Welding is the process of joining metal together structurally. For a fantastic instructable that is a very in-depth look at the theory, details and safety about MIG welding, read noahw's How to Weld - MIG Welding.
This instructable is focused on the steps to perform regarding the equipment for welding. It assumes that the machine has enough air, the wire is threaded and that all safety is accounted for. It also assumes you have set up your components to weld.
I made this at TechShop Detroit (www.techshop.ws).
Step 1: Move Fume Extractor Over Welding Area
Move the fume extractor, if available, over your welding area and turn on. It will automatically start when it detects fumes to extract. There is also a light that can be independently used.
Step 2: Attach Ground Clamp
The ground clamp is required and can be attached to any metal surface that can provide an adequate ground. In this case, the welding setup table is used.
Step 3: Ensure Adjusting Screw Is Loose
The gas cylinder connected to the welding unit has the following general appearance. The adjusting screw is labeled in the picture.
Step 4: Open Cylinder Using Handwheel
Open the cylinder handwheel ensuring that your hand is around the wheel and not above it. This is in case there is a deficiency and the components are released under high pressure. As well, ensure that you are standing opposite the regulator apparatus.
When you fully open the cylinder handwheel you will notice that the cylinder pressure gauge changes from 0 to a value, the maximum of which is 2500 PSI. In this case the pressure is a little over 1000 PSI, enough to weld.
Step 5: Turn Adjusting Screw
Gently turn the adjusting screw clockwise until the needle on the gauge reaches 10-15 CFH.
Step 6: Determine Welding Settings
In this case the welding settings are in a panel to the side of the welding unit. The chart is to be used to determine the Voltage and wire speed.
In this particular unit, the critical setup to know is that the wire size is .035 in.
The gas composition can be viewed on the cylinder - 75% Ar / 25% CO2.
The thickness of the material (ga) you are welding is the last parameter you need to determine the Voltage and wire speed.
Step 7: Turn on Welder
Once you know the settings to apply and have a safe area, turn on the welder using the switch circled in the image. Note, for this particular unit the slowest wire speed is 50 meaning that pulling the trigger on the gun will always feed the wire. This is important to note in case you have to release pressure, for example, you went above 15 CFH in Step 5.
Step 8: Adjust Wire Speed and Voltage
Using the chart we referenced in Step 6, adjust Wire Feed Speed and Volts to appropriate values. In this case, 18 ga material leads to 120 and 16 respectively.
Step 9: Ensure Welding Torch Has Appropriate Amount of Wire
The first image shows the appropriate amount of wire. If the wire is too long, just clip it until it is a reasonable length.
Step 10: Weld the Components
Weld away. Again, reference noahw's How to Weld - MIG Welding for techniques and links to further material.
Step 11: Turn Wire Feed to Lowest Setting
When you are finished, turn the wire speed to the lowest setting, in this case 50.
Step 12: Close Gas Cylinder Valve
Close the handwheel until it is tight.
Step 13: Bleed Regulator
Bleed the regulator by depressing trigger on gun until the CFH drops to the lowest level. Note that wire will feed since the lowest wire speed (50) is not 0.
Step 14: Unscrew Adjusting Screw
Unscrew adjusting screw until it is completely loose.
Step 15: Turn Off Welder
Turn the welding unit off using the ON/OFF switch.
Step 16: Remove Ground Clamp
Remove your ground clamp from the welding table.
Step 17: Coil Wires
Neatly coil all the wires.