Automotive Failure Analysis
Automotive Failure Analysis
(OP)
Hello all. I have been making custom transmission mainshafts for an adaptor I have been having them inertia welded. Recently one of the shafts failed. Obviously Im looking to prevent this from happening in the future and would welcome any analysis on the mode of failure as well as steps I could take to rectify this potential weakness.





RE: Automotive Failure Analysis
Where is the weld you mentioned in that picture? What is it made from, what conditions did it operate at and how long did it last..! Looks a right mess!
RE: Automotive Failure Analysis
When you say inertia weld, is that like a friction weld where a rotating and a stationary piece are joined together? Please confirm the joining process.
If so, I would suggest that the fracture be examined by a Metallurgist. There may be oxides in the fusion zone that were not purged during the upsetting step. The met exam can also provide hardness and microstructure.
Also let us know if the shaft was mechanically straightened after welding.
RE: Automotive Failure Analysis
dbooker -The shaft was friction/inertia welded and your description of the process is accurate. Thanks for the tips, I will inquire about those steps and see if those could be an issue.
Thanks for all of your help and suggestions.
RE: Automotive Failure Analysis
Gold is for the mistress - silver for the maid
Copper for the craftsman cunning in his trade.
"Good!" said the Baron, sitting in his hall
But iron - cold iron is the master of them all.
Rudyard Kipling
RE: Automotive Failure Analysis
-Thanks
-Ike
RE: Automotive Failure Analysis
Also, can you tell us whether the shaft is heat treated after friction welding, if so to what hardness, and what type of finishing was performed - grinding, hard turning, phosphating, etc. Anything you can provide will help.
RE: Automotive Failure Analysis
RE: Automotive Failure Analysis
RE: Automotive Failure Analysis
Friction welding is a non-fusion welding process. It is technically impossible to achieve 100% fusion if you, technically, aren't fusing the material.
[/Minor nit-pick]
But, yes, you should achieve complete bonding with a friction weld. It if obvious that the failed part was fabricated with a partial penetration fusion weld. Based on the apparent porsity visible, I'd guess FCAW, but could be SMAW or GMAW. Obviously, the weld was not up to the task.
If a friction weld isn't avialable, I'd recommend a TIG weld, with a filler metal to match the base material and a PWHT if needed to bring the HAZ back down to the base materal hardness. You'd also want to locate the weld at least 1/2" away from the end of the splines to keep the stress concentration from the splines away from the weld.
rp
RE: Automotive Failure Analysis
Be real interesting to see the results of a microhardness traverse along the shaft, including areas beyond the weld area in both directions. What is the shaft alloy and hardness?
Gold is for the mistress - silver for the maid
Copper for the craftsman cunning in his trade.
"Good!" said the Baron, sitting in his hall
But iron - cold iron is the master of them all.
Rudyard Kipling
RE: Automotive Failure Analysis
We had a rash of shaft failures immediately above a spline very similar to your photo, turned out to be field guys turning the air pressure up 2X the recommended.