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Like an artisan using specialized tools, an instructor uses many instructional tools, including personal experience, to maximize learner comprehension. The instructional tools and resources used may vary depending on the facility, the equipment available, and the budget.

This instructional guide describes the value and intended use of each component of the Welding Skills training package. This guide also provides information about key elements that determine instructional program format, the instructional methods used by successful instructors, and detailed instructional plans that correspond to each chapter of the textbook.

examination, and weld discontinuities and defects.

This section also guides learners through the essentials of the welding procedure and welder performance qualification.

Section eight covers the essential concepts that welders need to know about welding technology in order to succeed in the welding industry, including welding metallurgy, the weldability of ferrous and nonferrous metals, distortion control, welding symbols, and welding codes and standards. The appendix contains many useful tables, charts, and other supplemental reference material.

Learner Resources Welding Skills includes interactive learner resources that facilitate learning of key concepts presented in the textbook. The Welding Skills Learner Resources are described below: • The interactive Quick Quizzes® contain 20 multiple choice questions per section and can be used as a study tool or integrated into classroom instruction.

• The Illustrated Glossary includes terms, definitions, and links to selected illustrations and media clips.

• The Flash Cards provide a convenient method of reviewing common welding terms and definitions.

Flash Cards also provide practice in interpreting standard AWS welding symbols.

• The Welding Resources include useful references to supplement the material covered in the textbook.

• The Media Library includes video clips and animations that illustrate and enhance the concepts presented in the textbook.

• The ATPeResources.com link provides access to online instructional resources that support continued learning.

The Welding Skills Learner Resources can be accessed via the QuickLinks or Quick Response (QR) codes printed in the textbook. See QuickLinks and QR Code Access.

THE WELDING SKILLS TRAINING PACKAGE The Welding Skills training package contains a variety of instructional and reference materials that can be used to optimize learning. Each component of the package has a function and can be used in a variety of ways to suit the needs of a course or training program.

Textbook Welding Skills is divided into eight sections (modules).

Section one provides a brief introduction to the major welding processes as well as an overview of the many employment opportunities a career in welding provides.

This is followed by in-depth coverage of welding safety based on ANSE/AWS Z49.1. The section also includes an introduction to joint design and welding terminology.

Sections two through five are devoted to OAW, SMAW, GTAW, and GMAW respectively. Each section covers equipment operating theory, welding procedures, and applications in detail. Section six covers FCAW, thermal cutting processes, pipe welding, and other welding and joining processes.

Section seven is devoted to weld evaluation and testing, including destructive testing, nondestructive  2015 by American Technical Publishers, Inc. All rights reserved

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INSTRUCTIONAL RESOURCES

Textbook • GMAW–Equipment (pp. 217 – 234) Learner Resources • Quick Quizzes® • Illustrated Glossary • Flash Cards • Media Library • ATPeResources.com

Workbook • GMAW–Equipment (pp. 65 – 68) Instructor Resources • Instructional Guide • Premium PowerPoint® Presentations • Image Library • Assessments • Answer Keys

INSTRUCTIONAL POINTS

Note: Premium PowerPoint® Presentations can be used to introduce, reinforce, and review key chapter concepts. All figures can be accessed from the Image Library. Internet Resources can be accessed at ATPeResources.com.

1. Describe gas metal arc welding (GMAW).

• Gas metal arc welding (GMAW) is an arc welding process that uses an arc between a continuous wire electrode and the weld pool. GMAW uses an external shielding gas or a combination of shielding gases supplied from an external source to protect the molten weld.* • A GMAW weld can be applied by the semiautomatic, mechanized, or automatic methods.

– When semiautomatic welding is used, the wire feed speed, voltage setting, and gas flow rate are preset, but the welding gun is manually operated.

– In mechanized GMAW, the welding operator sets the welding parameters and monitors the welding operation while a mechanical device controls the welding gun along the joint.

– In automatic GMAW, the welding parameters and welding gun movements are programmed into a computer, and all aspects of the process are controlled by the equipment, such as in a robotic cell in a manufacturing environment.

• GMAW allows higher deposition rates, faster travel speeds, and less electrode waste, and it is easier to use than manual welding processes like SMAW, GTAW and OAW.* Access the Media Library: GMAW–Welding Machine.

• The most common current selected for GMAW is direct current electrode positive (DCEP).

DCEP is the most efficient current because it produces deep penetration.

• DCEN should not be used for GMAW because weld penetration is shallow and wide, there is excessive spatter, and no surface cleaning occurs.

2. Describe types of power sources used for GMAW. • GMAW uses a direct current (DC) welding power source capable of producing constant voltage (CV). Unlike constant-current (CC) power sources that have a steep volt-ampere (V-A) curve, CV power sources have a gently sloping V-A curve. See Figure 19-1.

