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Old 11-02-2010, 12:35 AM
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welding...metal is brittle....any idea why?

B..een welding up the pin holes on my dart's roof at the roof rail. Drilled the spot welds to get the donor roof off. Used a 5/16 spot weld bit to get it done......2 people put my roof on at the factory. One was sober and made perfect welds.......the other was drunk and decided to drag the spot welder making long welds.......in drilling these drunk welds out I got very close to the rail and someimes even into the rail. This left no flat area to reweld the roof back on to the car.

I built the metal up some but when I gound it back down to shape it it cracked because weld with the mig is brittle and sheetmetal isn't work hardened.

How can I get these flat spots back to weld to the roof without it being brittle......I'm using a lincoln mig 140 with wire speed 3 and heat on setting c. Can I reverse the brittle effect of the mig. Maybe by anealing
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Old 11-02-2010, 04:07 AM
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Maybe some pics would help...
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Old 11-02-2010, 06:14 AM
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close to the roof rail. this spot is now built up with mig weld. if its hard to see .....there is a 90 degree angle there at that crease
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Old 11-02-2010, 07:16 AM
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Since you've done all this work ,I'd say you could handle making a patch or small patches for those tear outs insted of filling with weld,for one thing your taking a big chance on warping the whole roof with all that welding and you'll still have to make a hole to plug weld it back on....since it has rust pin holes sometimes the whole section should rereplaced.Look at the back side to see how bad it is....test the strengh of the steel around the holes with a pick hammer where the pick goes through it'll make a little volcano ,grind that flat to the surface and use a copper backing plate to weld the holes ,its much easier and does a nicer job.same with welding patches ,use some copper as a backing plate when welding up your butt seams dont try to do one continuous weld bead ,just one spot weld at a time and let cool.
Hows the inner structure look as far as rust goes...That'll need a good cleaning before you start welding the skin back on...You can use your old skin for making patches if it has any good spots...
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Old 11-02-2010, 05:34 PM
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Everything is welded shut. The pin holes are mostly gone. You see in the pic how that large hole covers the horizontal and vertical part......the verticle part is the roof rail and has nothing to weld to. Only the flat part gets welded where the spot welds were. Since it was very structured here it didn't warp. But these fill welds are brittle. How can I keep them from work ahrdening.
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Old 11-03-2010, 05:33 AM
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If I understand you right you cant.the weld is always harder than the soft steel of roof. If its cracking on the edges of the weld ,weld the cracks.
the heat settings on that a little welder may be a little low. a cold weld will also crack like that..Then again so would to much heat...would you like me to explain how I set the heat and wire speed just right? I'm pretty sure those 140's use both gas or flux wire,your using gas ,right?
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Old 11-03-2010, 10:30 AM
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Wire feed settings

Dbm,Sure go for it.I for one am always interested in finding the easy way!
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Old 11-03-2010, 10:44 AM
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The EZ way ........to set the wire speed and heat????
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Old 11-03-2010, 10:59 AM
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Quote:
Originally Posted by deadbodyman
The EZ way ........to set the wire speed and heat????
Don't know if it is the EZ way but would like to hear/read your method.
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Old 11-03-2010, 12:47 PM
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Heres how I do it .I dont have any pics of what it looks like so I'll do my best.
using a scrap piece of similar metal,in this case the old roof. pick any heat setting lets say 3 set the nozzel on the work and without looking,pull the trigger and starting with the wire speed low (say 2)turn the speed up until it sounds something like an egg frying then repete again in a fresh spot ,welding one spot and not moving,look at the weld ,If its a piled up it needs to go hotter if it burns through it needs to be cooler.keep doing it untill you get a weld as close to the surface as you can get it without burning through (like a pancake)....every time you change your heat setting the wire speed needs an adjustment too it should always sound like eggs frying .....good welds need little grinding...when you weld in a patch just weld one spot at a time and let it cool you alternate your welded spots like you torque a head...When you do a butt weld with sheet metal you need lots of heat and one short flick of the trigger ,the weld should be all the way through to the other side and you have good penitration ,it shouldnt look like a BB stuck between two pieces of steel...believe it or not you'll get a lot less warpage with higher heat and a short burst of the trigger than you will with heat setting not high enough...the last small welder I used was a miller 110 and I had to have it cranked up to 6 or 7 to get it to weld right ,they're all different...My big 220 welder is set around 4 for an idea how different they are ,both used 030 wire...wire size changes everything too. every time I try to weld without setting it up first I have trouble so I always set it up with a piece of scrap and everything works out great...Its ez to remember "fryed eggs" for the wire speed...pancakes for the heat...no muffins please....I sure hope this helps someone ,its how I was taught and it's served me well teaching my help over the years but its alot easier to show someone than write about it...I'm sure someone else would have some pics and a better explaination.
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Old 11-03-2010, 02:19 PM
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Wow bro, that was a thorough tutorial. I think I lernt sumpin from you.
Thanks,
Chip.
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Old 11-04-2010, 05:00 AM
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Thanks DBM. Will try that soon.
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Old 11-04-2010, 07:06 AM
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Quote:
Originally Posted by cyclopsblown34
Wow bro, that was a thorough tutorial. I think I lernt sumpin from you.
Thanks,
Chip.
Thank you ,Thank you very much,.... just dont ask me to teach you how to dance ...All I can say is, do all your welding with flip flops on and learn the hard way ,like I did...
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