What is Welding? As Identified by the American Welding Society, a weld is a formed when separate pieces of material are Fused together through the application of Heat. The Heat must be high enough to cause the metal softening or melting of the pieces to be joined.

Weld Terminology The Weld Face is the exposed surface of the weld (top). Weld Penetration is indicated by the height of the exposed surface of the weld on the back side. Full Weld Penetration is needed to assume maximum weld strength.

Burn-Through Results from too much heat, which burns a hole through the back side of the metal. Porosity This occurs when there are tiny little holes that appear inside the weld. This is caused by welding with no gas or a clogged nozzle.

Weld Category (MIG) Metal Inert Gas is a Wire – Feed welding process commonly used in collision repair. Another name for this type of welding is called Gas Metal Arc Welding or (GMAW).

MIG Welding Process MIG welding uses a Small diamerter welding wire electrode that is automatically fed into the weld joint. The welding machine feeds the Wire out and through the Welding Gun. A Short arc is generated between the Base Metal and the Wire. The resulting heat from the arc Melts the welding wire and joins the metals. See Figure 9-8

During the welding process a Shielding Gas is used. This protects the weld from Atmosphere and prevents oxidation of the Base Metal.

MIG welder Parts 1.Power Supply- Converts wall outlets AC in DC. 2.Welding Gun - Feeds wire and gas into the arc when the trigger is pulled. 3.Weld Cable – Large wires that connect welding to the vehicle.

4. Electrode Wire- Small welding wire fed down through the center of the gun. 5. Wire Feeder – A mechanism for pushing wire through the gun and into the weld arc. 6. Shielding Gas – Inert gas that surrounds and protects molten metal in a weld.

7. Regulator – Pressure controlled device for setting gas pressure. 8. Weld Clamp – Ground cable for connecting welder to vehicle.

Welder Amperage Rating gives the maximum current flow through the weld joint. The Thickness of the metal being welded determines the Amperage needed. There are two settings on a welder Voltage (heat) and Wire speed (amperage).

Duty Cycle – Is how many minutes a welder can safely operate at a given amperage level continuously over ten minutes. If a machines duty cycle rating is 40% then it can run 4 out of 10 minutes continuously.

MIG Welding Gun delivers wire current and Shielding Gas to the weld site. Contact Tip – this transfers current to the welding wire as the wire travels through. It is usually made of Copper alloy. It’s inside diameter must match the Diameter of the electrode wire. This is usually stamped on the tip in millimeters. This tip must be changed when the inside of the hole becomes enlarged, this reduces current transfer efficiency.

Nozzle this protects the contact tip and directs the Shielding gas flow. It must be kept clean at all times, a dirty nozzle can cause holes (porosity) in the weld. Anti spatter compound This may help spatter from sticking to the nozzle.

MIG Shielding Gas MIG shielding gas protects the weld area from Oxygen, Nitrogen, and Hydrogen which cause porosity in the weld. The gas also blows dirt and Particles away. (see figure 9-11)

There are two types of shielding gas: 1.Active Gas- which combines with the weld to contribute to weld quality. 2.Inert Gas- which protects the weld but does not combine with the weld.

MIG electrode wire comes in rolls that mount inside the MIG welder (see figure 9-12). Rollers grasp and force the wire out of the gun, whenever the gun trigger is Pulled.

Different welding machines will have different recommendations. Generally.023 can be used on all thicknesses and is generally recommended for collision repair use. Flux Core Wire has its own flux contained in a tubular electrode and does not require shielding gas.

MIG Welding Variables Most welders used for collision repair are 220 volt. These are also welders that use standard 110 volt outlets. The higher the voltage welders are the more expensive but usually provide better weld quality. The operator has to control several variables when welding these include:

Heat Setting or voltage this determines the length of the Arc. The more voltage the longer the arc. The longer the arc, the Wider and Flatter the weld since the weld wire melts off in larger drops.

Too short of an arc results in a Pulsing sound. Changing the Wire speed and amperage mainly affects weld Bead, Penetration, Height, and Width. To get steady arc with a steady sound and correct penetration. Both the heat (voltage) and Wire speed (amperage) must be matched to each other. Always set the Heat first then the wire speed.

Travel Speed is how fast you move the gun across the work piece. The slower the travel speed, the deeper the weld penetration. The wider the weld, and more head height. Travel Direction refers to weather you Push or pull the welding gun along the work piece. Push welding means you aim or angle the gun ahead of the weld puddle. Pull welding the weld means you aim or angle the gun behind the weld puddle (see figure 9-16)

MIG Weld Types MIG weld includes the following : Tack Continuous Butt Plug

1.Tack Weld is a short bead used for set up of a permanent weld. 2.Continuous Weld is a single weld bead along the joint. It could either be one continues weld or a series of short welds.(also called bead) 3.Skip Welding produces a continuous weld by making short welds at different locations to prevent overheating of the metal.

4. Stitch Welding is a continuous weld in one location but with short pauses to prevent over heating. 5. Butt Weld are formed by fitting two pieces of metal with an insert in the back and a weld in the center. 6. Plug Weld is made through a hole punched or drilled in the top pieces. The hole is then filled with a weld nugget, start in the center of the hole then slowly make a circular motion.