I'm contemplating a hack and have been too afraid to even ask

[MJM]

As Chris mentioned, a repair like this will show a ghost line, yes, even through your filler work. Note the horizontal ghost line just up from the bottom of the tailgate in this video. What a Flange repair gets you.

Do Ghost lines happen from butt welding panel patches if the welds are not dressed properly? As an example, the weld is dressed but there is a slight trough in the weld joint that will need to be covered with filler. I'll also use Bad Chad as an example. I would say 95% of the time when he butt welds, he grinds the weld but leaves it high and buries it under fiberglass filler. Will that Ghost?

 

[shine]

if the proud is left thick it will ghost in the sunshine and go away when cooled down. i try to get rid of all the proud . a mig can be your friend or your worst enemy .

 

[D.A.T.]

Do Ghost lines happen from butt welding panel patches if the welds are not dressed properly? As an example, the weld is dressed but there is a slight trough in the weld joint that will need to be covered with filler. I'll also use Bad Chad as an example. I would say 95% of the time when he butt welds, he grinds the weld but leaves it high and buries it under fiberglass filler. Will that Ghost?

-if he is cutting a trough along his weld with a thin disk--he is leaving two unwelded sharp edges--in the worst possible place--on the surface. A light coat of filler won't expand at the same rate as the steel edge below it and you will be able to see it in the hot sun. If he is leaving his weld crowns high and burying them in filler--my guess is he isn't too sure he is getting good penetration on the back. Same problem as below in reverse in cold weather with an unwelded inside edge.

In butt welding two panels --one a patch like a long lower door-skin--any unwelded long edge is unable to transfer heat to the surrounding metal and will expand more so than what it is supposed to be attached to. You need to have a full pen weld to alleviate this. Since the patch weld seam edges ares restrained by the folded edges of the patch attaching it to the door frame the only way the edge can gain length is to grow is up and out--toward the heat source. That would be the longest worst case cumulative growth. Hence you see that edge "protruding proud" out of the paint in the sun. Set it outside in -40F--you will see something else. The growth or contraction is 6.5 millionth of an inch/inch of edge per degree F change.

 

[Tungsten]

This is a good thread. Lots of info. I’m a newbie this was one of my first patch panels. Rear wheel wells on 07 GMC 2500. I assume the weld seam shrunk leaving this void low spot as seen in pic. I filled with fibreglass filler. Will this show ghosting it’s about 6 months old.nothing so far but really haven’t looked. Cold winter is coming Thanks.

 

[shine]

in texas yes. i have a black coupe i did in 95 . the runk lock hole would ghost in the sun a little. that pround needs to come off.

 

[Treeslayer]

in texas yes. i have a black coupe i did in 95 . the runk lock hole would ghost in the sun a little. that pround needs to come off.

mr Shine you mean he should have ground the weld down farther? his work looks about like mine but i did take it down closer than he did.
i admit i was hesitant to grind that much but i was sure i got full penetration. i reasoned it had to be no thicker than the metal.

 

[MP&C]

This is a good thread. Lots of info. I’m a newbie this was one of my first patch panels. Rear wheel wells on 07 GMC 2500. I assume the weld seam shrunk leaving this void low spot as seen in pic. I filled with fibreglass filler. Will this show ghosting it’s about 6 months old.nothing so far but really haven’t looked. Cold winter is coming Thanks. View attachment 27140

What does the weld look like on the back side?

 

[D.A.T.]

This is a good thread. Lots of info. I’m a newbie this was one of my first patch panels. Rear wheel wells on 07 GMC 2500. I assume the weld seam shrunk leaving this void low spot as seen in pic. I filled with fibreglass filler. Will this show ghosting it’s about 6 months old.nothing so far but really haven’t looked. Cold winter is coming Thanks. View attachment 27140

That's a good picture that illustrates what another person here was talking about with "remove the proud" as a normal course of eliminating variables that can cause problems. The grinding of the weld' surface reinforcement have left sharp edges down the length of your weld from "flat topping" the reinforcement. Sharp weld toes (where the weld merges into the base metal) can also be a problem when left on the surface. Nature abhors sharp edges--they are the failure initiation for many things--welds and paint included. The very sharp edge will grow and expanded/contract more. It has only one path to give up its absorbed heat. Yes, you could have these edges expanded when heated and show depending on the temp. The winter would have a heated cab and a cold outside resulting in something different.