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76 Welding Skills Instructor Resources

• CV welding power sources for GMAW can be transformer-rectifiers or inverters.

• Welding power sources rated at 350 A with 100% duty cycles are adequate for most commercial applications.

• With CV power sources, welding current provides the energy necessary to melt the electrode wire. The higher the wire feed speed, the higher the welding current.

• Voltage is set in relation to wire feed speed and is affected by the type and diameter of the welding wire, the type of base metal, and the type of shielding gas.

• CV power sources are designed to maintain selected arc voltage. They will maintain this preset voltage even with changes in electrode extension. An increase in electrode extension results in a slight increase in voltage. The increase in electrode extension also increases the resistance in the wire, which results in a decrease in the welding current because less current is required to maintain the same arc length. Similarly, a decrease in electrode extension decreases voltage slightly. The decrease in electrode extension reduces the resistance in the wire and results in an increase in current.* See Figure 19-2.

• Electrode extension is the distance from the contact tip to the end of the welding wire.* 3. Describe welding guns and their use in GMAW. • In addition to a DC/CV welding power source, GMAW equipment includes a welding gun cable and gun assembly, a wire feeder, shielding gas, and a workpiece lead with a workpiece connection. See Figure 19-3.

• A welding gun cable conducts the welding wire, shielding gas, and welding current to the welding gun. The welding gun cable contains a separate gas line for shielding gas, a current conductor to energize the electrode, and a gun cable liner that serves as a conduit for the welding wire.* • Welding gun components include a handle with a conductor tube and trigger, a contact tip, a gas nozzle, a gas diffuser, and an insulator. See Figure 19-4.

• Welding guns are available with curved or straight conductor tubes. Curved conductor tubes are typically used for semiautomatic welding, while straight conductor tubes are used for mechanized and automatic applications. See Figure 19-5.

• The contact tip conducts current from the welding gun to the welding wire. Contact tips are available with different hole sizes. The diameter of the hole in the contact tip should match the diameter of the welding wire.* • The gas diffuser distributes shielding gas evenly around the welding wire and contact tip, and the gas nozzle directs the flow of shielding gas to the molten weld.* • Spatter buildup on the gas nozzle, contact tip, and gas diffuser can restrict the flow of shielding gas. These components should be checked and cleaned regularly.* • A worn, damaged, or oversized contact tip (contact tube) may cause problems with arc starting because of poor electrical contact.* • The hand-operated trigger on the welding gun energizes the welding wire, starts the flow of the shielding gas, and activates the wire feeder.

• The welding gun cable should be kept as straight as possible to prevent kinking or flattening of the liner, which could impede the welding wire.  2015 by American Technical Publishers, Inc. All rights reserved

Instructional Plan Chapter 19 — GMAW – Equipment 77

• A dirty gun cable liner can cause problems with burnback and bird nesting. To keep the gun cable liner clean, blow shop air through it before installing a new spool of electrode wire. A damaged liner can also cause burnback or bird nesting.* – Burnback is a condition that occurs when welding wire is restricted and fuses to the end of a contact tip.

– Bird nesting is a tangle of wire that forms in a wire feeder when welding wire is restricted in the liner or by a burnback condition.

• A semiautomatic welding gun allows the welder to manually control and direct welding wire to the joint.

• A semiautomatic welding gun generally has a curved conductor tube. The curved conductor tube is used for most welding positions and provides easy access to intricate joints and difficult-to-weld patterns.

• Semiautomatic welding guns can be air cooled or water cooled.

• Automatic welding guns have a design similar to semiautomatic welding guns, but the gun is usually mounted to a fixture directly below the wire feeder.

• Automatic welding guns are typically water-cooled because of the high currents and duty cycles at which they operate.

4. Explain how wire feeders work.

• A wire feeder automatically advances the welding wire from the wire spool, through the welding gun cable liner and welding gun, to the arc. See Figure 19-6.

• A wire feeder also supplies welding current to the welding gun cable and contains a solenoid that activates the flow of shielding gas. Most wire feeders have a speed control, a voltage control, a purge button, and a jog button. Wire feeders designed for high wire feed rates may also have a burnback control.

– The wire feed speed control adjusts the speed with which welding wire feeds into the arc.

– The voltage control allows the welder to set the optimum arc length.

– The purge button allows the welder to set the shielding gas flow rate without using the gun trigger.

– The jog button advances the welding wire without using the gun trigger.

– The burnback control prevents the welding wire from freezing to the base metal by maintaining the arc briefly after the trigger is released.

• The wire feed mechanism that drives the welding wire consists of a variable speed electric motor connected to drive rolls.

