WHAT IS THE PROPER WAY TO WELD PATCH PANELS WITH A MIG

[rockytopper R.I.P 5-13-2017]

I would like advise on welding in patch panels(BUTT WELDS) with a Mig. I have watched several videos on how to do it. I get the part about tacking the panel in first and working all around it to control heat. The part that seems to be different depending on who's instructions you follow is how to complete the welds. Some instruction vids say to keep spotting moving around the panel filling in next to a weld and continue until it is all sewn up. Other vids show having all the tacks about 1/2 inch spacing and then start at one end and weld next to the previous weld keeping it cool as you go and moving in one continues direction. What are your guys that do this thoughts on the subject. I have also seen hammering of the welds after each spot. Some instructions show doing this some do not. What is the advantage or disadvantage of not doing it. For the panel I'm going to have to work with you cannot get to the back side to hold any kind of dolly behind it for hammering.


Robert if you already have video instruction of this please share it.

Thanks
Rocky

[Rick_L]

Look at almost any of MP&C's how to posts. Basically you just keep tack welding until it's welded solid. You want to put enough heat in each tack weld so that it's a relatively low and flat dome rather than a ball. You may need to do some partial metal finishing once you are about to connect all the dots.

With mig, I usually don't do any planishing until I'm done welding unless there's some obvious distortion. Sometimes you need to make access so that you can planish.

[chevynut]

If you can't get to the backside you're going to have shrinkage and therefore warpage. So imagine that the entire weld bead is smaller than the surrounding metal, and you can kind of predict what will happen.

I fit the panel as close as I can, with no intended gaps. I don't like using the panel clamps that put a space between the sheets. Then I tack about ever 6" or so, then tack again between those tacks. Hammering the tacks slightly as you go is a good thing. I keep cutting the distance in half between tacks until I have about 1/2" gaps. Then I weld the gaps, jumping around the panel welding every 1-1 1/2". Keeping it cool is a good thing, but it's not going to prevent warpage.

20090317_1364.jpg 20090317_1372.jpg

[rockytopper R.I.P 5-13-2017]

Thanks guys that helps. I also found Roberts lesson on planishing.

http://www.bangshift.com/forum/forum/bangshift/tech-section/46064-planishing-mig-welds

so that helps me understand what it's about and why it's done. When I said I couldn't get to the back side I mean it ain't easy to access and I thought the welds had to be hammered when still hot. Which would be difficult to do. So basically I hammer as I go monitoring the panel effects along the way.
Rocky

[Rick_L]

Rocky, there's really no way to planish mig welds hot as you go. The reason for that is that mig adds too much filler to the joint. You have to dress the mig weld bead back to flat before you can planish it fully.

About a year ago I attended a class/demo presented by the old customizing wizard Gene Winfield on chopping tops. He, with the help of the class, chopped the top on a 41 Chevy coupe in about 20 hours (along with some demos and instruction that wasn't direct work on the car). 95% of the welding on the top chop was gas welding. The gas welds were planished hot by heating with a torch after the welding was complete. You can do the same with tig welds. I've done tig welds (mostly on the bench) with minimal or no filler metal that can be planished cold.

Just one more thing. I read about cars that Gene Winfield built when I was in junior high in the early 60s. Gene is still going strong, he's 87 years old now. He's fit and enthusiastic and a great guy. I was just amazed by him. The class was a lot of fun as well as instructive, and he interacted with everyone there.

The original idea about going to the class was just because it would be cool as well as a learning experience. And it was all that and more.

[MP&C]

Most patch panel installs involve a somewhat flat crown in both the horizontal and vertical directions. Regardless of appearance, all body panels will have crown in at least one direction to help hold the shape of that panel. A flat sheet of metal has no support and will flap in the breeze, so ALL panels will have crown somewhere. If we were to look at your top seam along the weld in a cross-section view (top-down) you would see that despite appearing flat, that panel actually has crown from front to back. It looks like a slight arc. Now, anytime you apply the heat from welding, you are going to get a shrink as that weld cools. When we weld one dot at a time, each and every dot is going to pull at the metal around it, from all directions, causing a shrink. Once you've added all those shrinks from all those weld dots together, along the entire weld seam, it adds up to a substantial amount of shrink such that what used to look like an arc is now more closely resembling a straight line. So given a weld seam like that, without any planishing to counteract the shrinking, you will see the panel pulling inward, as the crown at the weld is shrinking. Looking at the panel as a whole, unchecked shrinking would appear as a pronounced valley, where the weld seam is shrinking and pulling the adjacent panels along for the ride.