 

[MJM]

-if he is cutting a trough along his weld with a thin disk--he is leaving two unwelded sharp edges--in the worst possible place--on the surface. A light coat of filler won't expand at the same rate as the steel edge below it and you will be able to see it in the hot sun. If he is leaving his weld crowns high and burying them in filler--my guess is he isn't too sure he is getting good penetration on the back. Same problem as below in reverse in cold weather with an unwelded inside edge.

In butt welding two panels --one a patch like a long lower door-skin--any unwelded long edge is unable to transfer heat to the surrounding metal and will expand more so than what it is supposed to be attached to. You need to have a full pen weld to alleviate this. Since the patch weld seam edges ares restrained by the folded edges of the patch attaching it to the door frame the only way the edge can gain length is to grow is up and out--toward the heat source. That would be the longest worst case cumulative growth. Hence you see that edge "protruding proud" out of the paint in the sun. Set it outside in -40F--you will see something else. The growth or contraction is 6.5 millionth of an inch/inch of edge per degree F change.

^^^ ...... I'm trying to wrap my head around the comment highlighted above. You've giving a solution by applying a full pen weld. I guess I just learned that heat in metal doesn't disapate to the atmosphere first until it has traveled as far as it wants to in metal first, that being up, down and out.

I've read some of your other replies in threads with regards to metal properties and how they react. This is another area I'm trying to wrap my head around.

 

[Tungsten]

What does the weld look like on the back side?

No pic. IIRC it wasn’t that good. Could barley see only really could feel as all I did was cut a little of the rusted inner wheel house.out. I don’t think the weld penetration was good. I did the cut and butt method so gaps were pretty tight for a newbie.

 

[Lizer]

@MP&C --I'm slowly working through all your posts, but have had a lot of stuff going on. I do planish my welds...sometimes. But why do you planish before grinding the proud weld down and not reverse order?

Regarding my patch--do you think I should attempt to slice it open once again to relax the metal, with a 3" cut off wheel making the cut at an angle through the metal to minimize the gap, and try reweld using your methods?

 

[Treeslayer]

That's a good picture that illustrates what another person here was talking about with "remove the proud" as a normal course of eliminating variables that can cause problems. The grinding of the weld' surface reinforcement have left sharp edges down the length of your weld from "flat topping" the reinforcement. Sharp weld toes (where the weld merges into the base metal) can also be a problem when left on the surface. Nature abhors sharp edges--they are the failure initiation for many things--welds and paint included. The very sharp edge will grow and expanded/contract more. It has only one path to give up its absorbed heat. Yes, you could have these edges expanded when heated and show depending on the temp. The winter would have a heated cab and a cold outside resulting in something different.

i think i understand, its like a sharp edge inside a cylinder head that creates a hot spot and causes detonation. no sharp edges.

 

[Treeslayer]

Lizer your thread has blown up lol. i appreciate the knowledge shared, i hope you get sumthin out of it as well.

 

[dhutton01]

Won’t cutting and welding the same joint three times work harden the material to the point it is very brittle? Asking for a friend…

 

[D.A.T.]

Won’t cutting and welding the same joint three times work harden the material to the point it is very brittle? Asking for a friend…

No, another weld simply anneals the previous one...... Brittle fracture is defined to be ductility less than 15% for carbon steel. For people using short-arc MIG--The problem with ER70S-6 MIG wire is the spread between its yield strength and tensile strength is a lesser range at room temperature. It usually stretches around +35% in tension before it breaks. Planish it once and it gets tough--not brittle--beat on it some more less stretch to the point of little movement then shear fracture if you keep beating on it. You lose your malleability fast. The wire is loaded with more manganese than the sheet steel.

 

[MP&C]

@MP&C --I'm slowly working through all your posts, but have had a lot of stuff going on. I do planish my welds...sometimes. But why do you planish before grinding the proud weld down and not reverse order?

Regarding my patch--do you think I should attempt to slice it open once again to relax the metal, with a 3" cut off wheel making the cut at an angle through the metal to minimize the gap, and try reweld using your methods?

