Help me do better: Welding exhaust

Trying to fab up a full exhaust for my LS swapped Colorado. My welding experience is limited. My method is to use a pipe expander and slip in the joints before welding. This is my result so far and it's crappy. 

I put a pressure tester (thanks old DSM boost leak tester) and the welds leak. Bad. 
 

Any advice on the welds? Im using a flux core unit from Harbor Freight. https://www.harborfreight.com/easy-flux-125-amp-welder-56355.html?utm_source=google&utm_medium=cpc&utm_campaign=12236956207&campaignid=12236956207&utm_content=119984461169&adsetid=119984461169&product=56355&store=&gclid=EAIaIQobChMIu_Pog5Sk-QIVezizAB1ztgkbEAQYASABEgJfhvD_BwE
 

It allows settings to be changed for amperage and wire speed. Think I should revise settings? Again. Weld noob.

Try more heat, less wire speed.  Do a series of stitches.  Clean the slag from the previous spot before pulling the trigger again.

Each of those pits/holes is cause by some form of contaminant that ends up in the weld puddle. The contaminant vaporizes and when it escapes as a hot gas, it created the hole because it is spewing out of the puddle.

Aluminized pipe is great for not rusting, horrible to weld. You really need to get the coating off or you will have issues.

A wipe with IPA or Acetone will help get rid of oils.

If welding old pipe, keep in mind that crap inside the pipe will contaminate the puddle the same as crap on the weld seam side.

If you have scrap, cut it so you can hammer it flat and thus practice on flat surfaces. Much easier than the curved surface of the exhaust tube.

My first thought is that you forgot to turn the gas on 

Flux core is really hard to get a clean good looking weld, even when everything is perfect. 

Ditto to petes.

I looked at that and said turn on the gas.

Flux core welding gear should not be marketed retail. They sell the illusion of welding.

If it's portable you can bring it down here and use my gas welder

In reply to bentwrench :

I have done some very good flux core welds.  Even on sheetmetal.  But, big caveat, I had also been well experienced with MIG, and sort of knew what to expect with flux core welding.

The hardest part IMO is that you cannot see the puddle you are making and trying to push around, so you kind of have to go by instinct.

I've made hundreds if not thousands of passes with flux core.  It's how I started before I could afford a "real machine".  Few if any of those welds looked much better than the OP's but I never had one break.  They were all very effective.  Flux core has its place.  I think the internet though has raised everyone's expectations - perhaps too much.  One does have to consider CO and all that on an exhaust system, but my guess is that this weld is functional if not aesthetically pleasing.

Did you grind the coating off before welding? 
 

also make sure you are really watching your puddle. Ive seen welds that bad(sorry..) when people try to mimic the hand motions they see the pros do instead of watching the puddle and feeding it.  

TJL (Forum Supporter) said:

Did you grind the coating off before welding? 
 

also make sure you are really watching your puddle. Ive seen welds that bad(sorry..) when people try to mimic the hand motions they see the pros do instead of watching the puddle and feeding it.  

I didn't grind it before welding. This seems to be the contamination Pete talked about.

And you're right about the hand motions. I assume I should just be doing a steady drag and not the circular motions. 

And I agree. My welds are real bad. This is the last place on the internet I could post this without getting laughed at and ridiculed without any advice on how to improve. So thanks. 

I dip the ends of each pipe in muriatic acid in a plastic pan, 1/2 to 3/4" deep is good for a butt weld. Soak till no bubbling. Removes coatings and rust inside and out. Rinse ends with water to neutralize the acid, dry and wire brush before welding. 

What others have said.  More heat or less wire speed.  (maybe both).   

Getting rid of the aluminized coating should help you see your puddle better.

Scotty Con Queso said:

TJL (Forum Supporter) said:

Did you grind the coating off before welding? 
 

also make sure you are really watching your puddle. Ive seen welds that bad(sorry..) when people try to mimic the hand motions they see the pros do instead of watching the puddle and feeding it.  

I didn't grind it before welding. This seems to be the contamination Pete talked about.

And you're right about the hand motions. I assume I should just be doing a steady drag and not the circular motions. 

And I agree. My welds are real bad. This is the last place on the internet I could post this without getting laughed at and ridiculed without any advice on how to improve. So thanks. 

Your motion may be fine, but you need to watch the puddle.  Focus on one side of the weld, then move over just enough for the focus of the arc to be on the other side.  I'd start on the inside tube, then move over to the outside one.  Don't move enough that the arc leaves the puddle.  

I tend to burn hotter than most,  for a shorter time,  if I'm on light sheet metal or exhaust tube.  

Consider stacking tacks. Four tacks to secure the pipes in position first. Start your weld with heavy tack, when the 'cherry' goes out move about half a tack over and heavy tack again. Repeat all the way around the pipes. 

Dunno if I'd run a continuous bead on lighter gauge pipe. It can produce a lotta heat fast, then poof... blowout. Heavier gauge may be okay. 

Of course, practice first on your settings.

Exhaust pipe is awful to weld and the flux core wire isn't helping.

Wire wheel the pipe ends then wipe down with acetone before welding to make sure it's as clean as possible.

Hot slag will feel great inside those safety moccasins.  

Don't try so hard to avoid butt welding (non-slip fit).  In a case like this, it might actually help you avoid engaging some of the contaminants on the inside of the pipe.  Aim for cleanliness (perhaps above all else) and a tight fit.

Make sure you have the polarity set for electrode negative. Stick out length of the electrode is critical that looks as if you have too much stickout. 

Read the Lincoln electric FCAW welding guide, free on the internet

I'm going to echo the overlapping tacks, zap-zap-zap-zap comments.  I did a lot of exhausts that way with the earlier $80 Harbor Freight fluxcore welder, you don't have to pause super long between tacks if you're trying to get it done quickly and the leftover heat might even help.

That said, once you weld with a proper gas setup you'll never want to go back.

Slow down your hand, use gas and make inverted letter "C"s over the slot.

Got any scrap muffler tube?

ShawnG said:

safety moccasins

This made me lol. 

And thanks for the awesome responses. I have a plan in my head to move forward. Plus plan B and C.