GMAW Principles SECTION OVERVIEW: These slides are meant to lead into the discussion on the components involved with GMAW welding. TEACHER NOTES: Slides 8-16: When using these slides, discussion could include: With semi-automatic MIG welding, the electrode wire is fed through a welding gun controlled by the operator. The operator starts the arc and controls the puddle. In automatic MIG welding, a robot or automated machine makes the weld. An arc digs into the base metal much like water from a nozzle on a garden hose digs into the earth. (The flow of the water is like welding current and water pressure is similar to voltage) Molten metal forms a molten pool or crater and tends to flow away from the arc while cooling and solidifying. A continuous even flow of shielding gas is needed to protect the molten weld metal from atmospheric contaminants such as oxygen and nitrogen. The shielding gas comes from a gas cylinder and flows through the gun and cable assembly, through the gas nozzle, and into the welding zone.

GMAW is the most widely used arc welding process in the United States GMAW Definition GMAW stands for Gas Metal Arc Welding A solid metal wire is fed through a welding gun and becomes the filler material Shielding gas is used to protect the molten puddle from the atmosphere which results in a weld without slag GMAW is the most widely used arc welding process in the United States

GMAW Circuit Three things happen when the GMAW gun trigger is pulled: The wire electrode begins to feed The circuit becomes electrically ‘hot’ Completes the circuit

GMAW Components Let’s look a little closer at the GMAW process 4 5 2 1 Travel direction Generally, drag on thin sheet metal and push on thicker materials Shielding Gas 4 Solidified Weld Metal Electrode 5 2 Arc 1 3 Weld Puddle

1 - Electrode A GMAW electrode is: A metal wire Measured by its diameter GMAW electrodes are commonly packaged on spools, reels and coils ranging from 1lb to 1000lbs

2 - Arc An electric arc occurs in the gas filled space between the electrode wire and the work piece Electric arcs can generate temperatures up to 10,000°F

This is what the welder watches and manipulates while welding 3 - Weld Puddle As the wire electrode and work piece heat up and melt, they form a pool of molten material called a weld puddle This is what the welder watches and manipulates while welding .045” ER70S-6 at 400 ipm wire feed speed and 28.5 Volts with a 90% Argon/ 10% CO2 shielding gas

GMAW welding requires a shielding gas to protect the weld puddle Shielding gas is usually CO2, argon, or a mixture of both The gauges on the regulator show gas flow rate and bottle pressure

5 - Solidified Weld Metal The welder “lays a bead” of molten metal that quickly solidifies into a weld The resulting weld is slag free An aluminum weld done with the GMAW process

Application Activity SECTION OVERVIEW: This slide reviews what has been learned about the GMAW process. TEACHER NOTES: (Explanation of Activity) Slide 17-18: After having discussed the parts included on this slide, students will take a quiz as an application activity. For the activity, have participants work individually and mark 1-5 on a piece of paper. Explain that this activity is meant to check student understanding of GMAW before beginning to apply the process in the lab. Project slide on the screen and have each student fill in the blanks on a piece of paper to be turned in. Collect papers and discuss. Answers to the Application Activity are: 1. Electrode 2. Arc 3. Weld Puddle 4. Shielding Gas 5. Solidified Weld Metal

GMAW Components Application Activity Let’s review the GMAW process 1 __________ 2 __________ 3 __________ 4 __________ 5 __________ Travel direction Generally, drag on thin sheet metal and push on thicker materials 4 5 2 1 3

Striking an Arc and Making a Weld SECTION OVERVIEW: These slides discuss striking an arc and making a weld using the GMAW process. TEACHER NOTES: Slides 22-26: Teacher might want to discuss … Once the arc has been established, maintaining the correct contact tip to work distance (CTWD) becomes extremely important. The CTWD should be approximately 3/8 to ½ inch (10-12 mm) long. The easiest way to tell if CTWD is right length is to listen to the sound. If the CTWD is too short the wire electrode can fuse to the contact tip. It also causes the arc voltage to raise resulting in a flat bead shape, increase in spatter and possible undercut. If the CTWD is too long the electrode can stub out. It also causes the arc voltage to drop resulting in a ropey and convex bead, increase in spatter and possible loss of gas shielding.

Laying a Bead Maintain a Contact Tip to Work Distance (CTWD) of 3/8” to 1/2” Use a uniform travel speed Most Importantly – Watch the Puddle! The appearance of the puddle and ridge where molten metal solidifies indicates correct travel speed. The ridge should be approximately 3/8” (10 mm) behind the wire electrode. Most beginners tend to weld too fast resulting in a ropey bead which means SLOW down!

Fill the Crater Fill the crater by pausing or using a slight back step Release gun trigger and pull gun away from the work after the arc goes out Large craters can cause weld cracking Crater cracks cannot be tolerated on NASCAR radiators.