On the panel fitment, you will likely find that the sharp 90 degree corners on the patch will help to add a bit of distortion. As your welds shrink, a tight inside corner gets those effects from two different directions, where the shrinking effects will compound in the inside corner, normally as a pucker that is a bit challenging to remove. On the corners a large sweeping radius helps to balance out the shrinking effects on either side of the weld, where the planishing efforts don't need to focus on puckers or deformity on one side only.

As to addressing the welds:

I have found that due to the manner in which each weld dot shrink pulls from ALL directions, you will have better luck in planishing to remove said shrinking effects if you can planish the weld dots while they are singular, sitting all by their lonesome. This will more effectively STRETCH that weld dot back out in all directions. And by stretching as you go, you help eliminate the panel being pulled into a valley on those long welds. As far as tacking the panel in place, (FYI) I normally would start the tacks at one end and work toward the other. I know many people will tell you to skip around to minimize heat buildup, and I have been one of those. But if you tack one end and then move to the opposite end, you run a greater risk that one panel may have more material than the other due to misalignment. Once things get all tacked up, this results in a panel bulge on one side of the weld. So tacking from one end and working progressively to the other will help to eliminate this by being able to align the panels together as you go. Now that the panel is tacked and weld dots are spaced about (2 or 3"), go back and planish each weld dot individually, to add a bit of stretch. At this point, I use a 3" cutoff wheel to grind down the dots to just above flush. This gets them out of the way for planishing the next sets of dots, and by leaving them just above flush, you can do the final cleanup with a roloc sander all at once. By trying to grind things down to perfectly smooth after each, you run a greater risk of inadvertent sanding of the metal to the sides of the welds, which may thin and weaken the panel. So I hold off on this until the end. For your grinding disc, I prefer to use cutoff wheels about 1/16 thick. This gives a much smaller contact area than most any other method, so you will have less heat buildup from the grinding process. It also gives the best unobstructed view of what you're doing, so again, less chance of inadvertent abrading/thinning of the parent metal to the sides of the weld. Other grinding methods, such as using a flap disc, hide most of what you're doing, and generate too much heat. Here is a link showing the grinding method on a plug weld, again, sanding on a weld seam I would wait until the end.

https://www.youtube.com/watch?v=V2WHT_zMOE8

Once these initial welds are planished and ground down just above surface, then continue, adding a weld between each one until your welds are spaced about 1" apart. At this point (still planishing and grinding after each time) instead of hitting the center between for weld location, start overlapping by about 1/3 of the last welds. By overlapping, you will have less risk of missed spots or pin holes. Continue with the weld, planish, grind, repeat until the seam is done. I typically weld from start to finish using weld dots only, none of the longer passes at the end, in order to keep everything consistent throughout the process.

For the cutoff wheels, I spend the extra coin and get ones rated for stainless steel. This makes them last longer and put less of that brown haze in the air that you see from the cheap HF or swap meet specials. By the time you figure out the cost of how quickly the cheap ones wear away, you haven't saved a thing. For the roloc sanding disc, the bulk of the welds are being removed by a cutoff wheel, we are only dressing what little remains of the weld and blending that into the parent metal. This is easily accomplished using a 60 or 80 grit, that should be as coarse as you need to go..

WELD LOCATION!

There are a few different considerations in locating weld seams on low crown panels, such as the quarter panel. In most cases, as mentioned above, a seam horizontally through the middle of the panel is just asking for trouble as there is little shape (strength) in the panel to resist any movement/distortion from the shrinking, and why a weld here normally results in a severely caved in valley. (given no planishing to counteract the shrinking). For the most part one would put the weld up as high as possible, as most quarters have enough shape toward the top where the quarter slopes inward to help resist movement and distortion. It also puts the seam up where most if not all is better accessible for planishing. That is the normal scenario.

