Undercut pictures

[Steved]

Hi there.

Would it be possible for one of you more expereinced weldors to make a couple of passes showing undercut, overaperage and just right for tig, take a picture and post it?

I am not sure that I fully understand what undercut is or what it looks like and all of the pictures in the books I have are black and white and I cannot really see what is going on.

The good news is that I start my TIG course in the next three weeks and hopefully will learn tons! Really looking forward to it.

Thanks,

Steve

[Sberry]

I am not sure if i could run a bead with undercut,,,, hahahahahahaha

[HAWK]

Pictures

Steved,

Here is a picture from one of the first welding text books I studied. The book is by Raymond Sacks: Welding: principles and practices. I don't think it is in print today. However, it has some great information even though technology has far surpassed this text of the 1970's. Please see attached. This picture is courtesy of Kaiser Aluminum and Chemical Corp. I hope this helps. If it is not what you are looking for, let me know and I'll open up shop and make a few passes for you. BTW: Thanks for all you help on the phase converter.

[HAWK]

Steved,

What you are chasing is the middle bead. All three of these beads appear to made with a sinewave output. Since the squarewave and inverter machines offer myriad additional features over these dinosaur TIG machines your beads may look considerably better.

Sberry is probably right: It is hard to run an exaggerated undercut TIG bead because as you increase the amperage and continue adding filler your coupon metal will most likely sag and melt. It can definitely be done. However, I think a beginning TIG welder will have more difficulty running the undercut bead than a mostly correct bead. Try it and see. You tell us which is easier for you.

[Steved]

Thanks for the picture Hawk. I think that most of my welds are looking fine but since I have never gotten any feedback from someone who knows I am a bit hesitant to trust them. I keep hearing about undercut and things like that and since I am not *exactly* sure what to look for I am a bit nervous about the welds. A picture is no match for an experienced eye.

The good thing is that I am starting a beginner TIG course at our local technical college at the start of November and I am sure that I will get the feedback that I require. Hopefully my attempts over the past few months will assist me in the course. Actually I am a bit nervous about going but that is normal - hopefully the instructor will not take me aside and say "make sure you keep your day job". HA! LOL.

Finally, the help that I gave was nothing at all, I hope that you have been able to clear the table and start working on that phase conversion project.

Cheers,

Steve

[eric75]

example pics

Here are some pictures of undercut.

In this case I was trying to weld a set of driveshafts the weekend before a race. In order to not cook the CV joints which are 1" from the weld, I tried welding as hot and fast as I could for about a sixth of the way around, then let the joint cool to room temperature before continuing. Welding hot and fast actually puts less heat in the part. By the time the heat had transferred the 1" it had been soaked into a large amount of metal, so the temperature was reduced so it wouldn't melt the rubber seal. I obvoiusly got a little carried away, and some of the contamination you see is probably from the Tungsten disintegrating. The shafts held up though, most likly because they are way too heavy for the application.
In this particular jount, the undercutting isn't terrible becuase it is taking material away from an outside corner which doesn't carry any stress. In different joint geometries, that sharp reduction in thickness can cause a stress riser which is a common place for cracks to form.

I make no claim to be an experienced welder, and if there is any other insight you folks can offer based on my pictures, I will be glad to accept it.

[Steved]

Thanks for the pictures.

Perhaps my question is not clear enough. What portion of the weld is the undercut portion?

My understanding is that it occurs on the 'edges' of a bead. Is undercut when the base metal is higher than the bead because the bead was 'attempting' to melt through the base material?

Thanks for your input.

Steve

[bail76]

Undercut is a groove left in the base metal unfilled by filler metal. Undercut happens along the toe lines of a weld. Picture looking down a bowling alley if the lane was the weld and it had undercut the gutters would be the undercut. Sorry I know thats not a real good example. Good luck.

[cleaver]

Undercut is a groove left in the base metal unfilled by filler metal. Undercut happens along the toe lines of a weld. Picture looking down a bowling alley if the lane was the weld and it had undercut the gutters would be the undercut. Sorry I know thats not a real good example. Good luck.

So where are the gutters in the example pics? I understand your analogy but I dont see it in the pics..I would like to know about this aswell...and does this only happen on tig or other process aswell?

thanks too..

cleaver

[HAWK]

cleaver,

In the picture I posted the bead to the far left is way too hot, but there is no obvious undercut. In Eric75's drive shaft weld pictures where the outer most edges of the weld meet the base metal of the shafts is the undercut. The base metal has been melted away (cut into) and not completely filled back in by the weld filler.

[cleaver]

cleaver,

In the picture I posted the bead to the far left is way too hot, but there is no obvious undercut. In Eric75's drive shaft weld pictures where the outer most edges of the weld meet the base metal of the shafts is the undercut. The base metal has been melted away (cut into) and not completely filled back in by the weld filler.

Ohhhhh!! Now I get it, I was doing that tonight too..I welded some tubing with my friends exhaust and I noticed while tigging that I was just melting the base metal, but I was adding filler though. But does this mean that if im "undercutting" that im suppose to be adding WAY more filler rods? There are probably cons on undercutting...what are they?

thanks hawk for the explanation..

regards

[HAWK]

Eric75,

Nice work. You are correct that hot and fast actually puts less heat into the workpiece. These are very nice welds even though there is some undercut. It would be difficult to prevent undercutting in your situation. It was more important not to melt the joint seals than to have the weld toes completely filled.

[HAWK]

cleaver,

Undercutting is a natural part of the welding process or you are not getting good penetration. If the undercut is visible on the completed weld, then it is not the ideal weld. Either you are running too hot, too fast, or not adding enough filler. Hope this helps.

The biggest con to undercutting is lack of overall weld strength. A small amount of undercut may be okay in circustances like Eric75's drive shart weld. Sometimes there are not right choices, just the best choice available. That is what Eric75 faced with his project. He choose a hot fast weld to prevent the CV seals from melting at the expense of a small amount of undercut. In my review a very good choice on his part.

[HAWK]

By the way I specialize in aluminum where undercut is an atypical weld fault. There are a lots of problems aluminum can present, but undercut in not usually among them. I also do SS, Ti, mild steel, crome moly, dissimilar unions, and others. Aluminum is my favorite and titanium beta alloys are a second choice as they are extremely challenging.

[HAWK]

Steved and Cleaver,

Take a look at Eric75's picture now. I have exaggerated the undercut and pointed it out by red lines. I should be viewable by Adobe Acrobat version 4 ,5 and 6. Adobe Reader is available as a free download here.