– Wire feeders for light-duty applications have two drive rolls.

– Wire feeders for industrial applications typically have four drive rolls.

• Drive rolls for GMAW are grooved, and the tension on the drive rolls can be adjusted.

Grooves can be U-shaped, V-shaped, or knurled depending on the type of welding wire.

U-shaped grooves are used with soft wire such as aluminum. V-shaped grooves are used with steel wires, and knurled grooves are used with metal cored and flux cored wires. See Figure 19-7.

Access the Media Library: Wire Feeder Drive Roll.

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• The drive rolls and the welding gun liner must be properly sized to match the diameter of the welding wire. The wire outlet guide must be aligned closely with the groove in the drive rolls without touching it. See Figure 19-8.

• A wire feeder can be a push type, a pull type, or a push-pull type, depending on the location of the drive rolls.

– A push type wire feeder has drive rolls that push the welding wire through the gun cable liner to the welding gun.

– In the pull type wire feeder, the welding wire is fed through the liner and pulled by drive rolls located on the welding gun.

– The push-pull type wire feeder is used for driving welding wire long distances and for low-strength welding wires.

5. Identify common types of shielding gas used for GMAW. • The effects of oxygen, nitrogen, and hydrogen on a weld make it essential that they be excluded from weld areas during welding.

• Atmospheric gases can be excluded by using an inert gas for shielding. Argon and helium are inert gases that are commonly used for shielding. See Figure 19-9.

• Different shielding gases produce different weld bead contour and penetration characteristics. See Figure 19-10.

• Because of the oxidizing characteristic of CO2 gas, welding wires used with CO2 must contain deoxidizing elements.

• CO2 is the least expensive shielding gas and produces a wide, deep-penetrating weld bead.

A drawback of using CO2 for shielding is that it produces a somewhat violent arc. This can cause excessive spatter.

• Straight argon is seldom used as a shielding gas except when welding metals such as aluminum, copper, nickel, and titanium. Argon is often mixed with other gases to improve their stability.

• Helium has a higher ionization potential than argon, which allows for higher arc voltage.

It produces a deep, broad, parabolic weld with a low bead profile. Because of its high cost, helium is used primarily for special welding tasks and for nonferrous metals such as aluminum, magnesium, and copper.

• Argon-helium mixtures are commonly used for welding aluminum greater than 1″ thick, and on stainless steel.

• Oxygen is added to argon when welding mild steel to improve bead contour and penetration. A small amount of oxygen (up to 5%) improves penetration by broadening the deep penetration finger at the center of the weld bead.

• A mixture of 75% Ar and 25% CO2 is commonly used for welding mild and low-alloy steels with short-circuiting transfer. A 75/25 mixture produces shallower penetration, faster travel speeds, a smoother and more focused arc, and less spatter than 100% CO2, making it ideal for autobody applications.* • An argon-helium-CO2 mixture is used for applications where a high-crowned weld is detrimental.

• For most welding operations, the gas flow rate is approximately 20 cfh to 35 cfh. Insufficient shielding gas flow can cause porosity by allowing air to come into contact with the molten weld pool.*  2015 by American Technical Publishers, Inc. All rights reserved

Instructional Plan Chapter 19 — GMAW – Equipment 79

6. Identify considerations in selecting GMAW welding wire.

• Welding wire for GMAW should be similar in composition to the base metal.

• The copper coating on GMAW electrode wire aids in arc starting, improves wire feeding, and prolongs contact tip life.* • The AWS classifies welding wire for GMAW using an alpha-numeric designation.* See Figure 19-12.

– The E stands for electrode.* – The R stands for rod and indicates that it can be used as a non-current-carrying filler rod, as in GTAW.* – The number specifies the tensile strength of the deposited weld in thousands of pounds per square inch, for example, 70 = 70,000 psi.* – The S indicates a solid wire. The letter C in this same position would indicate composite (metal cored) wire.* – The digit following the dash indicates the chemical composition of the welding wire.* • Using this system enables a welder to choose the correct steel welding wire base on AWS specifications. See Figure 19-13.

• Generally, welding wire of 0.023″, 0.030″, or 0.035″ is best for welding thin metal, although it can be used to weld low- and medium-carbon steel and medium-thickness, high-strength/ low-alloy (HSLA) steel.

• Medium-thickness metal normally requires 0.045″ or Z\zn″ diameter welding wire. See Figure 19-14.

• Metal cored welding wires are often preferred to solid wires for high-production GMAW applications because they allow travel speeds 30% faster than solid wire.

• Metal cored welding wires are composite electrode wires consisting of a metal sheath filled with metallic powders.

