Short Arc, Spray, or Pulse Process

By wbhawthorne Date 03-27-2017 00:11

Would appreciate some input on the best welding process to be used in our facility. We are a high production truck and utility trailer bodies welding facility using .035 70S6, 75/25 bulk gas mix, Miller CP 302 short arc process. We have the opportunity to upgrade our 45 machines over the next 5 years. We employ 70 welders over 3 shifts.

Welding gas and equipment suppliers are offering some confusing recommendations such as:

All joints .035 86/14 spray transfer process.
All joints .035 86/14 pulse process.
All joints .035 Tri-Gas mix pulse process.
Joints under 3/16 steel .035 86/14 pulse process.
Joints over 3/16 material no advantage to use .035 86/14 pulse process, use spray transfer.

We are joining steel thickness:

.075 to .125 to .188 to .25. with 1/8 - 3/16 fillet welds horizontal x 1.5" welds, vertical down x 1.5" welds, 75 degree down x 1.5" welds.
.38 to 1" with 3/16 fillet welds horizontal x 3".vertical down x 1"
.125 to .125 with 1/8 fillet x 1.5 welds horizontal and vertical down
.075 to .075 outside corner flat welds vertical down x 6"
.188 to .188 with 3/16 fillet + flat welds horizontal and vertical down x 1.5 - 3.0" robotic welding
.075 to .075 with .125 fillet & flat welds horizontal and vertical down 0.5 - 1" robotic welding

By TimGary (****)

Date 03-27-2017 11:43

The first step is to identify if your welding needs to be done to a specific welding code or specification.
I assume that the main requirements you need to meet are DOT.
Going from memory, I don't think DOT calls out specific welding requirements, other than to state that welding needs to be done in accordance with an approved procedure, and Welders need to be code qualified. I think it calls out AWS and/or ASME, but my memory may be failing as I haven't finished my first cup of coffee yet this morning.
Others may provide better info in this area.

Second step is to compile and document the efficiencies of your current process, which will provide a base line to measure against.
This will help to provide comparisons to other welding processes, to help select the best options that provide both increased welded joint integrity and increased efficiency.
This will also provide an estimable ROI to justify the expense of different procedure / performance qualification testing and possible new equipment.

Third step is to R&D different processes to see what has the best potential for overall improvement, so you can make an educated decision.

Short Circuiting transfer use in structural applications is restricted in welding codes due to it's inability to provide reliable weld penetration / weld joint integrity, especially when welding vertical downhill. It's also a very slow and spatter producing inefficient process.
Spray transfer is great for weld penetration and joint integrity, but has little to no open root and vertical downhill capability, which means that joint preparations have to be tightly controlled and welds have to be positioned flat or horizontal. Spray also has limited reliabilty on material thicknesses less than .1875" thick.
Modern pulse equipment with multiple waveform capabilities is highly versatile for all material thicknesses and positions. When done correctly, it can provide much more reliable penetration and weld joint integrity than short circuit, even when used in the vertical downhill position, can be tuned to create little to no spatter, and can run efficiently at 15 - 30 IPM travel speed, which I'm sure is much higher than your current short arc.

My recommendation would be to look closely at pulse with either Miller Continuum and Lincoln Powerwave equipment, with shielding gas of 90% argon / 10% CO2, or 98% Argon / 2% O2.

Tim

By Lawrence (*****)

Date 03-27-2017 12:39

I like Tim's response a lot.

Forget the Tri-mix, you can do what you like with excellence with several two part mixes.

Before you do trials on the new equipment and gasses... I would suggest you really take a close look at what you are accomplishing now.

Look at your current fillet sizes vs what they are supposed to be.
Look at your current travel speed for actual 1/8" and 3/16" fillets.

When you have a baseline to compare with, then you can let the different vendors supply you with a loaner unit to do some trials in-house with a couple of different bottled gasses. The 86/14 seems a bit high on active gas unless your material has heavy mill scale or some sort of coating. 90/10 or 88/12 Ar/C02 sounds more reasonable for what you are doing.

Look at GMAWP for your 1/8" and 3/16" fillets. You may also want to look at a less expensive .045 filler. It's surprising how GMAWP can produce smaller fillets with this size wire at a higher deposition rate and lower filler cost.

When you do your trials on the new stuff, make sure you perform some macros and break testing on your vertical down fillets... That can be a tricky weld that can look pretty good and still miss root fusion...

I think if you attempt traditional spray transfer, you will have great difficulty producing fillets the size you have called out.