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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

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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

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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

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GMAW Safety

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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: www.aws.org/technical/facts/Z49.1-2005-all.pdf

To download your own copy of Lincoln Electric’s Arc Welding Safety (E205) document go to: http://content.lincolnelectric.com/pdfs/products/literature/e205.pdf

To order copies of Lincoln Electric’s Arc Welding Safety (E205) document and poster (E201) go to: www.lincolnelectric.com (Quick Link: Literature Request)

MSDS can be obtained from Lincoln Consumable packaging, online at www.lincolnelectric.com (Quick Link: MSDS) or by calling 1-216-481-8100

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.

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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)

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If you ever have a question about your safety or those around you,

PLEASE ASK YOUR INSTRUCTOR!

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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)

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** Information taken from ANSI Z49.1:2005**

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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

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�GMAW Principles

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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.

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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

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GMAW is the most widely used arc welding process in the United States

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GMAW Circuit

Three things happen when the GMAW gun trigger is pulled:

The wire electrode begins to feed
The circuit becomes electrically ‘hot’

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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

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GMAW Components

Let’s look a little closer at the GMAW process

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Travel direction

Electrode

1

Arc

2

Weld Puddle

3

Shielding Gas

4

5

Solidified Weld Metal

Generally, drag on thin sheet metal and push on thicker materials

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1 - Electrode

A GMAW electrode is:

A metal wire
Fed through the gun by the wire feeder
Measured by its diameter

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GMAW electrodes are commonly packaged on spools, reels and coils ranging from 1lb to 1000lbs

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2 - Arc

An electric arc occurs in the gas filled space between the electrode wire and the work piece

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Electric arcs can generate temperatures up to 10,000°F

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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

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.045” ER70S-6 at 400 ipm wire feed speed and 28.5 Volts with a 90% Argon/ 10% CO2 shielding gas

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4 - Shielding Gas

GMAW welding requires a shielding gas to protect the weld puddle
Shielding gas is usually CO2, argon, or a mixture of both

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The gauges on the regulator show gas flow rate and bottle pressure

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5 - Solidified Weld Metal

The welder “lays a bead” of molten metal that quickly solidifies into a weld
The resulting weld is slag free

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An aluminum weld done with the GMAW process

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Application Activity

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GMAW Components �Application Activity

1 __________

2 __________

3 __________

4 __________

5 __________

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Let’s review the GMAW process

Travel direction

1

2

3

4

5

Generally, drag on thin sheet metal and push on thicker materials

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Equipment Set Up

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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

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Why would GMAW be a better choice than SMAW for this job?

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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

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What is the relationship between WFS and amperage?

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Striking an Arc �and Making a Weld

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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.

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Striking an Arc

Position the gun over joint
Position the face shield to protect eyes and face
Pull the gun trigger and begin welding

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What are some things to consider before striking an arc?

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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!

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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!

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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

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Crater cracks cannot be tolerated on NASCAR radiators.

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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

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2 Back step

1

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Modes of Metal Transfer

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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)

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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

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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

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Typical short arc application

Typical axial spray arc application

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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

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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

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Troubleshooting Welds

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Troubleshooting Welds

GOAL - Make Good Welds

Eliminate Porosity

Eliminate Ropey Convex bead

Eliminate Excessive Spatter

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Advantages and Limitations

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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

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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

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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

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AWS Classification of �GMAW Electrodes

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AWS Classification of �GMAW Electrodes

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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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Lesson Plans

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GMAW Lesson #1

Objective: To run a stringer (straight) bead using short arc transfer and to fill the crater
Equipment:

Single Process - Constant Voltage Power Source & Wire Feeder

Power MIG 215 or Power MIG 255C

Multi-Process

Composite: Power MIG 350 MP
Combination: V-350/ LF-72 package

Material:

Mild Steel Plate – 3/16” or thicker

.035” SuperArc L-56 (ER70S-6)
100% CO2 or 25% CO2/ 75% Argon blend shielding gas

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GMAW Lesson #2

Objective: To make a fillet weld on a lap joint in the horizontal position (AWS position 2F)
Equipment:

Single Process - Constant Voltage Power Source & Wire Feeder

Power MIG 215 or Power MIG 255C

Multi-Process

Composite: Power MIG 350 MP
Combination: V-350/ LF-72 package

Material

Mild Steel Plate – 10 gauge
.035” SuperArc L-56 (ER70S-6)
100% CO2 or 25% CO2/ 75% Argon blend shielding gas

