standard.
What do you think the load path is?
RE: Advice Needed with shearing occuring adjacent to weld
RE: Advice Needed with shearing occuring adjacent to weld
Why waste the time and effort kludging something together?
RE: Advice Needed with shearing occuring adjacent to weld
RE: Advice Needed with shearing occuring adjacent to weld
RE: Advice Needed with shearing occuring adjacent to weld
The RPM of the shaft is irrelevant; eventually the part will accumulate hundreds of thousands of cycles or more, it will just require more calendar time to do so. IF it turns out to be fatigue in the shaft, I will tell you in advance that making the fillet weld bigger will not help. Misalignment will be the primary driver for fatigue.
RE: Advice Needed with shearing occuring adjacent to weld
In the picture, you indicate theat the failure is in the shaft near the weld of the shaft to the belt pulley. The sprocket in the picture is at the other end of the shaft from the weld.
In the drawing, the sprocket appears to be at, or near, the weld, and the weld is not to the shaft itself, but another part the shaft inserts into.
Personally, I am confused here.
Mike McCann
MMC Engineering
http://mmcengineering.tripod.com
RE: Advice Needed with shearing occuring adjacent to weld
Methinks that you will simply transfer the fatigue failue to the redesigned welds - assuming original failures were fatigue related.
RE: Advice Needed with shearing occuring adjacent to weld