Porosity in mig weld after cutting on table

[tylersims97s@gmail.com]

Hey everyone this is my first time posting to a forum but I am all out of ideas I have a 4x8 stv table with a 45xp Hypertherm and after cutting metal out I weld and grind the outside corners before grinding the weld looks great but underneath is full of random porosity and I can’t get it to stop some things I’ve tried is 6 different 75/25 bottles from 2 different suppliers 3 different welders 1 being brand new new regulators,liners,tips 5 different brands of er70s6 wire and my metal supplier sells me p&o steel so I thought that might be a problem so I bought regular hot rolled still same issue all pieces are thoroughly grinded then cleaned with paint thinner tried gas cfh anywhere from 15-60 also not a newbie to welding I’ve welded on the road for 8 years

[djreiswig]

Are you grinding before you weld? Plasma cutting produces nitriding on the cut edges. This doesn't weld very cleanly.

[acourtjester]

What flow is your gas at, it sounds like you are loosing gas coverage from wrong flow rate or wind blowing the gas away from the weld area.

[tinspark]

Ditto what acourtjester mentioned. Be sure that you have no airflow nearby. Also if you are using an exhaust arm keep it a few feet away because that will suck atmosphere into the shielding area. also when you finish your weld bead, do not move your gas nozzle away from the finished weld bead until the weld pool solidifies. You will get porosity from this bad practice too. Welding too hot for a given joint can cause this. Especially corner welds. Try dropping your weld settings 1 or 2 gauges lighter and practice with this. So if you are welding 12 gauge play with maybe a 16 gauge or even an 18 gauge setting especially downhill cornrers.
Also use no more than a 3/8” wire stickout.and If your gun is too far away, you will not get the gas coverage needed. stickout is the distance from the base metal to the contact tip. Too much stickout will definitely cause poor gas coverage, and colder welds (popping and sputtering etc).. Use tip dip to keep the spatter from building up in the nozzle.(aka nozzle gel) excessive spatter will block gas flow. Also almost weekly I find at least one of my students (sheet metal apprentice welding class) pull the insulator and nozzle over the gas diffuser and block the gas discharge holes.

Your problem is easy to diagnose and fix. Try some of the suggestions above. And maybe think about taking a semester of welding at a local city college. Most areas offer a night class so that it doesn’t infringe on work……. Hope something here helps
My 2 cents …ok maybe that was 3 cents

[tylersims97s@gmail.com]

I appreciate the help for sure I’m fixing to try the lower amperage and my gas rate is on 30 right now and it’s not me I can about guarantee I’ve welded all over America in nuclear plants and power plants and made thousands of xray welds and trust me I was about to loose my mind and thought maybe it was me I’ve brought 5 other welders in to weld it to and all the same I even made them reset the machine to what they would do to be sure the metal is grinded more then any other I’ve done just to be sure that wasn’t the problem and I welded 2 pieces together about 5 foot long I cut with a torch and no problem with it at all it’s got to be something that’s happening during cutting someone told me to drop my water about 3 inches in my table so we are trying that right now

[TJS]

I have tig welded my plasma cut edges and found no issues of course after clean bright shiny edges. You have my curiosity peeked. I have to give it a try without any cleaning and see what happens. Although I am a creature of habit and have to stop myself from prepping to test this out.

[ROKCRLER]

Ive noticed the same, porosity diminished and even disappeared after cleaning the cut edges with a flap disk.
Aluminum definitely needs to be ground down and cleaned, I mostly weld carbon and noticed cleaner welds after edge prepping.
I hate the extra step, but it's easier than grinding out a bad weld and rewelding.

[TJS]

All my welds in this thread are tig welded and plasma cut on my table. The fist pic is welded on a plasma cut edge and the tube cap in the second pic too. I did sand these with the blue sanding belt set up mounted on my bench grinder.

https://www.plasmaspider.com/viewtopic.php?f=12&t=35555

[tinspark]

my gas rate is on 30 right now

also try to drop your gas rate to maybe 15 cfh. I have experienced porosity with too much gas believe it or not..
The theory is as the gas is blasted at a high rate it pulls atmosphere in behind it. it is like a venturi effect.