• Metal cored wires handle contaminants such as rust and mill scale (a surface layer of ferrous oxide) well and bridge gaps due to poor fit-up without excessive melt-through. They can also be used to weld single and multiple-pass welds.

• Metal cored welding wires can be used to weld a variety of metal thicknesses, including thin-gauge metal used in automobile exhaust systems.

• Metal cored welding wires have replaced flux cored wires in some environments because they produce less smoke and fumes and require no post-weld cleaning.

REVIEW

 Review comprehension of chapter content using the following resources: • Textbook  Questions for Study and Discussion (p. 234) • Learner Resources  Quick Quiz®: Section 5— Gas Metal Arc Welding (GMAW)  Flash Cards: Terms and Definitions  Gas Metal Arc Welding (GMAW)/Flux Cored Arc Welding (FCAW) © 2015 American Technical Publishers, Inc. All rights reserved

80 Welding Skills Instructor Resources

 Media Library  GMAW–Welding Machine  Wire Feeder Drive Roll • Workbook  Chapter 19 Review Questions (pp. 65 – 68) • Answer Key  Textbook: Questions for Study and Discussion Chapter 19  Workbook: Review Questions for Chapter 19 EVALUATION

 Evaluate comprehension of chapter content using the following resource: • Instructor Resources  Assessments: Chapter 19 Test (generated from Test Banks) AWS SENSE-RELATED CONTENT

• Gas metal arc welding (GMAW) is an arc welding process that uses an arc between a continuous wire electrode and the weld pool. GMAW uses an external shielding gas or a combination of shielding gases supplied from an external source to protect the molten weld. (p. 217) • GMAW allows higher deposition rates, faster travel speeds, and less electrode waste, and it is easier to use than manual welding processes like SMAW, GTAW and OAW. (p. 218) • CV power sources are designed to maintain selected arc voltage. They will maintain this preset voltage even with changes in electrode extension. An increase in electrode extension results in a slight increase in voltage. The increase in electrode extension also increases the resistance in the wire, which results in a decrease in the welding current because less current is required to maintain the same arc length. Similarly, a decrease in electrode extension decreases voltage slightly. The decrease in electrode extension reduces the resistance in the wire and results in an increase in current. (p. 219) • Electrode extension is the distance from the contact tip to the end of the welding wire. (p. 219) • A welding gun cable conducts the welding wire, shielding gas, and welding current to the welding gun. The welding gun cable contains a separate gas line for shielding gas, a current conductor to energize the electrode, and a gun cable liner that serves as a conduit for the welding wire. (p. 220) • The contact tip conducts current from the welding gun to the welding wire. Contact tips are available with different hole sizes. The diameter of the hole in the contact tip should match the diameter of the welding wire. (p. 221) • A worn, damaged, or oversized contact tip (contact tube) may cause problems with arc starting because of poor electrical contact. (p. 221) • The gas diffuser distributes shielding gas evenly around the welding wire and contact tip, and the gas nozzle directs the flow of shielding gas to the molten weld. (p. 221) • Spatter buildup on the gas nozzle, contact tip, and gas diffuser can restrict the flow of shielding gas. These components should be checked and cleaned regularly. (p. 221)  2015 by American Technical Publishers, Inc. All rights reserved

Instructional Plan Chapter 19 — GMAW – Equipment 81

• A dirty gun cable liner can cause problems with burnback and bird nesting. To keep the gun cable liner clean, blow shop air through it before installing a new spool of electrode wire. A damaged liner can also cause burnback or bird nesting. (p. 221) • A mixture of 75% Ar and 25% CO2 is commonly used for welding mild and low-alloy steels with short-circuiting transfer. A 75/25 mixture produces shallower penetration, faster travel speeds, a smoother and more focused arc, and less spatter than 100% CO2, making it ideal for autobody applications. (p. 228) • For most welding operations, the gas flow rate is approximately 20 cfh to 35 cfh. Insufficient shielding gas flow can cause porosity by allowing air to come into contact with the molten weld pool. (p. 228) • The copper coating on GMAW electrode wire aids in arc starting, improves wire feeding, and prolongs contact tip life. (p. 229) • The AWS classifies welding wire for GMAW using an alpha-numeric designation.

– The E stands for electrode.

– The R stands for rod and indicates that it can be used as a non-current-carrying filler rod, as in GTAW. – The number specifies the tensile strength of the deposited weld in thousands of pounds per square inch, for example, 70 = 70,000 psi.

– The S indicates a solid wire. The letter C is this position would indicate composite (metal Cored) wire.

– The digit following the dash indicates the chemical composition of the welding wire. (p. 229)

© 2015 American Technical Publishers, Inc. All rights reserved

82 Welding Skills Instructor Resources

 2015 by American Technical Publishers, Inc. All rights reserved