MIG

About

A Miller Millermatic 252 MIG welding machine, of which there are two in the Brunsfield Center

MIG (Metal Inert Gas) welding, also known as GMAW (Gas Metal Arc Welding), is a type of arc welding process in which a continuous solid wire electrode is fed through a welding gun and into the weld pool. The process uses a shielding gas, typically a mix of argon and $\mathrm{C}\mathrm{O}{\phantom{A}}_2$to protect the weld from contaminants in the atmosphere. MIG welding is widely used for its ease of use, speed, and adaptability to various metals.

How it works

In MIG welding, an electric arc forms between the wire electrode and the metal workpiece, heating them and causing them to melt and fuse. A motorized system feeds the wire at a controlled speed, while gas flows through the same gun to shield the weld.

• Wire electrode: consumable, ER70S-6 for mild steel.
• Shielding gas: Ferroline C25, 75% argon / 25% CO₂ for steel.
• Voltage and wire speed: adjusted based on material thickness.

Metal Thickness	Voltage	Wire Speed (In/min)
1/2''	29.5	515
3/8''	26.0	475
1/4''	21.0	375
3/16''	18.4	265
1/8''	17.4	230
14ga.	16.5	190
18ga.	15.8	120

Equipment Setup

Key Components of a MIG setup

Before turning on the welding machine, make sure that all safety measures are being followed. In particular, make sure all the proper PPE is being worn, nothing flammable is in the welding area, and close the curtains to protect others outised the welding area.

A simple procedure can be followed to properly start up the MIG welders.

1. Passing gas  
   1. Molten metal will oxidize more rapidly due to the heat and ruin the integrity of the weld. Inert “shielding” gas prevents this
   2. The cylinders need to be opened when welding
   3. Never overtighten or over open the valve on the cylinder
   4. Small knob on side of regulator controls flow  
   5. Flow meter shows increase but not decrease in flow unless gas is released
   6. Purge gas line and adjust to 25cfh for MIG (marked line on MIG bottles)
   7. 25% co2 (ferroline c25) for MIG and 100% Argon for TIG
   8. Regulator will show how much gas is left in the cylinder
   9. If you run out of gas, ask a supervisor to change the bottle for you. DO NOT TRY TO CHANGE YOURSELF
2. All about the settings
   1. MIG machine only has two settings; wire feed speed and voltage
   2. Chart above is on the machine or the door of the cabinet
3. The insides  
   1. The MIG welder has a cover on the side that holds the filler wire  
   2. Students should ask a supervisor before changing the wire  
   3. Tension adjustment knob and lever system (don’t play with it)
4. The torch
   1. As you press the trigger on the torch the wire and gas feed out
   2. Clean spatter (about every 30 min) to prevent welding or notching nozzle
   3. Taking off the nozzle we can see the contact tip
5. Staying grounded
   1. The ground needs to be attached in order for the electrical current to pass from the torch to your workpiece then back to the machine (closed circuit)  
   2. MIG welding requires a very good ground therefore it is always better to clamp the ground clamp directly onto the workpiece if possible
   3. When clamping on the table, clamp as close to your workpiece as possible
6. Ready to weld
   1. Positioning your body so that you are comfortable will make a significant difference in weld quality
   2. Position yourself so you can see what you are doing  
   3. Warn others before welding to avoid flashburn (bright arc in eyes)
   4. Snip off excess wire, clear off the contact tip and nozzle
   5. No more than ½" stickout
   6. Do a “dry run” (trace your weld path with the torch) to make sure you can reach comfortably

Technique

• When MIG welding it is important to hold the torch a certain way in order to achieve the best results
  • When welding a t joint or lap joint, it is recommended to hold the torch at a 45deg angle to the joint and use approximately a 5 to 15deg lead angle (ie pointing backwards to direction of travel)
  • For flat or butt joints, hold the torch at 90deg to the surface and with 5-15deg lead angle
  • Some kind of elbow rest can come in handy here—use some scrap and make your own!

• Slow and smooth movements are best
  • Use two hands or rest your elbow/forearm on the table/rest to keep steady
  • Stay consistent!

• Use shadows and reflections as landmarks to help keep a straight line
  • Turn your helmet shade down a bit if you’re struggling to see

• Do a pattern that keeps the arc at the front of the puddle to get better heat penetration
  • Zig zags are always good
  • Welding right to left, do C’s like this: CCCCCCCCC so the point is ahead of the weld
  • Left to right do it the other way: >>>>>>>>>>>>
  • Loop di loops or figure 8’s