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GMAW (MIG Welding) SECTION OVERVIEW:

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Presentation on theme: "GMAW (MIG Welding) SECTION OVERVIEW:"— Presentation transcript:

1 GMAW (MIG Welding) SECTION OVERVIEW:
Section Overviews are provided on the introductory slides at the front of each topical area to explain the intended use for the slides included in the section. Slide numbers are included on the Section Overview slides for easy reference when preparing for delivery of the slide content. TEACHER NOTES: Teacher Notes are included on the Section Overview slides as a reference tool when making class preparations. Suggested Activities are included as ideas for teachers to use to help students gain practical experience with the welding content. However, these are designed to be supplemented by each teacher based on local program needs. Slides have been developed to incorporate content information regarding performance standards from the American Welding Society (AWS) and the National Academic Standards for English, Science, and Math. INDIVIDUAL LESSON NOTES ARE AVAILABLE IN LESSON PLAN FACILITATOR’S GUIDE GMAW (MIG Welding)

2 GMAW Unit Topics During this overview, we will discuss the following topics: Safety GMAW Basics Equipment Set-Up Welding Variables Process Advantages and Limitations AWS Connection National Academic Standards Connection SECTION OVERVIEW: This slide is meant to start generating conversation and thoughts about content to be covered in this lesson. TEACHER NOTES: Bulleted information on topical areas is provided to lead class discussion on areas which are to be covered in the training.

3 Unit Objectives Upon successful completion of the GMAW Unit of Study, you will have learned about: Properly protecting yourself and others while welding Setting up and operating GMAW equipment Striking and maintaining an arc Welding in four positions using various electrodes Weld Inspection The AWS electrode classification system Taking the next step to becoming a certified welder SECTION OVERVIEW: This slide is included to explain the objectives of this unit of study. TEACHER NOTES: Teachers could use this opportunity to give a high-level overview of the importance and application of GMAW welding in today’s society.

4 GMAW Safety SECTION OVERVIEW:
The next few slides are meant to point out safety requirements when using the GMAW process. TEACHER NOTES: Slides 4-7: Bulleted information on topical areas is provided to lead class discussion on important areas of safety to be practiced in the GMAW welding environment. To download your own copy of ‘Safety in Welding, Cutting and Allied Processes’ (ANSI Z49.1) go to: To download your own copy of Lincoln Electric’s Arc Welding Safety (E205) document go to: To order copies of Lincoln Electric’s Arc Welding Safety (E205) document and poster (E201) go to: (Quick Link: Literature Request) MSDS can be obtained from Lincoln Consumable packaging, online at (Quick Link: MSDS) or by calling For a free DVD on Welding Safely, submit order form in the back of the Lesson Plan Facilitator’s Guide (shipping and handling charges apply). See Facilitator’s Guide for more information on welding hazards such as Fumes and Gases and Electrical Shock.

5 GMAW Safety ‘GMAW Safety’ is supplemental and does not replace the information found in ‘Arc Welding Basics’ Understand and follow all safety precautions listed in ‘Safety in Welding, Cutting and Allied Processes’ (ANSI Z49.1), and Arc Welding Safety (E205) Understand and follow all warning labels found: On welding equipment With all consumable packaging Within instruction manuals Read Material Safety Data Sheets (MSDS) If you ever have a question about your safety or those around you, PLEASE ASK YOUR INSTRUCTOR!

6 GMAW Safety Fumes and Gases can be dangerous
Keep your head out of the fumes Use enough ventilation, exhaust at the arc, or both, to keep fumes and gases from your breathing zone and the general area Local exhaust and mechanical ventilation can be used without reducing weld quality Electric Shock can kill – to receive a shock your body must touch the electrode and work or ground at the same time Do not touch the electrode or metal parts of the electrode holder with skin or wet clothing Keep dry insulation between your body and the metal being welded or ground The coil of wire is ‘electrically hot’ when the trigger is pulled Arc Rays can injure eyes and skin -Choose correct filter shade (See chart below) ** Information taken from ANSI Z49.1:2005**

7 GMAW Safety REMEMBER – Gas Cylinders require SPECIAL safety precautions Cylinders must be secured in an upright position Cylinders should be located in an area away from arc welding, cutting, heat, sparks, and flame Refer to ‘Safety in Welding, Cutting, and Allied Processes’ (ANSI Z49.1) or Arc Welding Safety (E205) for more information on the handling of gas cylinders

8 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.