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2F

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GMAW Lesson #3

Objective: To make a fillet weld on a tee joint in the horizontal position

(AWS position 2F)

Equipment:

Single Process - Constant Voltage Power Source & Wire Feeder

Power MIG 215 or Power MIG 255C

Multi-Process –

Composite: Power MIG 350 MP
Combination: V-350/ LF-72 package

Material:

Mild Steel Plate – 10 gauge
.035” SuperArc L-56 (ER70S-6)
100% CO2 or 25% CO2/ 75% Argon blend shielding gas

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2F

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GMAW Lesson #4

Objective: To make a fillet weld on a lap joint in the vertical position welding down (AWS position 3FD)
Equipment:

Single Process - Constant Voltage Power Source & Wire Feeder

Power MIG 215 or Power MIG 255C

Multi-Process –

Composite: Power MIG 350 MP
Combination: V-350/ LF-72 package

Material:

Mild Steel Plate – 10 gauge
.035” SuperArc L-56 (ER70S-6)
100% CO2 or 25% CO2/ 75% Argon blend shielding gas

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3FD

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GMAW Lesson #5

Objective: To make a fillet weld on a tee joint in the vertical position welding down (AWS position 3FD)
Equipment:

Single Process - Constant Voltage Power Source & Wire Feeder

Power MIG 215 or Power MIG 255C

Multi-Process –

Composite: Power MIG 350 MP
Combination: V-350/ LF-72 package

Material:

Mild Steel Plate – 10 gauge
.035” SuperArc L-56 (ER70S-6)
100% CO2 or 25% CO2/ 75% Argon blend shielding gas

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3FD

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GMAW Lesson #6

Objective: To make a butt weld with a gap in the vertical position �welding down
Equipment:

Single Process - Constant Voltage Power Source & Wire Feeder

Power MIG 215 or Power MIG 255C

Multi-Process –

Composite: Power MIG 350 MP
Combination: V-350/ LF-72 package

Material:

Mild Steel Plate – 10 gauge
.035” SuperArc L-56 (ER70S-6)
100% CO2 or 25% CO2/ 75% Argon blend shielding gas

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3G

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GMAW Lesson #7

Objective: To make a fillet weld on a tee joint in the overhead position (AWS position 4F)
Equipment:

Single Process - Constant Voltage Power �Source & Wire Feeder

Power MIG 215 or Power MIG 255C

Multi-Process –

Composite: Power MIG 350 MP
Combination: V-350/ LF-72 package

Material:

Mild Steel Plate – 10 gauge
.035” SuperArc L-56 (ER70S-6)
100% CO2 or 25% CO2/ 75% Argon blend shielding gas

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4F

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GMAW Lesson #8

Objective: To make a three pass fillet weld on a tee

joint in the horizontal position (AWS position 2F)

Equipment:

Single Process - Constant Voltage Power Source �& Wire Feeder

Power MIG 215 or Power MIG 255C

Multi-Process –

Composite: Power MIG 350 MP
Combination: V-350/ LF-72 package

Material:

Mild Steel Plate – ¼”
.035” SuperArc L-56 (ER70S-6)
100% CO2 or 25% CO2/ 75% Argon blend shielding gas

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2F

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GMAW Lesson #9

Objective: To run a horizontal fillet weld on a tee joint using axial �spray transfer (AWS position 2F)
Equipment:

Single Process - Constant Voltage Power Source �& Wire Feeder

Power MIG 225C

Multi-Process –

Composite: Power MIG 350 MP
Combination: V-350/ LF-72 package Material:

Mild Steel Plate – ¼”
.045” SuperArc L-56 (ER70S-6)
90% Argon/ 10% CO2 blend shielding gas

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2F

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AWS Connection

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American Welding Society (AWS) Connection

The GMAW unit of study covered information related to the following AWS requirements for certification:

Setting up for GMAW operations on carbon steel
Operating GMAW equipment on carbon steel
Making GMAW fillet welds on carbon steel

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English, Math, and Science Connection

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National Academic Standards Crosswalk

This unit covered academic content listed in the National Academic Standards as follows:

NM-MEA.9-12.1: Understands measurable attributes of objects and the units, systems, and processes of measurement
NM-PROB.CONN.PK-12.3: Recognizes and applies mathematics in contexts outside of mathematics.
NS-PHYSICAL SCIENCE: (Understands) structure and property of matter
NS-PHYSICAL SCIENCE: (Understands) chemical reactions
NLA-STANDARD 3: Uses grammatical and mechanical conventions in written compositions
NLA-STANDARD 10: Understands the characteristics and components of the media

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