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View Full Version : attn: Welding Gurus! Spray Transfer questions...



Krash80
08-23-2006, 01:20 AM
I got bored tonight and turned my MIG all the way up to the maximum settings just to see what it does, and I think I stumbled upon something pretty cool. At 32V and 700 IPM, I was able to get a REALLY smooth arc on some 3/4" plate. The process sounded more like a hissing noise than a crackle, produced almost no spatter, and made smoother beads than I've ever made with this welder (taking into account that I can stick weld really well but for some odd reason am having a rough time getting used to the MIG...I still like my old AC stick welder better!)

So does anyone know anything about spray transfer welding? I'm thinking this is what I was doing, but I'm not sure, and I know very little about the process. I did a google search but couldn't really find much explaining how to spray transfer weld or what the advantages of it were...about all I found was that it shouldn't work very well with the 75Ar/25CO2 gas that I'm using...but it seemed to work pretty well to me!

Any info appreciated...someone school me on MIG welding techniques like spray transfer and globular transfer, which to me are nothing more than advanced welding terms that I've simply heard of.

-Ron-

ProjectZJOM617T
08-23-2006, 03:23 AM
What model of welder do you have and what diameter and type and diameter wire are you running..

Too me with the 25% CO2 it sounds like you really just found the right setting for a thick material like the 3/4" plate. .

http://www.mig-welding.co.uk/forum/index.php

http://www.millerwelds.com/pdf/mig_handbook.pdf (http://www.millerwelds.com/pdf/mig_handbook.pdf)

http://asuwlink.uwyo.edu/~metal/migtech.html




There are three modes of material transfer in a wire feed machine. One is "blob mode", where the wire sticks, then melts locally, then breaks. This occurs at the lower end of the heat/wire feed range. I say heat/feed rate as a ratio, because this pretty much determines which deposition mode you will see. Blob mode welds are the lowest penetration and lowest transferre heat, because there's almost no real arc action, just mostly resistive heating of the wire and contact point.
The second mode as you move up the range is a soft arc with the metal being pushed through it. You'll recognize this mode when it happens; there's no more "wire push", the sound changes from a random snapping to a more uniform sizzle and everything just gets smooth. This is what I consider the ideal mode. The arc is stable but most of its energy is transferred into melting the fed wire and a localized area of the workpiece. In this mode I see about 1/4" of heat affected zone around the weld (automotive sheet metal thickness), and by proper setting I can get perfect penetration which I define to be some backside protrusion but no sag or burn-through. The handpiece ("gun") in this mode may have a buzzing feel to it but none of the bucking you get in blob mode. The third mode is when heat is much higher than the wire feed rate needs. This mode is akin to traditional arc welding, except with a fed wire. The arc energy now is biased more into the workpiece, with attendant heating and penetration. The wire still adds filler but there is more tendency to undercut, eat back and blow through especially on thin pieces. In this high heat/feed mode the buzzing/sizzling sound is replaced by a more purely electrical arc sound (whispering/crackling). This mode is desirable when welding pieces much thicker than the wire, especially when you haven't taken the bother of grinding proper chamfers and need to get penetration.

AprilzWarrior
08-23-2006, 11:35 PM
Ever see Claytons welds... need I say more ?


Blob mode... geez Im glad it doesnt say that on my Lincoln LOL

Jim311
08-24-2006, 12:05 PM
Haha.. I think when I was learning I perfected the "blob" method!

Krash80
08-24-2006, 03:11 PM
The welder is a 300A Millermatic. I'm using .035" ER70S-6.

From what I could find online, it definitely was doing spray transfer...it's an unmistakable "hiss" noise while welding as opposed to any sort of a crackle. Apparently it's how most robotic production welding is done (except they use a pulsed spray transfer) and it allows for very deep penetration with high travel speeds. Spray transfer can only be done well in a flat position unless it is pulsed.

I've also read that it can be done w/ 75% Argon, but it's very inconsistent when compared to 80% and higher Argon. I guess the ideal gas for spray transfer is 90% Argon, 8% C02, and 2% Oxygen.



I found this explanation of the 3 main types of metal transfer methods used when MIG welding:

In the short-circuiting mode, metal transfer occurs when the electrode is in direct contact with the weld pool. In this mode of metal transfer, the relationship between the electrode melt rate and its feed rate into the weld zone determines the intermittent establishment of an arc and the short circuiting of the electrode
to the workpiece. Specifically, the electrode is fed at a constant
speed at a rate that exceeds the melt rate. When it contacts the molten pool a short circuit occurs, at which time there is no arc.
The current then begins to rise and heats the wire to a plastic state. At the same time, the wire begins to deform or neck down due to an electromagnetic pinch force. Eventually, the current value and resulting pinch force causes a drop of metal to transfer into the weld puddle. At this point, an arc is established. This sequence repeats itself approximately 50 to 250 times per second. Since there is less “arc on time” established during the short circuit, the overall heat input is low, and the depth of fusion is relatively
shallow; thus, care must be exercised in selecting the procedure and weld technique to assure complete fusion when welding thicker materials. Due to its low heat input characteristics, the process produces a small, fast-freezing weld puddle which make it ideal for
welding in all positions. Short-circuiting transfer is also particularly adaptable to welding sheet metal with minimum distortion and for filling gapped or poorly fitted parts with
less tendency for burn-through of the part being welded.

Globular Transfer is characterized by the transfer of molten metal in large drops across the arc. This transfer mode takes place when
the current and arc voltage are between the short-circuiting and spray transfer current and voltage levels; it occurs with all types of shielding gas. Carbon dioxide yields this type of transfer at all usable welding currents above the short circuiting range. Globular
transfer is characterized by a drop size approximately two to four times greater than the diameter of the electrode. With carbon dioxide, the droplet is not propelled across the arc, due to the repelling forces acting upward toward the wire tip. These forces tend to hold the droplet on the end of the wire. During this time the drop grows in size and eventually either transfers by gravity due to its weight, or short circuits across the arc gap.

In Spray Transfer, the molten metal is propelled axially across the arc in small droplets. In a gas blend of at least 80% argon, when combined with the proper operating conditions, the electrode
metal transfer changes from globular to a spray or spray-like mode. The minimum current and voltage levels required vary for any given electrode diameter. The change takes place at a value called the globular-spray transition current. Spray transfer in argon is
characterized by a constricted arc column and pointed electrode tip.
Molten metal transfers across the arc as small droplets equal to or less than the electrode diameter. The metal transfer is axially directed to the workpiece. Since the metal droplets are small, the transfer rate can be as high as several hundred droplets per second. Due to puddle fluidity, spray transfer is limited to the flat or horizontal welding position.

ProjectZJOM617T
09-03-2006, 01:36 AM
I have been busy...

With that machine, amperage settings and wire diameter it is definately spray x-fer...

The biggest job I ever did with that was on a 72" bobcat sweeper bucket.. Someone drilled a manhole cover receptical edge with an old worn out bucket w/o the cutting edge bolted to it. I had to replace about 12" x 72" of plate on the bottom of the bucket and weld on a new cutting edge mount plate (I think that was 3/8" x ~ 5" x 72") ... All joints were overlap and welded on both sides fully across the seam.. A few inches at a time to avoid warping.. If it was a narrower section like the ends of the cutting edge mount I'd do it in one shot. Shooting 72" across in one run did'nt seem like a good idea so I did it in 6" increments..

The spray transfer subprocess is the sh&t for thicker stuff like that when you can have the work laying horizontal..

Krash80
09-03-2006, 12:51 PM
thanks for reminding me...i need to fix the hole in the bottom of my toothed bucket for my bobcat! :D