9 GMAW is the most widely used arc welding process in the United States
GMAW Definition GMAW stands for Gas Metal Arc Welding GMAW is commonly referred to as MIG or Metal Inert Gas welding During the GMAW process, a solid metal wire is fed through a welding gun and becomes the filler material Instead of a flux, a 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

10 GMAW Circuit Three things happen when the GMAW gun trigger is pulled:
The wire electrode begins to feed The circuit becomes electrically ‘hot’ Current flows from the power source through the gun cable, gun, contact tip to the wire and across the arc. On the other side of the arc, current flows through the base metal to the work cable and back to the power source Shielding gas flows through the gun and out the nozzle

11 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

12 1 - Electrode A GMAW electrode is: A metal wire
Fed through the gun by the wire feeder Measured by its diameter GMAW electrodes are commonly packaged on spools, reels and coils ranging from 1lb to 1000lbs

13 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

14 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

15 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

16 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

17 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

18 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

19 Equipment Set Up SECTION OVERVIEW:
These slides explain how to set-up the equipment for GMAW and covers process variables. TEACHER NOTES: Slides 19-21: For welding procedure recommendations see: The Lesson Plan Facilitator’s Guide Lincoln Electric’s GMAW Welding Guide - The inside of a Lincoln Electric combination wire feeder/ welder. Check the gas nozzle. Turn the gas supply on. If adjustable, set for cubic feet per hour (7 to 10 l/min.) under normal conditions increasing to as high as 35 CFH (17 l/min) in drafty and/or slightly windy conditions. The liner and contact tip should match that of the electrode diameter being used. The work clamp must be grounded to the work piece. Be sure to make a good connection.

20 GMAW Equipment Set Up Connect work clamp Select electrode a. Type
b. Diameter 3. Select shielding gas 4. Turn power supply on 5. Adjust machine output a. Wire feed speed b. Voltage 6. Adjust gas flow rate Why would GMAW be a better choice than SMAW for this job?

21 GMAW Process Variables
Welding variables Wire Feed Speed (WFS) Voltage Operator controlled variables Travel speed Gun angles Contact tip to work distance (CTWD) Gas flow rate What is the relationship between WFS and amperage?

22 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.

23 Position the gun over joint
Striking an Arc Position the gun over joint Position the face shield to protect eyes and face Pull the gun trigger and begin welding What are some things to consider before striking an arc?

24 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!

25 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.

26 Restarting a Bead Restart the weld bead by back stepping into the last weld’s crater and then continue moving forward This technique should result in a seamless transition from one weld to the next 1 2 Back step

27 Modes of Metal Transfer
SECTION OVERVIEW: These slides discuss two conventional modes of metal transfer: short arc and spray arc TEACHER NOTES: Slides 27-31: Short Arc Transfer The wire shorts to the base material, the molten metal is pinched off and transferred to the weld puddle. Common gas mixtures for short arc: 100% CO2 or 75% Argon/ 25% CO2 Typical applications include thin materials, out of position welding, joints with poor fit up, root pass on pipe and when using 110V welders. Axial Spray Arc Transfer Very high currents are used in axial spray arc transfer (or spray arc). The current level must be above the transition level and the shielding gas must contain at least 80% Argon. A point forms at the end of the electrode and fine droplets of molten metal ‘spray’ across the arc. The droplets are equal to or smaller than the electrode diameter and are directed axially in a straight line to the weld puddle. Typical applications include thick materials, flat and horizontal welding, structural fabrication, heavy machinery and aluminum welding. For more information on the conventional modes of metal transfer see the GMAW Lesson Plan Facilitator’s Guide and Lincoln Electric’s free GMAW Welding Guide (http://content.lincolnelectric.com/pdfs/products/literature/c4200.pdf)

