Prevent Shaft Bending

I would have thought a telephone call to the alternator manufacturer's technical helpdesk would have been a worthwhile first step, Guvnor.

Even application of heat while welding is the only way to minimize shaft warpage.

The same amount of heat must be applied to opposite sides of the shaft when welding, or the entire shaft must be preheated and small beads applied alternately to opposing sides.

Consider the amount of thermal expansion caused during welding.

Lyn is providing spot on advice.

This is all about thermal expansion and contraction and the resulting stresses and deformation.

A couple more things that may help...

1.Using more precise process is a big advantage. TIG is a much better choice than stick or mig.

A good free standing or integrated pulser unit is very useful for minimizing distortion with proper technique. One method programing a pulse sequence of a very brief faily high current (sufficient for good penetration in that short time) followed by low current (but not low enough for arc instability) at a rate limited by either the equipment or by your eyes ability to clearly and accurately discern given the rapid flashing. The brief period the pool is molten, coupled with the small size of the momentarily molten pool (as compared to a continuously molten pool) can result in far less distortion and lower residual stress.

Multiple smaller passes are often better than very few but large passes.

Do a good job aligning the pieces and tacking the work together, but then remember to remove clamps and jigs restraining the free movement of the pieces being joined. It may seem counter intuitive but restrict movement in an attempt to reduce distortion will often result in severe distortion and high internal stresses.

Slow rate welding is the solution. little bending is not a problem because it can be corrected by turning at lathe. After fine lathe burnishing operation is must to get required journal surface quality (mirror finish cold work hardened surface).

'...Slow rate welding is the solution...'

I disagree with this statement as it runs counter to theory with which I am familiar and personal experience...

I am always open to having my understanding upgraded.... Could you please expound upon your suggestion and the reasoning behind it?

Maybe turning down the shaft and installing a sleeve would be better? No worries about warping.

Thank you.

I appreciate unbridled admiration.

Why not start your own forum, then you can make up the rules, too.

I've built up plenty of shafts for re-turning. For this gen, you are building up the bearing area, and a fan mounts outboard of this? The slightest warpage will throw the fan out of balance, shake the whole gen apart.

Like Lyn said, sleeve the shaft, or weld up the whole end and turn everything new.

It was always fun heating up a long sleeve, and having it shrink and seize up before getting all the way on....turn it off and try again, LOL.

I didn't mention, but when I built up the shaft ends by welding, the machinist would have to put the shaft in a steady rest and re-tool the center hole to be sure it was concentric with the rest of the shaft.

I would weld a line down the shaft, rotate 180 degrees and weld a line, rotate 180 degrees and weld a line, rotate 180 degrees and weld, etc. until the shaft was all welded. This kept the warp down some, but hot metal always warps.

you dont weld such a shaft . use high velocity metal spray and machine that back as it wont put heat into the shaft.

there should be many coating systems people around you , they can do it with flamecoat , plasma spray , high velocity ionised metal , ceramics , you name it.

by the way . never put a sleeve on to a shaft thats carrying high loads , the metal WILL stretch and come loose on the shaft

i have seen many people try and fail , even if using high tensile steel and making it a shrink fit - forget it.

If your bearing is a ball or roller type, you can also opt for an off -size smaller hole bearing.

Now a days electron beam welding is being done over the turbine rotor's bearing areas for size reclaimation. This is just like conventional welding but the very thin filler wire is used and electron beam is used as power source. Heat input is very very small and thus chances of bending are negligible. MAN-TURBO is doing this type of repair.

my machinist done the job this morning by weld a small beads then air blow the shaft the heat didn't penetrate into the center. He is very confident because a few seconds later the shaft can be hold by hand its not really hot. He turn the shaft 180 deg. then weld again, then turn again 180 deg.

by the way thanks to all ideas posted here.

dar76

Good show!

Running a test weld on scrap pieces of metal that matches the metal that will receive the final weld will help you determine the best method for controlling heat distortion.