Work Clamp

First of all we’ll talk about a few things that you need to know when welding on a vehicle.  You always want to keep the work clamp close to where you are welding on the vehicle.  For example, you certainly wouldn’t want have the work clamp on the back bumper and be welding on the front section!  Try to keep the work clamp just as close to you as possible. Another thing you want to do when welding on a car is to disconnect the battery.  Anytime you have the welding on the car, you are making circuit and you don’t want have your battery connected, as this could damage electrical components on the car.   Disconnect the battery by disconnecting the negative cable.  Then isolate the negative battery cable by wrapping it with a rag or plastic to eliminate the cable accidently grounding itself to the car.

Computer Components

Another consideration when working on cars is the computer components.  If they were within 12 inches from the area you are welding, you really need to remove those components to prevent damaging them when welding.

Cover Glass

Before welding, cover glass or anything else that can become damaged during welding process with a fire blanket or spark resistant paper.  Even grinding can pit the glass so keep the glass covered with welding blankets or some type of protective sheeting until the repairs have been completed.

Advantages

The advantage of MIG welding over Oxy/Settling welding is less of a heat zone.  It does not heat the metal as much as a Oxy/Acetylene torch does.  

Skill Level

MIG welding requires less skills that arc, oxy/acetylene, or TIG welding and is a fast and effective welding process.

Polarity

MIG welders have two different polarities. You have a reverse polarity, which is use in auto body work.  This is where the electrode that the wire is coming out of is the positive and the work clamp is your negative.  This setting uses welding wire and a shielding gas.  The other type is straight plurality, which is used with flux cored wire.  This setting required and flux core wire, but no shielding gas is needed.  Flux core wire in not recommended for thinner sheet metals and is not used in auto body repair.  You need to be certain the welder is set on the correct polarity setting for the type of welding you will be performing. 

Short Circuit Transfer

There are different types of welding that can be performed with a MIG welder, but we are going to focus on the short circuit transfer, as this works best thinner sheet metals.  When welding, the wire the electrodes coming out hit the metal being welded which make a circuit.  When the circuit is made it shorts out.  This happens about 90 to 230 times per second when using .023 welding wire as use for welding thin metals.  As mentioned the wire diameter recommended is .023 and they wire type recommended is ER70S-6 and the ER stands for electrode wire, the 70 is the tensile strength, it is to about 70,000, and the S2 stands for solid wire.  The ‘6’ is the chemical making of the wire that you are using.

Shielding Gas

Whenever using solid wire you will need a shielding gas. You can use CO2 straight for some of the thicker metals but in auto body a mixture of 75% argon, 25% CO2 is recommended and provides the smoothest weld for the thinner metals.

Shielding gas helps protect the weld, keeps the oxygen out and it helps to create a nice clean weld. Without the shielding gas the weld is going to have a lot of pin holes, called porosity and is not going to have good penetration.

The shielding gas should be set anywhere from 20 to 30 psi at the regulator.  20 psi works well for indoors, such as a body shop or garage.  

First, the wire feeds through the liner from the welding machine.  Then the wire feeds through the gun, and through the tip, which is attached to the end of the gun.  The liner is covered with a hose, which provides a path for the shielding gas to pass though.  At the end of the gun, a nozzle covers the tip and directs the shielding gas to the surface being welded. 

This is a basic overview of a MIG welder, next we will discuss the different types of welds performed in auto body repair.