Bumper build questions

Hey everybody, I just bought the PowerMTS 200 and am now gathering materials for a rear bumper build for the van. I have done a fair amount of stick welding, but I'm totally new to mig. I have done some research and it sounds like Argon or C25/15 is the ideal way to go, but its really not practical for me to have an Argon tank as I don't have the room. I could however have a small CO2 tank. But I am also going to be welding it outside so I'm wondering if I should just go with a flux core and no gas or if there is a flux core that would work well with CO2. I'm going with round tube mild steel 1.5"X.120" btw. Thanks a ton for any input you may have.

Buying shielding gas in small tanks becomes very expensive. If you go with flux core be aware that humidity will rune the wire within 3-4 months if you leave it in the machine. If you do use flux core I would buy it in 10lb coil and if it is going to be a while between uses, remove it from the machine and seal it in a plastic bag with some desiccant to remove humidity or better yet vacuum seal the bag. A nice way to store it is in a 5 gal. pail with a rubber sealed lid and an oxygen absorber pack in the bucket. Flux core wire does not like paint or heavy rust so prep will be important. Co2 will be the cheapest shielding gas to use but it will leave a lot of spatter. Probably the most widely used gas is 75/25 argon, co2 but a small bottle will not last very long. About the smallest I would use is 125 cu.ft. size . That size tank will probably last about as long as a 10 lb spool of hard wire. They do make dual shield wire but just suffice to say it is not what you want to use .
For outside use , probably flux core like Lincoln NR211 mp. It is very much like stick welding but you have more control over the weld puddle and gaps are much easier to fill than it would be with stick welding. If you have a way to block the wind you could use hard wire and gas but you will need to always block the wind , even a mild breeze will blow the shielding gas away.

Welcome to the forums, and congrats on the new machine!

I've been meaning to try pure co2 shielding gas, and just this week picked up a cylinder on CL. I've _read_ that pure co2 will work on 1/8" steel but haven't done it myself. Pure co2 gives better penetration but also runs hotter than argon/co2 mixes and is more likely to burn through thinner material. Flux core will leave a slag coating so you'll have some cleanup after you weld. Whichever way you take it, bear in mind you'll need to set the welder's polarity to accommodate the wire you use. Solid wire mig is electrode positive and flux core is usually electrode negative, so just remember to match the polarity of the wire you use.

Good luck on the bumper project- have you welded tube before? Might be an idea to practice coping and welding on tube before starting the final project. WeldingTipsAndTricks.com just started a how-to-MIG series that starts with how to set up the machine, and there are MIG with co2 and flux core videos too.

Let us know how it goes!

Welcome to the forum. A lot depends on what you are looking for. If you don't weld much, a small bottle of C25 could be all you need. I know plenty of people that just do the occasional repair or small project, and can go months on a small bottle, about the size of the welder (20-40 cuft), and a 2 pound spool of ER70S6. At the same time, some folks swap out large 330 cuft cylinders almost daily. The other thing is how do you want your welds to look, and do you plan on doing some post weld clean up. MIG with C25 can, in the right hands, leave a weld that is very clean and can just go right to painting or powder coating. While CO2 MIG and flux core are more like stick welding, where some slag chipping, wire brushing and even some grinding or polishing will be required to make it look nice, for something like a tubular bumper. As Gary mentioned, where you are welding also plays a big part. You can always start with a small spool of flux core and try it first. Then switch over to MIG and CO2 or C25, if you want to step up a notch or two.

My take. And all above ports are sport on.

If you think you will be welding a 2-3 times a week or 2-3 times a month and you can handle a 125cf tank (80 smallest), that is the bottom end of best price and will last for a bit.

On welding outside it depends on the job. Fixing a fence or landscape trailer on 50 acres nursery way in the back, I would use MIG with flux core (DCEN). For a bumper (for me or anyone) I would use MIG with C25 and ER70S6 (DCEP) so I would have no or little cleanup. Make a shield to block the wind, some days are not that windy so crank up the gas a little more. It's more of a get the feel of it and what you are looking for like Rambozo said.

Note, there will be some spatter and wood or cardboard can catch on fire if you make a shield from that type material. We always have an extra guy, welding blankets and fire extinquisheron hand.

I didn't know that about the flux core going bad, that is very good to know. Thanks for the reminder about switching polarity DaveO, Have you tried the straight CO2 yet? I've been eying some used cylinders myself. Argon just takes up so much space, the biggest I could get is like a 40 cf which would last around 2 hours maybe a little longer of straight welding. Doesn't seem like it would be worth the hassle. I've welded a little bit of tube in the past but some practice before I start would be smart. I'm going to make an undercarriage tire holder out of the same tube so I'll try that first as it won't be seen. I'm not so concerned about what it looks like but less clean up would be nice. I think I'll just pick up a small roll of flux and see how it goes. I checked out that video on CO2 and the splatter doesn't seem that bad and once he got it dialed in the welds looked pretty good too. So depending on funds I might have to make some wind blocks and give that shot after I try the flux. Thanks for all the information I'll let you all know how it goes and throw up some pictures in the next couple weeks.

Haven't tried the co2 yet: I picked up an empty 20# bottle but haven't exchanged it yet, and I still need to get a 320 to 580 adaptor. Life has been getting in the way recently, and I just haven't had a chance to get out to the LWS.

Good luck with your tube projects, and do let us know how it goes! Just in case it's helpful there's a FCAW welding calculator here:
http://www.millerwelds.com/resources...calculator.php
...that gives a starting point for getting your weld parameters dialed in.