Also, if you weld angle iron and other shapes (ie. non-cnc plas cut material) Do you have the porosity problem?
If not, then it seems to narrow it down to something from the plas-table

Also, I missed the last part of your original post that you are an experienced welder. Or I would not have suggested welding classes.LOL!
My bad!! and thanks for not taking offense.
I too am curious about what is going on with that porosity issue. You should be able to narrow it down to either a plasma cutting issue or not.
Keep us posted

[tylersims97s@gmail.com]

Yes I’ve welded non plasma cut pieces and no porosity at all we dropped the water yesterday and that seemed to help a lot still not 100% happy but it is much better

[djreiswig]

What are you using for additives in your water pan?

[tinspark]

Yes I’ve welded non plasma cut pieces and no porosity at all we dropped the water yesterday and that seemed to help a lot still not 100% happy but it is much better

Well that certainly narrows it down. No more need for swapping out welding machines.
I was using a water pan and switched over to a downdraft system, which works good for my setup.
But I have never experienced a notable porosity issue when I had my pan.
I switched because I had more mess, and my shop had a free exhaust fan sitting in their bone yard that I was given..

[tylersims97s@gmail.com]

I’ve been running straight water

[Jason@bc]

I have had the same issue....on and off, some pieces had porosity (when welded as they come of the table) and then the next ones were good, so I'm not sure what the cause is, could it be the steel???

[tylersims97s@gmail.com]

I’ve tried different still from different suppliers

[acourtjester]

Well it may be time for the old "virgin in volcano" to make the welding gods happy.

[tinspark]

Maybe try "backstep welding" or even "skip welding". No more than 1-1/2" or so at a time.
If you still see it, drop down to 1". This way the weld doesn't get hot enough to boil out whatever C&@p that is working its way up to the surface.
This has fixed this problem for me in the past when i have had similar and mysterious porosity.
And the many start and stops should not even be an issue if you will be grinding the welds out.
All of the start and stops are not as appealing as the stack of dimes look that we all are looking for after a weld. But porosity is much worse. imo
I have a hunch this may fix it. But it still sucks to do all of the careful and meticulous prep work expecting perfection when the project is completed only to find the weld is what is the deal breaker.
Also, as a sidenote, backstepping eliminates a lot of the warping, which is why most use this method in the first place. and is use a lot on stainless steel
Let us know how it goes

[Deezl Smoke]

Try preheating the cut edges before welding and see if that dries out any captured water from the instant contraction of water hitting a molted edge.

[Rocketdc]

When I first got my plasma table I had the exact same experience, the majority of my mig welds on plasma cut edges had porosity after I ground them down. I'm 99% sure the nitrided edge from the plasma cutting produces something that contaminates the weld. If you grind the plasma cut edges past the thin nitrided layer you'll have no problems with your welds.

[hardworker]

Rocketdc is 100% correct.

[tylersims97s@gmail.com]

Well after a lot of money and time it’s fixed one of two things fixed it we let the water level down 3 inch’s under metal and added another filter system right before plasma and all seems to be good now

[acourtjester]

Thanks for the reply, nice to show what fixed your problem, helps for future searchers

[jimcolt]

An air plasma cutter uses air as its plasma gas. Air is roughly 80% nitrogen and 20% oxygen. When you cut steel with this combination expect to get a thin nitride layer that is very hard, and that when directly welded will come out of solution and provide porosity in welds. This nitride layer on the cut edge is typically only .006" to .010" thick, and can be easily removed with a grinder/flap disc.

To eliminate this issue....oxygen plasma cutting systems were developed, such as the XPR systems and the MaxPro 200 from Hypertherm. They are more expensive, but produce better cut accuracy, cut quality and eliminate the hardening and weld porosity issues. Note, do not use oxygen as the plasma gas in an air plasma. Jim Colt (43 years of plasma cutting!)