Need advice for cutting welds

[DzrtRat67]

Ok, so I *thought* a good way to get some plasma experience would be to scavenge as many parts as I could from an unused contraption from an art car... basically a bunch of bed rails, unistrut, some tubing and some hinges that I wanted to cut as much apart at the weld joints as possible to save/reuse as much of the metal as possible.

Apparently, I ......A. suck at plasma cutting so far and.....B. Am a better weldor than I thought I was.

Starting with a 520D, 240V, DC, led reading 40+ and 60psi air, good clean ground, not very clean welds.... no problem starting/maintaining an arc. The plasma either had a lot of blowback towards me (if aimed straight into the weld) or seemed to just rem-melt the weld slag and push it farther under where it cooled and re-welded the pieces.

After destroying one set of consumables on several attempts at several welds, I tried turning DOWN the amps to around 30 on the LED and turned UP the psi to about 80, hoping this would create a little less slag (dross?) and higher air to blow it away from the pieces. This seemed to work a little better, but still wasn't giving me what I had envisioned.

I ended up just choosing to sacrifice a little of one or the other pieces and make my cuts thru plain metal.

Any tips on cutting welds cleanly? Keep in mind, most of these are tee joints and butt joints (on a vertical surface) so it's NOT a thing where I'm cutting straight down like we usually try to do... it's more of a mitre or bevel cut for lack of a better term. I also have a cpl lap joints I'll want to cut.

I'll try to post a cpl pix below. The top one is where I tried to cleanly separate a hinge from some pretty thin box tube... as I guessed, I burnt thru the box before the weld.
The others, you'll be able to see that when trying to separate some unistrut from plate, I got some pretty good lava flow style blowback.

Thanks for any feedback.

Joe

[ISKI]

The 90 deg cut should have been easy at say 75 PSI and 40 Amps. The cuts that are straight in, I wouldn't use a torch or plasma torch unless I was cutting through both parts. I think that the Plasma cutter should not be used for gouging. I just cut some 5/8 steel that was welded to bench, so I could not get a good angle, and with the welds, the thickness varies up to an inch.
If you don't break through to the other side, any plasma cutter will not work well, and just consume tips. I'll post some pics.

[SICFabrications]

they make a gouging tip for plasma, but in my experience, plasma just is not suited for scarfing or gouging... the 3 options are this: grinder and grind out the welds, gouging or scarfing tip for a acetylene or propylene and oxy torch (they are the ones that are bent a lil) or CAC (carbon arc cutting/ gouging)

the torch is great, but still gonna have dross and crap to deal with... the scarfing tips have a much larger oxygen hole in the center than a plain cutting tip, what it does is make the oxygen less aggressive as it leaves the tip allowing for a more controlled gouge.

the CAC is the best, it leaves perfectly smooth gouges and after some practice, you can get good enough to remove bearing races off a spindle and never even nick the spindle.... the drawback for CAC is this: first, you gotta have a constant current machine big enough to handle it. ive seen diesel drive machines flip over on their side that werent bolted down from the jarring of the dead short created by CAC. the next is the sparks... full leathers is a must and i even spray my pants heavily with water and keep em wet to keep me from catching on fire... the third is the noise... for me, minimum of 2 layers of hearing protection, ear plugs and ear muffs...

its loud, hot, messy, but will leave the most amazing clean gouges you will ever see...



as for the plasma, ive tried it and dont like it, it just dont quite have the "guts" to sweat welds out... hope i helped

[Kel Fab Creations]

As ISKI said, you are gouging and its gonna be messy since you aren't going through the other plate. I just angle the torch away from me so the blow back sparks aren't hitting me in the face. I'm not sure on your machine but most plasma's like to stay between 70-80psi no matter what amps ur using. Whenever gouging out welds you should use old/bad tips. On those pics you posted I would have used a die grinder but for places that you can't fit a grinder into the plasma works well. Some times I need to break a tack or two loose on tubing in a hard to reach place so I use the plasma without the ground hooked up so I don't accidentally putting a hole in the tubing.

[ISKI]

One thing you could try is to cut into the weld with a die grinder (as above as much as possible) next heat up the weld so it is nice and soft, and then take a cold chisel to it. I love the the old auto restoration commercial that stated don't use force, get a bigger hammer

One thing a I gave away when I got divorced was my hand held band saw. This thing and a few shots of old motor oil, did a lot of work for me.

[DzrtRat67]

Thanks for the replies guys. I've learned that it wasn't *all* me and my lack of experience with plasma. Got it.... plasma no good for this job, unless I sacrifice one of the pieces and cut around the weld.....otherwise.....die grinder. Cool ! I don't own a die grinder yet, but I do have a HF gift card. Yee-ha!

Joe

[ISKI]

Die grinders are sort of a staple for metal fabrication. Just don't try to make one from an large angle grinder and a 7-1/4 inch abrasive cutoff wheel. years ago I did just that, and was cutting car frames with my Milwaukee angle grinder until the thing bound up and kicked back. It ate through my leather glove and took a nice bite off the back of my hand. I could see the veins and tendons. I don't want to think about what would have happened without the leather glove.

[Ascinder]

I use a 4-1/2" angle grinder with a cutoff wheel. Works great and has clean straight cuts. The only issue I have had is getting it into tight corners. I am going to be using that and the plasma cutter to try and remove a bunch of suspension brackets and tabs from a vehicle frame. I am going to try and use the plasma to cut down the brackets to allow the angle grinder to fit into place to be able to cut.

[ISKI]

Just today had to do the same. I needed to save both parts as the arm is for my second cherry picker. I was in a hurry, so I spent about 60 seconds with the hacksaw, then a few good smacks with a cold chisel, and finally about fifty up and down bends.