Advice Needed with shearing occuring adjacent to weld

[duffman1278]

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.

 

[duffman1278]

Thanks for that link Mint!

 

[duffman1278]

Sprocket used on this design is 250mm though :/

 

[Guest102023]

Start at the beginning and request a lab to determine the crack mechanism. If it is at the weld toe (and corrosion is not a factor) then there are really only two possibilities for carbon steel: hydrogen cracking shortly after welding; or fatigue cracking after some time in service. These mechanisms are quite easy to differentiate. So your first important clue will be the answer to "where was the part when the crack was noticed and when?"

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.

 

[msquared48]

In comparing the picture to the drawing, the two don't seem to be the same situation to me.

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

 

[stanweld]

duffman1278,
Methinks that you will simply transfer the fatigue failue to the redesigned welds - assuming original failures were fatigue related.

 

[duffman1278]

I thought I mentioned in the OP that the picture wasn't exactly what I was working with but a similar concept. Guess I should have mentioned that =] We'll see how this turns out during the life test.