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welding sheet metal - first attempt didn't go so well


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30 replies to this topic

#1 grossgary

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Posted 11 July 2012 - 07:57 AM

i have a basic box store wire feed mig welder. almost exclusively use it for exhaust and removing sheared/stuck/rusted fasteners.

welding sheet metal on a legacy fender did not go so well.

no matter what amps or feed rates i selected it would burn through the metal. i eventually got it to stick but it was ugly.

is the exhaust that much thicker, because i have no problems welding that?

#2 987687

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Posted 11 July 2012 - 08:22 AM

i have a basic box store wire feed mig welder. almost exclusively use it for exhaust and removing sheared/stuck/rusted fasteners.

welding sheet metal on a legacy fender did not go so well.

no matter what amps or feed rates i selected it would burn through the metal. i eventually got it to stick but it was ugly.

is the exhaust that much thicker, because i have no problems welding that?


Good chance the sheet metal is a bunch thinner. Also even if it's solid, but surface rust, sometimes it can have rusted thinner than you think. Making it a real bear to weld. I've run into that with exhaust, too.
And I learned all about trying to weld old sheet metal fixing up my GL.

If you hold the welder (whatever the handle thing is called), further away from the metal, it will make welding thin stuff easier. It makes more blobby bubbly welds because it's cooler. Since you have a longer stickout of wire, it cools off more before it gets to what you're welding.
This probably isn't proper, but it works, and with some practice, you can actually weld pretty thin stuff and have it come out looking pretty good.

I too just have a crappy cheap box that only has a couple heat settings, so every little trick helps out.

#3 grossgary

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Posted 11 July 2012 - 08:54 AM

cool, i've never intentionally varied the distance much like that, i'll try that next time. thanks!

had to do that on hard to reach stuff before and recall what you're saying.

#4 Turbone

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Posted 11 July 2012 - 09:19 AM

Are you using gas? Makes a big difference. Also make sure the surface is clean bare metal. When welding thin metal you need to make small spot welds, otherwise you burn thru and/or warp the metal. Spread out the spot welds then fill in after it cools down.

#5 grossgary

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Posted 11 July 2012 - 09:41 AM

Are you using gas?

no, it was the low end model that doesn't have gas adapters.

When welding thin metal you need to make small spot welds, otherwise you burn thru and/or warp the metal. Spread out the spot welds then fill in after it cools down.

copy that, will try that too. thanks rob.

#6 Reza

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Posted 12 July 2012 - 12:09 AM

Are you welding beads or spot welding it together?

Don't weld beads, just stitch it with spots. then use an air gun to cool each spot weld.

#7 Mugs

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Posted 12 July 2012 - 11:33 PM

Also your "cheap" version of what ever welder probably came with .030 or .035 FCAW wire. You need to scale back to .023 or .020 FCAW wire. Also as stated before, stitch don't seam weld. But if you do seam weld in a few places, push rather the pull the whip. This method does not penetrate as hard, and welds cooler, yet leave clean welds, that don't wrap the metal.

And of course I might add...you get what you pay for. So if you bought a cheap welder you'll get cheap welds. When it comes to this type of stuff its best to step up, but I understand the money thing as well. But look at it this way, sure it may hurt the pocket book now, but are you gonna notice the pain in a year...probably not.

#8 GeneralDisorder

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Posted 13 July 2012 - 05:04 PM

For sheet metal you really need thin wire and shielding gas. The flux will make it impossible to do short tack welds as the slag needs to be removed before striking the arc to prevent slag inclusion in your welds.

You don't actually have a "MIG" welder - common misconception. You have a "wire feed" welder, or FCAW (Flux Core Arc Welding). MIG stands for Metal Inert Gas welding and if the machine isn't capable of using gas then it's technically not a MIG welder at all.

Without a true MIG setup, .023 wire, and sheilding gas (preferably 100% CO2 as it runs colder) you are better off with pop rivets and aluminium sheet. FCAW for automotive sheet metal work is really difficult even for those of us that have some welding skills.

GD

#9 grossgary

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Posted 14 July 2012 - 01:27 AM

copy all, thanks guys.

#10 bratman18

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Posted 14 July 2012 - 10:02 AM

I have done many sheet metal patches with my cheap flux core welder. It takes a lot of practice to make it work. But once you get the hang of it, it's not too bad to do. Short pulses of the trigger works well. Always check for penetration, and strength to make sure your welds are good. They may not always look the prettiest, but you can smooth them over, and then use body filler to make it look good after. I have done a few rear quarter patches now this way, and they are still holding up well to this day.