28 Modes of Metal Transfer
GMAW is a process that features several distinctive, individual methods and types of metal transfer The mode of metal transfer is determined by a number of welding variables Voltage Amperage Shielding Gas By changing one or more variables, you can go from one metal transfer mode to another

29 Modes of Metal Transfer
Two common conventional modes of metal transfer are: Short arc Axial spray arc The application, joint design, base material thickness, and properties determine the appropriate mode to use Typical short arc application Typical axial spray arc application

30 Short Arc Transfer In short arc transfer…
The arc is initiated and a droplet is formed on the end of the wire The wire touches the work piece and produces a short circuit The droplet is then transferred to the weld puddle

31 Axial Spray Arc Transfer
In axial spray arc transfer … Very high currents are used A point forms at the end of the electrode and the fine droplets The puddle is very fluid making out of position welding difficult

32 Troubleshooting Welds
SECTION OVERVIEW: The next slide explains about troubleshooting welds. TEACHER NOTES: Slide 32-33: Corrective actions for common GMAW problems: Porosity Check for proper gas flow/ block any winds or drafts Clean joints from moisture, paint, etc. Check for proper WFS and Voltage settings Decrease CTWD, drag angle, and travel speed Ropey and Convex Check or reset WFS & Volts (increase voltage first) Decrease CTWD, travel speed, and drag angle (push angle) Excessive Spatter Check and reset WFS and Volts Increase drag angle Decrease CTWD and travel speed Eliminate Stubbing Check or rest WFS & Volts (increase voltage first) Decrease CTWD

33 Troubleshooting Welds
GOAL - Make Good Welds Eliminate Porosity Eliminate Ropey Convex bead Eliminate Excessive Spatter

34 Advantages and Limitations
SECTION OVERVIEW: This section is meant to lead into a discussion regarding the advantages and limitations of the GMAW welding process. TEACHER NOTES: Slides 34-36: Advantages High operating factor: The welder does not have to stop and clean slag or change electrodes. Easy to learn: GMAW is easier to learn than Stick welding Clean process with little or no slag and spatter - High efficiency (93-98%) Welds can be made on a wide variety of metals and alloys. Can be done in all welding positions Disadvantages: Less portable – Gun lengths are often only 15 feet long. More expensive due to higher equipment price than SMAW and the need for a gas bottle. Shielding gas can be blown away by winds so GMAW may require special precautions when welding outdoors or in drafty areas. In spray arc transfer - the process radiates a lot of heat Difficult to use in out of position joints For more information on GMAW consumables and gases, see the Lesson Plan Facilitator’s Guide or GMAW Welding Guide available through Lincoln Electric

35 Advantages of GMAW High operating factor Easy to learn Limited cleanup
Use on many different metals: stainless steel, mild (carbon) steel, aluminum and more All position Great for home use with 115V and 230V units

36 Limitations of GMAW Less portable with shorter gun lengths (15 foot guns) GMAW equipment is more expensive than SMAW equipment External shielding gas can be blown away by winds High radiated heat Difficult to use in out of position joints

37 AWS Classification of GMAW Electrodes
SECTION OVERVIEW: This section is meant to lead into a discussion about the AWS Classification of GMAW Electrodes TEACHER NOTES: Slides 37-38 For more information on the AWS classification of GMAW electrodes see Lincoln Electric’s free ‘GMAW Welding Guide’ -

38 AWS Classification of GMAW Electrodes
ER70S-X Electrode Rod 70,000 psi Min. Tensile Strength Solid Chemistry, Amount of Deoxidizers (Silicon, Manganese and/or Aluminum, Zirconium and Titanium) X=2,3,4,6,7 or G


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