In other cases, perhaps the panel is blocked by an inner wheelwell or other structure that prevents/discourages planishing the weld. In this case, one can be creative in making a dolly on a stick, say a piece of steel flat bar that would fit in the void, welded to a pipe to allow better reach. I've also employed the assistance of my nephew in remote cases where his youth permitted more of a contortionist approach over what my body refuses to do anymore. This is also why it is important to planish those weld dots individually, and then grind them out of the way, front and back. This way two people can better work together on either side of a panel to planish out the welds, and find the correct weld dots in doing so. You also have the option of removing an outer wheelwell to better address an exterior panel that everyone will see, and then replace the wheelwell after you are satisfied with the metal bumping and finish work on the quarter.

Next, you can use features of the panel in your favor. Here is a lower replacement panel that I fabricated for the bottom of a 55 Chevy wagon lift gate, that has had no planishing performed, and looks to be one that will finish easily using only epoxy primer...









Other side.....











Any imperfection are slight enough that epoxy primer will take care of them. But as you can see, the panel where the weld travels through has a crown that protrudes outward in the horizontal plane, and inward in the vertical plane. So the shrinking forces tended to counteract each other, and the panel stayed exactly where it was. The weld's limited length also help out to limit the shrinking effects. So this shows a good example of using panel profiles in weld placement to limit distortion/panel movement while using the mig.

[Hotroddder]

I did my latest lower quarter panel patch with MPC's instructions in mind. Tack, grind down a bit and planish each a bit. Takes a bit more time, but the 10
square patch was probably the easiest to finish of all the patches I have done. Looking forward to the next one to see if it is the method or just a lucky one.

[MP&C]

Forgot about the welding wire.. I have recently changed from ER70S-6 wire to ER70S-7 wire, and have found the higher manganese content to improve wetting/flow and decrease proud height. In the singular weld form (one dot as opposed to a gap filling blob) it has shown to be slightly softer for easier planishing as well as grinding. Lower proud means less consumable used in the grinding process, but still sufficient proud on either side of the panel for effective planishing. Here's some samples of the -7 in a practice piece after setting up the machine, note the minimal proud height and consistency in weld size from front to back, works well for planishing singular welds without touching the panel..

For these first two pictures, I was playing with welder set up. First and foremost, the welder is set a little hot to promote a full penetration weld with each and every dot. Next, if you experience any blowout, then try adding more feed speed before turning down the heat. Any mig weld with sufficient heat and not enough fill is going to burn away at the parent metal, so control blowout with more feed speed. For this practice, I had the machine's heat set for 3/16 thick steel, and weld size was controlled by duration of weld, which in this case was about 1/2 second, and this is on 19 ga steel, which measured at .038" thick.. I'm not saying to use this same heat setting on your machine, but more to illustrate that one shouldn't be afraid of a little heat in producing full penetration welds. Do some similar practice coupons and vary your heat settings to see what works best for your machine.


Front of panel...



Rear of panel....



Here's a couple pics showing the grinding and overlap process.. Machine's heat settings were just above 16 ga in this case, feed speed slightly higher than machine suggestion for 16 ga, and weld duration about 1 second or so.

All clamped up...



First set of tacks...





Weld penetration, the back side....




Weld, planish, grind, overlap, repeat...




Planishing as you go helps to keep the panel's shape in check...



Still needs a bit of metal bumping but not too bad overall..

[rockytopper R.I.P 5-13-2017]

Wow thank all of you guys!!!! That explains the mistakes I've been making on my initial attempts to do this. Robert I have followed your lessons all a long thanks for putting this level of instruction all in one place. Great reference for the future. Perhaps a sticky should be made.

Dick, that didn't include you I already paid my dues $$$$ to you LOL just kidding. The lower front Qtrs are what I have to do on my nomad so I want to improve my skill set prior to attempting that.
Again thanks very much.
Rocky

[slowfinger]

Great post! We have learnd alot for future metal pannels on the 56 H.T. we have!