Joint restraint cracking

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Alright, I work in a machine shop as a welder and part time machinist.  Quite frequently I get jobs, mostly repair jobs, that require a press/heat shrink fit along with welding.  Most times these welds are tig welds.  Problem I'm having is getting root bead cracks instantly when trying to join the two parts with the interference fit.I'm looking for solutions to fight this crack issue.  So far the only successful way I have been able do these is to give a heavy pre heat and maintain that elevated temp.  Works fine for some jobs but others, that much heat could be an issue.
Reply:Post a few pics of the problem please.The interaction of the weld with the way the parts are put together will probably end up being the cause.I don't have a lot of experience with this topic, but the pics will help the pros who deal with this more often.Dave J.Last edited by MinnesotaDave; 06-18-2013 at 12:26 AM.Dave J.Beware of false knowledge; it is more dangerous than ignorance. ~George Bernard Shaw~ Syncro 350Invertec v250-sThermal Arc 161 and 300MM210DialarcTried being normal once, didn't take....I think it was a Tuesday.
Reply:Are you pressing the part into a blind bottom hole or a hole with a shoulder that the part can bottom against.  This could be the same problem a socket welded fittings gives if the pipe is let bottom out before welding.   Sounds like two parts growing or shrinking at different rates. Pictures would help a lot in this case.Dan
Reply:Originally Posted by DanD78Are you pressing the part into a blind bottom hole or a hole with a shoulder that the part can bottom against.  This could be the same problem a socket welded fittings gives if the pipe is let bottom out before welding.   Sounds like two parts growing or shrinking at different rates. Pictures would help a lot in this case.Dan
Reply:It would also help a lot to know what the parent metal is, what filler and thickness you are using, what machine settings you are using etc.Lincoln precision TIG 275Millermatic 140 MIG
Reply:Good practice is to preheat anything over one inch thick.  Many shops I have worked in say 3/4 inch to eliminate arguments and discussions with staff and inspectors that drop by.  This rule is intended for low carbon steel.   The preheat does not have to be very high. Over 200 degrees F is fine.  Moisture fom the flame should not condense on the material.  Try to heat so that the heat concentration is not just at the weld.  You are trying to avoid a steep gradient of temperature between the weld and the parent metal.
Reply:Are you welding free machining steels? Whats good for the machine shop is not always good for the weld shop.
Reply:Not welding any free machining steel.  Material choice is across the board though.  Sometimes low carbon sometimes high, sometimes it's a guess.  Material thicknesses varies also.The one constant I can think of, as mentioned above, is something pressed onto a hole.  Yesterdays case was a blind hole thoughHere is a pictureBroken shaft, customer did not want a new one made for cost reasons.  The 2 halves were faced off then drilled and reamed for a pin.  I believe the pin was .5" or .625" dia. And knowing the machinist, he probably went with a .005-.007" interference. The pin was bottomed out in both halves leaving roughly a 3/32 gap.When I lit up on this part initially, it was still plenty warm from being heat shrunk together.  The first weld instantly cracked thru the middle.  The only way I was successful, was to apply a lot more pre heat and continuously weld till I was above that gap.  I have had a couple other instances where this happens and it's not a blind hole.  Just a shaft pressed into a hole
Reply:It's the bottoming out of the material that is causing your cracks. Have them leave 1/16" gap on the inside of the hole. instead of seating it home.There are no problems. There are only solutions. It's your duty to determine the right one.Hobart Handler 210Airco 225 Amp MSM Stinger
Reply:I should have thought about that.  Going to bring that up with the machinist tomorrowWhat about the instances when it's not pressed into a blind hole?  Like a tube pressed in a plate.  Should I pre heat all interference fit joints
Reply:[quote=JRwldr;2777281]I should have thought about that.  Going to bring that up with the machinist tomorrowYes sulphurized and leaded steels create all kinds of welding problems.. often cracking as you mention. What about the instances when it's not pressed into a blind hole?  Like a tube pressed in a plate.  Should I pre heat all interference fit joints
Reply:It's always a good idea to do a spark test if you can to help get a better idea of what you're dealing with.In some cases you might be forced to use the really expensive nickel rods.Welding a bunch of short beads instead of one long one helps.  After each short weld, peen the hell out of it with a chipping hammer.  Chucke2009 on YouTube has some good videos about welding stuff that likes to crack.