#11 987687

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Posted 15 July 2012 - 08:45 PM

I have done many sheet metal patches with my cheap flux core welder. It takes a lot of practice to make it work. But once you get the hang of it, it's not too bad to do. Short pulses of the trigger works well. Always check for penetration, and strength to make sure your welds are good. They may not always look the prettiest, but you can smooth them over, and then use body filler to make it look good after. I have done a few rear quarter patches now this way, and they are still holding up well to this day.


I'll second this, I have a cheap fcaw. Sometimes my welds are a little boogery. But I can run a constant buggery bead between two bits of sheet metal and not have any pinholes. It depends on the quality you're looking for. If you're fixing up your beater GL, it's more than fine. If you're fixing a smashed panel on a brand new STi, ya, it's worth buying the good welder to make it come out well.

#12 mountaingoatgruff

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Posted 21 July 2012 - 07:36 PM

[quote name='987687']If you hold the welder (whatever the handle thing is called), further away from the metal, it will make welding thin stuff easier. It makes more blobby bubbly welds because it's cooler. Since you have a longer stickout of wire, it cools off more before it gets to what you're welding.
This probably isn't proper, but it works, and with some practice, you can actually weld pretty thin stuff and have it come out looking pretty good.QUOTE]

You're talking about electrode extension, or wire stickout. Longer stickout requires higher voltage to push the same current through the relatively small electrode used in wirefeed welding, hence more heat, not less. You need to tune voltage and wire feed speed/current together to make the arc length as short as possible and maintain proper stickout to limit heat input, not just pull the gun back.

#13 mountaingoatgruff

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Posted 21 July 2012 - 08:07 PM

For sheet metal you really need thin wire and shielding gas. The flux will make it impossible to do short tack welds as the slag needs to be removed before striking the arc to prevent slag inclusion in your welds.


Slag removal is tedious, not impossible. An angle grinder with wire wheel makes it easy if you can lay uniform beads. If you can't lay a relatively uniform bead chances are you can't recognize cold lap and shouldn't be welding on a motor vehicle in the first place, in which case more practice and technical understanding is needed.

You don't actually have a "MIG" welder - common misconception. You have a "wire feed" welder, or FCAW (Flux Core Arc Welding). MIG stands for Metal Inert Gas welding and if the machine isn't capable of using gas then it's technically not a MIG welder at all.

Without a true MIG setup, .023 wire, and sheilding gas (preferably 100% CO2 as it runs colder) you are better off with pop rivets and aluminium sheet. FCAW for automotive sheet metal work is really difficult even for those of us that have some welding skills.

GD


There's no such thing as true MIG with 100% CO2. CO2 is reactive, not inert. That's why the AWS designation was changed from Metal Inert Gas to Gas Metal Arc Welding, to include solid wire/reactive gas combinations.

Also, an argon rich shielding gas will run "cooler" and have less penetration and less spatter than 100% CO2. Depending on other variables, you will likely have more puddle control with an argon-rich gas, a big deal for hobby welders attempting out of position welds. C25 (75% argon, 25% CO2) is most popular for hobby welding.

I use GMAW with .023 wire and C25 gas for thin sheet. Flux core is a nightmare on thin sheet as the process is simply not designed for that application.

It should also be mentioned that you need clean, bare metal to weld. Welding over paint, rust or oil can contaminate the weld, cause critical defects and make control impossible because the arc is erratic.

Edited by mountaingoatgruff, 21 July 2012 - 08:11 PM.


#14 987687

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Posted 21 July 2012 - 09:02 PM

You're talking about electrode extension, or wire stickout. Longer stickout requires higher voltage to push the same current through the relatively small electrode used in wirefeed welding, hence more heat, not less. You need to tune voltage and wire feed speed/current together to make the arc length as short as possible and maintain proper stickout to limit heat input, not just pull the gun back.

While I understand that's how it works with a quality machine that has low enough settings, that's not what we're talking about here. A basic 110v machine actually doesn't often go low enough to easily weld sheet metal. It doesn't help that flux core wire is quite a bit thicker than solid core with gas, so we have to make due with what we have, and find "hacks" if you will, to make it work.

#15 mountaingoatgruff

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Posted 22 July 2012 - 12:00 AM

While I understand that's how it works with a quality machine that has low enough settings, that's not what we're talking about here. A basic 110v machine actually doesn't often go low enough to easily weld sheet metal. It doesn't help that flux core wire is quite a bit thicker than solid core with gas, so we have to make due with what we have, and find "hacks" if you will, to make it work.


All welding machines operate on the same principles of electricity. With wirefeed processes, the electrode is not large enough to carry welding current very far without overheating because it's small diameter creates too much resistance. A longer stickout means more resistance, which ultimately means more heat. The idea that longer stickout allows the wire to cool more is unfounded - the wire doesn't come out heated, its heated by the arc. Stickout is one of many variables a skilled welder uses to control the weld.

