David,
75/25 is a very "known" shielding gas mixture….. for short circuiting transfer. I agree with Allan that you'd need at least 80% argon to be out of the short circuiting transfer mode. Factors that determine the mode of metal transfer are the welding current, wire size, arc length (voltage), power supply characteristics, and shielding gas.
To add to what Allan has said, with regard to the various modes, short circuiting metal transfer uses small wire diameters and operates at low arc lengths, low voltages and welding currents. The metal transfer occurs when an electrical short circuit is established as molten metal at the end of the wire touches the molten weld pool.
Globular transfer is a step up from short circuiting. the welding current and voltage are increased above the maximum recommended for short circuiting and the metal transfer will begin to take on a different appearance. The metal transfer occurs when the drops of metal that are typically larger than the wire diameter, move toward the weld pool under the influence of gravity. This type of transfer can be very erratic, can produce spatter, and can even short circuit at times.
Spray transfer occurs by increasing the welding current and voltage beyond than that of globular. When this is done, the metal transfer becomes a true spray arc. The minimum welding current at which this occurs is called the transition current. When the transition current is reached, small molten drops of metal are detached from the tip of the wire and projected by electromagnetic forces towards the weld pool. The transition current from globular to spray increases as wire diameter increases. For example, the minimum arc current for .030 wire is 150 amps. .035 is 165 amps, and .045, is 220 amps. Welding current, wire size, arc length (voltage), power supply characteristics, and shielding gas are all factors that determine the type of metal transfer. Short circuiting is rare with spray transfer, and there is very little spatter.
You mentioned that you didn’t want to use spray because it can’t be used out of position. That’s not entirely true. Spray is generally limited to welding in the flat position only because of the large weld puddle, but mild steel such as handrails, etc. can be welded out of position with spray when small weld puddles are used…. much like the welds used in handrails, when .035 or .045 diameter wires are used. My suggestion is to take this approach and use 98/2 shielding gas.
Pulsed spray welding is a variation of spray, with the current varying between a high and low value. The low level of current is below the transition current while the high level is well into spray. Metal is only transferred to the work during the period of high current. Usually one droplet is transferred during each high current pulse. Typically, only 60 or 120 pulses per second are used. Because the peak current is in the spray arc region, arc stability is similar to that of conventional spray arc welding. The period of low current maintains the arc and serves to reduce the average current. The pulse spray technique will produce a spray arc at lower average current levels than are required for spray arc welding. The lower average current makes it possible to weld thinner gauge materials with spray type transfer using larger sized wire electrodes than otherwise possible.
Again, my suggestion to you is to utilize the spray transfer mode using either an .035 or .045 diameter wire with 98/2 shielding gas.
I'm working from memory here, but I think I remember this coming up before, and the mode of transfer is not required to be on the WPS, and if that's the case, leave it off then there is nothing to argue about, and your inspector has no foot to stand on.
Although, that might be for FCAW, but check the table and see if it's required for GMAW. Good luck.
Yes
It looks like i would benefit from spray arc.
but is it cost effective??
I believe the mode of transfer is an essential variable whenever GMAW is used.
Some welding standards place few restrictions of the use of globular, spray, or pulse spray transfer. However, most all welding standards do place restrictions on the use of short circuiting transfer. The mode of transfer is required to be listed on the WPS for the welding standards I work with, including AWS D1.1, D1.5, ASME Sections I, VIII, IX, and various pressure piping codes. As for AWS D1.1 (2004 because it is handy) transfer mode is listed as an essential variable in Table 4.5, item 13. Certain variable listed in Table 4.5 are applicable to the prequalified WPS even when the WPS is not qualified by testing. Annex IV and Annex H are provided for additional guidance when writting a prequalified WPS.
Best regards - Al