Multipass GMAW Welder Settings

I need to weld together a couple pieces of 1”x3” CRS end-to-end (take two short ones and make a long one). The plan is to use a double-V groove, 1/8” root gap, with a 60 degree included angle. First a root pass, then flip the work, grind to clean metal, another root, then flip back and forth for filler/cap passes. This is all flat work on a bench.

I have a Miller Shopmaster 300 AC/DC power source with a Millermatic S-52A wire feeder and C25 gas at my disposal. When the welding is complete all surfaces (4 sides) will need to be ground down flush with the parent material. There are no specs called out on this weld – it’s just a case of not having long-enough material available. Grinding will be done with an angle grinder and hard disk/flap wheel, so nothing too critical there, either

This is a process I have done successfully several times in the past but I’m trying to refine the process and save some grinding time. Previously I was using a 90 degree included angle which means more welding and larger area to clean up.

The question is, what settings are recommended for a weld like this? I haven’t had much luck finding any wire speed/voltage recommendations for multi-pass welding. Again, I've made it work before, but there is always room for improvement. Thanks.

I will just say to add some run off tabs on both sides of the bars. This lets you start and stop the weld off the main material. Just cut them off with a cutting disk when done. Most common place to have a problem is starts and stops, so when you do not have them in your weld all is better. You should be turning down the heat as the material heats up also.
You dont mention what wire you will use, I would do it with dual shield but if you only have solid wire it is probably ok too.

If you are doing a double bevel on both sides you will (should) only have 1 root, full pen. .125 opening is a bit large, I'd go with somewhere around .09375 with a .062 land on each piece. I'm assuming you are going to burn .045 but that will work with .035 too. The tabs will help a bunch just make sure your wire is towards the leading edge of the puddle. If it starts to keyhole too much try going a little faster or opening up your weave width. You can climb a bit higher in the bevels but you really want to keep it tight in the root opening.

Good advice above. I’d add that for a weld this short (3”), any parameters you did find that were specific to “multi-pass” welding wouldn’t really apply. Normally, you go hot on your first pass or two after the root, to ensure good fusion and minimize flux or slag inclusions, but unless you let it cool, you are going to have a lot of heat in the work still on this one.
Grinding after each pass is another way to minimize problems with lack of fusion or slag. Be sure to use a wheel that hasn’t been used on anything but clean steel or you can make things worse, if it’s got aluminum or paint caked on it for instance.
It’s a simple little weld really, don’t over think it. keeping it reasonably straight is going to be your biggest challenge, as I’m sure you will discover!

Forgot to mention - 0.035 solid wire. I'll close up the root gap and see about the run-off tabs. I've been clamping the pieces to another length of scrap 1x3 to help keep everything straight so I'll have to come up with something different to accommodate the tabs. I appreciate the suggestions.

For the welder settings on that (assuming .035” S6 hard wire with C25 gas) I’d prolly set 320-340IPM wire @ 22volts, should run around 160-170amps.

Good luck,
Matt
On edit, attached cheatsheet with torch travel speeds for automation or WPS work.