I don't think I've ever seen a 110V wirefeed machine that won't run below a 220V. Sheet metal is about the only thing a 110V GMAW machine is preferable for IMO.

For the most part, FCAW-S wires are available in the same sizes as solid core wires down to .030 while solid wire goes down to .023 that I've seen. The difference between an .023 and an .030 wire can easily be overcome with practice. Its the differences in the processes that make FCAW such a turd for sheetmetal.

Edited by mountaingoatgruff, 22 July 2012 - 12:11 AM.


#16 djellum

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Posted 23 July 2012 - 02:44 AM

the best general setup I can think of is small .020, .023 hard wire with 100% argon. you get a clean weld with 75/25 as well and its a bit cheaper. each area you take out of spec makes it a little worse to work with.

flux core is generally a higher penetration process than hardwire, and combined with the hassle of the flux its really a bear to work with on thin stuff.

any gas with helium, hydrogen, or oxygen (including CO2) will increase the heat. inert gasses like argon and nitrogen will not add heat.

a couple of thing that will help greatly...

metal prep. much of what you can accomplish is dependent on the shape of the metal. also be as clean as you can and take everything down to bare metal if you can.

if you want to weld thicker stuff than your welder can do in one pass bevel it ( |/ ) so you can get to the bottom.

a couple of things to help weld thin stuff is J grooves. make a small L at the end of each piece and clamp them together (looks like 2 J's in a mirror image). either weld down the little fence you just made or weld the groove on the other side. effectively gives you more material to absorb the heat.

you could also fold the edge, doubling the thickness of the piece you are welding in, just keep the gun pointed mostly at the thicker piece and just wash up on the thinner one.

You can sometimes switch the polarity. its generally not good since the wire and process are set up to do something specific, but 70-80% of the heat is on the positive side of the arc. if your workpiece is the positive terminal then you can switch it. just be careful, not all machines can do that, and the wire and gun will be getting really hot. don't ruin your machine.

another trick to try on some scrap. get a piece of copper from and old pipe or something and hammer it flat. Copper conducts well, so it won't mess up the arc and draws lots of heat away, but it has an extremely high melting temp. place i behind the joint you are welding and clamp it tight. its very possible that your machine won't be able to melt it so you can weld on top of it using it as a heat sink and it won't stick. lots of variables with it, but I have heard it works well in a pinch. you will prob have to go slow and/or cool it off often.

#17 grossgary

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Posted 23 July 2012 - 07:47 AM

still following, thanks all.

the technical stuff is way beyond what i have time for. wish i did, but i don't and won't. so for now i'll just be hack welding rusted stuff that has some more years left but doesn't need to look great.

#18 GeneralDisorder

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Posted 25 July 2012 - 12:23 PM

I was thinking of the wrong gas when I said CO2. I forget that my TIG uses 100% argon because of it's inertness and thus it's the one that would run colder.

So yeah - .023 and Argon is what you want for sheet metal....:-p

GD

#19 tallwelder81

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Posted 25 July 2012 - 02:49 PM

youre not using gas, and it doesnt even HAVE gas option?
let me guess, Harbor Freight? yuck...

if there is a way you can just weld flux-core, use that instead.
the wire costs a lot more, like 70 bucks for .032 10lb spool.
but it has the shielding gas contained within the wire itself.


also, dont try to weld from point A to point D. gotta space it out.
just go like a quarter inch, skip an inch, weld a quarter inch, skip an inch.

have a glass of water, smoke a cigarette, pick your nose, or whatever,
for like 2 or 3 minutes, then start back up. quarter inch weld, skip an inch, etc....

like this: --- --- --- ---

even with a 1,200 dollar lincoln electric pro model, skipping around is just part of working with that thin material.
think of it like the lug nuts on a big truck. you cant just tighten lugs on a 10-lug wheel clockwise. itr will jam and bind up and go on crooked.
you gotta do like bolt 1, bolt 6, bolt 3, bolt 8, so on and so forth.
if all else fails, solder then project.
i understand that we cant all go out and buy top-end tools for our home projects. but for the hundredth time, harbor freight garbage isnt even worth the price. if you want a cheap hobby welder, get at least an Eastwood. they are much cheaper than pro-stuff, but still work pretty good.
cheap tools cost more than good tools.
how about your time and gas? and the headache of dropping what you are doing, and running down to the cheapo china-mart toolstore to RE-buy the same tool, again and again?
dont think IM rich. i live in a 32 year old mobile home with a leaking roof. my garage is 2 shipping containers with pond-liner roofing and lumber from an abandoned trailer park that the county took over. i have literally not had any cable TV in over 2 years. my tv is nice, but its a 27inch from 2004 that i scored at a after-thanksgiving sale. and the newest video game system ive ever owned is an xbox. like, the FIRST xbox. i play call of duty 1, when i need a gamer fix.
but all that being said, i still either shell out big bucks for GOOD brand tools, or i live without them. if the cheap version is honestly good enough for you, chances are, you dont even need the tool anyhow.
theres my rant.