For using MIG, I set the heat high enough to get full penetration weld with each singular tack, wire feed faster (as needed to prevent blowout), and duration of trigger pull shorter to keep the weld flatter. Practice is suggested to get the welder dialed in prior to working on your good panel.

The weld is going to swell when it heats up and when it cools it will shrink slightly more than it’s original state. For a single tack by itself, it will shrink/ pull inward from all directions (circumferential shrinking). For any attempt to stretch this back out without adding in too much stress, my thoughts are that you will get more stretch out of a larger weld tack than after it has been ground down to panel thickness. Having a weld proud front and back means any planishing attempt should hit the weld dot only (and push the stretch outward circumferentially) for an easier effort in keeping the panel flat. If the weld were ground down, or if there were multiple welds , it’s more possible that the panel could get deflected. And for returning the panel back to its original shape (removing any wave), that is an easier task early in the process when the shrinking effects we are trying to correct are isolated to the one weld tack.

Also, if you were to grind flush first, any planishing effort is going to thin the area thinner than panel thickness.

Before cutting out and rewelding, I would rather see some profile templates at the weld, one inch and two inches away from the weld, and across the weld. If you have done no or minimal planishing, I would expect to see a sinusoidal wave just above and below the weld. Weld shrinkage is pulling things together, and the area just outside this is buckling up and down as the unshrunk metal looks for somewhere to go as it’s being pulled along for the ride. I’d try some planishing first.

 

[MP&C]

No pic. IIRC it wasn’t that good. Could barley see only really could feel as all I did was cut a little of the rusted inner wheel house.out. I don’t think the weld penetration was good. I did the cut and butt method so gaps were pretty tight for a newbie.

First and foremost you need to set your welder up for full penetration welds. Ie, a weld proud front and back. The “cut and butt” terminology suggests a Fitzee follower. I haven’t seen many of his followers that knew how to set a welder hot enough for a full penetration weld. I’ve seen his videos where he needs to come back and weld the back side due to poor weld penetration. More heat is needed and you should have weld proud on both sides of the panel. Our intent with welding in a patch panel should be to duplicate the one-piece panel that was there previously. That would include a full penetration weld that could could be ground flush on both sides, thus duplicating the original panel.

 

[MP&C]

This is a good thread. Lots of info. I’m a newbie this was one of my first patch panels. Rear wheel wells on 07 GMC 2500. I assume the weld seam shrunk leaving this void low spot as seen in pic. I filled with fibreglass filler. Will this show ghosting it’s about 6 months old.nothing so far but really haven’t looked. Cold winter is coming Thanks. View attachment 27140

Don’t take this the wrong way but the only people online that push using fiberglass filler over welds can’t weld themselves. They use the filler for strength as they don’t have full penetration welds. You don’t fix weld problems with fiberglass filler. Fix the weld problems. Find you some other mentors.

 

[chevman]

No, another weld simply anneals the previous one...... Brittle fracture is defined to be ductility less than 15% for carbon steel. For people using short-arc MIG--The problem with ER70S-6 MIG wire is the spread between its yield strength and tensile strength is a lesser range at room temperature. It usually stretches around +35% in tension before it breaks. Planish it once and it gets tough--not brittle--beat on it some more less stretch to the point of little movement then shear fracture if you keep beating on it. You lose your malleability fast. The wire is loaded with more manganese than the sheet steel.

ER70s-2 Will help
https://www.ebay.com/itm/2945356368...006&customid=5f6bf6c9ae7336cfcf9e4ddafac789bb

 

[MP&C]

Do Ghost lines happen from butt welding panel patches if the welds are not dressed properly? As an example, the weld is dressed but there is a slight trough in the weld joint that will need to be covered with filler. I'll also use Bad Chad as an example. I would say 95% of the time when he butt welds, he grinds the weld but leaves it high and buries it under fiberglass filler. Will that Ghost?

The ghost line shown in the video I linked was fully welded. It’s my understanding that it stems from two thicknesses of metal expanding and contracting slower than the single layer next to it. These differing expansion rates are what eventually causes the ghost line, even through filler. Think of how thick a weld proud can be, sometimes 3 or 4 times the panel thickness, and how the ghost line shown was created by only two panel thicknesses. The other consideration is that planishing helps to normalize the stresses across the weld so it more acts like the single panel that existed prior. Having weld proud left behind can’t help, in any regard.