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 GUIDEGMAW(MIG Welding)
2 GMAW Unit TopicsDuring this overview, we will discuss the following topics:SafetyGMAW BasicsEquipment Set-UpWelding VariablesProcess Advantages and LimitationsAWS ConnectionNational Academic Standards ConnectionSECTION 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 ObjectivesUpon successful completion of the GMAW Unit of Study, you will have learned about:Properly protecting yourself and others while weldingSetting up and operating GMAW equipmentStriking and maintaining an arcWelding in four positions using various electrodesWeld InspectionThe AWS electrode classification systemTaking the next step to becoming a certified welderSECTION 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 callingFor 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 equipmentWith all consumable packagingWithin instruction manualsRead 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 fumesUse enough ventilation, exhaust at the arc, or both, to keep fumes and gases from your breathing zone and the general areaLocal exhaust and mechanical ventilation can be used without reducing weld qualityElectric Shock can kill – to receive a shock your body must touch the electrode and work or ground at the same timeDo not touch the electrode or metal parts of the electrode holder with skin or wet clothingKeep dry insulation between your body and the metal being welded or groundThe coil of wire is ‘electrically hot’ when the trigger is pulledArc Rays can injure eyes and skin -Choose correct filter shade (See chart below)** Information taken from ANSI Z49.1:2005**
7 GMAW SafetyREMEMBER – Gas Cylinders require SPECIAL safety precautionsCylinders must be secured in an upright positionCylinders should be located in an area away from arc welding, cutting, heat, sparks, and flameRefer 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 DefinitionGMAW stands for Gas Metal Arc WeldingGMAW is commonly referred to as MIG or Metal Inert Gas weldingDuring the GMAW process, a solid metal wire is fed through a welding gun and becomes the filler materialInstead of a flux, a shielding gas is used to protect the molten puddle from the atmosphere which results in a weld without slagGMAW 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 feedThe 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 sourceShielding 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 directionGenerally, drag on thin sheet metal and push on thicker materialsShielding Gas4Solidified Weld MetalElectrode52Arc13Weld Puddle
12 1 - Electrode A GMAW electrode is: A metal wire Fed through the gun by the wire feederMeasured by its diameterGMAW electrodes are commonly packaged on spools, reels and coils ranging from 1lb to 1000lbs
13 2 - ArcAn electric arc occurs in the gas filled space between the electrode wire and the work pieceElectric arcs can generate temperatures up to 10,000°F
14 This is what the welder watches and manipulates while welding 3 - Weld PuddleAs the wire electrode and work piece heat up and melt, they form a pool of molten material called a weld puddleThis 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 bothThe 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 weldThe resulting weld is slag freeAn 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. Electrode2. Arc3. Weld Puddle4. Shielding Gas5. Solidified Weld Metal
18 GMAW Components Application Activity Let’s review the GMAW process1 __________2 __________3 __________4 __________5 __________Travel directionGenerally, drag on thin sheet metal and push on thicker materials45213
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 GuideLincoln 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. Diameter3. Select shielding gas4. Turn power supply on5. Adjust machine outputa. Wire feed speedb. Voltage6. Adjust gas flow rateWhy would GMAW be a better choice than SMAW for this job?
21 GMAW Process Variables Welding variablesWire Feed Speed (WFS)VoltageOperator controlled variablesTravel speedGun anglesContact tip to work distance (CTWD)Gas flow rateWhat 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 ArcPosition the gun over jointPosition the face shield to protect eyes and facePull the gun trigger and begin weldingWhat are some things to consider before striking an arc?
24 Laying a BeadMaintain a Contact Tip to Work Distance (CTWD) of 3/8” to 1/2”Use a uniform travel speedMost 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 outLarge craters can cause weld crackingCrater cracks cannot be tolerated on NASCAR radiators.
26 Restarting a BeadRestart the weld bead by back stepping into the last weld’s crater and then continue moving forwardThis technique should result in a seamless transition from one weld to the next12 Back step
27 Modes of Metal Transfer SECTION OVERVIEW:These slides discuss two conventional modes of metal transfer: short arc and spray arcTEACHER NOTES:Slides 27-31:Short Arc TransferThe 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% CO2Typical 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 TransferVery 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 (
28 Modes of Metal Transfer GMAW is a process that features several distinctive, individual methods and types of metal transferThe mode of metal transfer is determined by a number of welding variablesVoltageAmperageShielding GasBy 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 arcAxial spray arcThe application, joint design, base material thickness, and properties determine the appropriate mode to useTypical short arc applicationTypical 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 wireThe wire touches the work piece and produces a short circuitThe droplet is then transferred to the weld puddle
31 Axial Spray Arc Transfer In axial spray arc transfer …Very high currents are usedA point forms at the end of the electrode and the fine dropletsThe 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:PorosityCheck for proper gas flow/ block any winds or draftsClean joints from moisture, paint, etc.Check for proper WFS and Voltage settingsDecrease CTWD, drag angle, and travel speedRopey and ConvexCheck or reset WFS & Volts (increase voltage first)Decrease CTWD, travel speed, and drag angle (push angle)Excessive SpatterCheck and reset WFS and VoltsIncrease drag angleDecrease CTWD and travel speedEliminate StubbingCheck or rest WFS & Volts (increase voltage first)Decrease CTWD
33 Troubleshooting Welds GOAL - Make Good WeldsEliminate PorosityEliminate Ropey Convex beadEliminate 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:AdvantagesHigh 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 weldingClean 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 positionsDisadvantages: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 heatDifficult to use in out of position jointsFor 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 moreAll positionGreat for home use with 115V and 230V units
36 Limitations of GMAWLess portable with shorter gun lengths (15 foot guns)GMAW equipment is more expensive than SMAW equipmentExternal shielding gas can be blown away by windsHigh radiated heatDifficult 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 ElectrodesTEACHER NOTES:Slides 37-38For more information on the AWS classification of GMAW electrodes see Lincoln Electric’s free ‘GMAW Welding Guide’ -
38 AWS Classification of GMAW Electrodes ER70S-XElectrodeRod70,000 psi Min. Tensile StrengthSolidChemistry, Amount of Deoxidizers (Silicon, Manganese and/or Aluminum, Zirconium and Titanium) X=2,3,4,6,7 or G