#20 tallwelder81

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Posted 25 July 2012 - 02:58 PM

wow, im dumb. i didnt get to page 2 of the thread. i just replied. lol...

anyhow, what i said was true. and i use the same .032 wire for everything. it worked okay on my battery tray, which i would guess is like 20gauge sheet.
and it worked good on the walls of a shipping container also, which is, i know for sure, 14g sheet. ive used it on 1/8" angle iron and box tubing also. none of the welds have broken yet on the 20g, 14g or 1/8". and the 14g and 1/8" weld beads look very pretty, as clean and steady as anything the college teacher showed me on mig or fluxcore/innershield.

if you REALLY want to weld a lot of thin stuff, and strong and clean, and do it all in shorts and a t-shirt, go spend a months paycheck on a nice Tig welder. the invertecs are very nice. i dont own one, but ive used em a LOT. no complaints yet. and for the power they put out, they are very portable.

p.s. am i the only one who thinks USMB should have a seperate section JUST for specifically metal fabrication?
i notice there are a ton of threads on here, just about working with metal. and metal related tools and equipment.

#21 grossgary

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Posted 25 July 2012 - 06:45 PM

very close - cheap Lowe's Chinese Special, LOL. i generally avoid body work at all costs. i just wanted to try this once and it didn't need to look good on this car. the lumpy excuse for welding that's the same color or if i would have riveted in a piece of metal instead...it all looked better than the huge honking rust hole that was there.

i totally hear you - better equipment is the answer. if i had time i would.

on my battery tray, which i would guess is like 20gauge sheet.
and it worked good on the walls of a shipping container also, which is, i know for sure, 14g sheet. ive used it on 1/8" angle iron and box tubing also. none of the welds have broken yet on the 20g, 14g or 1/8". and the 14g and 1/8" weld beads

it works fine for everything else - even thin exhaust and other small things, tiny nuts, plate metal, bolts, weld just fine. it's only body metal i have a problem with.

what's the thickness difference between exhaust and fender metal?

#22 tallwelder81

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Posted 26 July 2012 - 12:42 AM

maybe its not quantity, maybe its quality.
exhaust and nuts/bolts are generally a much higher quality steel than 80s fenders. especially NEW cars, like late 90s up til 2012. the steel is CRAP!

if 50s and 60s cars were made the same thickness as a modern car, they would still be far better quality, simply because the actual metal was better metal.

speaking of welding, did you know a LOT of the welding rod is old hondas and toyotas? true fact. they make 6010 and 6012 rod out of old 80s cars that got crushed.

#23 mountaingoatgruff

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Posted 26 July 2012 - 09:00 PM

Even if you have a cheapo machine I'd still recommend brand name wire. With cheapo stuff you often don't get specs and when they are available they're questionable at best. AWS doesn't verify electrodes meet standards, the manufacturer just claims their electrode will perform according to AWS classification.

Lincoln lists NR-211 FCAW-S wire for sheetmetal or structural fab up to 5/16" thick and for use in all positions. If you insist on running flux-core on sheet metal I'd use .030" NR-211.

Almost all flux-core wires are low hydrogen and need to be protected from moisture. Flux-core wire that has been exposed to moisture for a long time can go bad. Rusty wire is garbage.

Obviously, some wires have limitations like a max thickness or use only in certain positions. Its good to buy an electrode from a company that can reliably tell you how to run it otherwise you could be squirting bird poo simply because you don't know the operating parameters.

Lincoln's Innershield (flux-core) welding guide:

http://www.lincolnel...1-MP/c32400.pdf

#24 djellum

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Posted 28 July 2012 - 12:35 AM

are you pushing or dragging? what I mean is what way is the gun pointing while your traveling?

draggin, or keeping the gun pointed towards the weld you just put in will increase the buildup of the metal, and lower the penetration since the heat is being put into the area that is already thicker due to welding.

pushing or pointing the gun to the gap you haven't welded yet will increase penetration since your preheating the base metal a bit and reduce weld buildup.

for thin sheet you won't be doing much welding in a row like was said earlier. just get a dot on the edges about an inch or 2 apart. but don't do it in a row like was said earlier, the shrinking will pull the piece out of alignment that way.

if you want to put in more at a time drag the wire.

#25 djellum

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Posted 28 July 2012 - 12:39 AM

another thing I haven't thought about is ground. if you haven't been, make sure that both pieces are grounded. if the patch piece is gapped a bit where your going to weld it, it might affect the arc.

kind of a long shot, but might help.




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