MIG Wire Charts Page 2 - Airgas.com

Welding Help
MIG Welding Charts Page 2
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MIG Wire Chart Page 3

MIG Welding Techniques

1. Keep a 1/4 – 3/8 in. stickout (electrode extending from the tip of the contact tube) (Refer to Diagram 1).

2. For thin metals, use a smaller diameter wire. For thicker metal, use a larger wire and a larger machine. See machine recommendations for welding capacity.

3. Use the correct wire type for the base metal being welded. Use stainless steel wires for stainless steel, aluminum wires for aluminum, and steel wires for steel.

4. Use the proper shielding gas. Please refer to the “Selection of Shielding Gases” tables on page 4 of Radnor Catalog.

5. For steel, use ER70S-6 wire when more deoxidizers are needed for welding on dirty or rusty steel.

6. For best control of your weld bead, keep the wire directed at the leading edge of the weld pool.

7. When welding out of position (vertical, horizontal, or overhead welding), keep the weld pool small for best weld bead control, and use the smallest wire diameter size you can.

8. Be sure to match your contact tube, gun liner and drive rolls to the wire size you are using.

9. Clean the gun liner and drive rolls occasionally, and keep the gun nozzle clean of spatter. Replace the contact tip if blocked or feeding poorly.

10. Keep the gun straight as possible when welding, to avoid poor wire feeding.

11. Use both hands to steady the gun when you weld. Do this whenever possible. (This also applies to Stick and TIG welding, and plasma cutting.)

12. Keep wire feeder hub tension and drive roll pressure just tight enough to feed wire, but don’t overtighten.

13. Keep wire in a clean, dry place when not welding, to avoid picking up contaminants that lead to poor welds.

14. Use DCEP (reverse polarity) on the power source (on solid wire).

15. A drag or pull gun technique will give you a bit more penetration and a narrower bead. A push gun technique will give you a bit less penetration, and a wider bead. (Refer to Diagram 3).

Modes of MIG (GMAW) Transfer
The term modes of transfer is used to describe the process by which the wire electrode is melted and deposited into the puddle. The most common way to classify metal transfer is according to the size, frequency, and characteristics of the metal drops being transferred. There are three modes of metal transfer that we will discuss here:
• Short Circuit Transfer
• Globular Transfer
• Spray Transfer
The stability of the welding arc and the metallurgical changes in the electrode wire are dependent on the mode of transfer. Welding procedures are categorized according to the mode of transfer

Short Circuit Transfer (SCMT)
Short circuit transfer gets its name from the welding wire actually “short circuiting” (touching) the base metal many times per second. When the welding gun trigger is pressed, the electrode wire feeds continuously from the wire feeder, through the gun, and to the arc area, shortcircuiting to the base metal, exploding and establishing an arc. While welding, this cycle can repeat itself between 20 and as much as 250 times per second.

Globular Transfer
A globular transfer for GMAW is often referred to as the state of transfer between short-circuiting and spray arc transfer. Large “globs” of weld metal transfer across the arc in a gravity transfer. The droplets are usually larger than the electrode wire. Although the electrode wire is pinched off at the arc, globular transfer does not achieve a true spray transfer. Globular is a more unstable transfer, with a less smooth weld bead appearance. Globular transfer can, in many cases, yield more spatter. Since spatter is waste, it is not a desirable side effect of globular transfer. Globular transfer can also cause cold lapping or incomplete fusion due to the large metal droplets splashing metal out of the puddle.

Spray Transfer
A spray transfer “sprays” a stream of tiny molten droplets across the arc, from the electrode wire to the base metal. These molten droplets are usually smaller than the diameter of the unmelted electrode wire. The arc is said to be “on” all of the time, once an arc is established. The spray transfer uses relatively high voltage (24 volts or higher depending upon the type of shielding gas), wire feed speed and amperage values, compared to short circuit transfer. Because of the high voltage, wire feed speed and amperage, there is a resulting high current density. The high current density produces high metal deposition rates. The high degree of heat in the spray arc weld puddle makes for a larger weld puddle that is more fluid than the weld puddle for short circuit transfer. Because of this heat and the size of the weld puddle, spray transfer is somewhat limited in welding positions. The heat and size of the weld puddle also limits spray transfer to material 1/8” or thicker. Welding steel with spray transfer is usually done in the flat position, and the horizontal fillet weldposition. Horizontal position spray arc welds are lap and T- joint fillet welds.