wld 221 gas tungsten arc welding mild steel · 2018. 9. 22. · required text book and reading:...

WLD 221 Gas Tungsten Arc Welding

Mild Steel

NSF-ATE 2017Advanced Material Joining for Tomorrow’s Manufacturing Workforce

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INDEX

Syllabus 3-10

Information Sheets • GTAW Introduction• Uses of GTAW• Science on Steel• Math on Metal• Standard Power Source Controls• Torch Assembly• Tungsten Electrodes• Tungsten Preparation• Shielding Gases• Filler Metal Composition•

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13-1718-2425-3637-38

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Work Sheets • Power Source• Torch Assembly• Tungsten Electrodes• Shielding Gases

43-44454647

Welding Projects 48-82

Final Exam Information 83-84

Grading Rubric for the Practical Exam 85

Assessment Breakdown for the Course 86

This project was supported, in part, By the

National Science Foundation Opinions expressed are those of the authors And not necessarily those of the Foundation

PCC/ CCOG / WLD Course Number:

WLD 222

Course Title: Gas Tungsten Arc Welding: Aluminum

Credit Hours: 4

Lecture Hours: 0

Lecture/Lab Hours: 80

Lab Hours: 0

Special Fee: $24.00

Course Description Develops knowledge and skills required to weld common joints in all positions on aluminum

using the gas tungsten arc welding (GTAW) process. Prerequisites: Department permission

required. Audit available.

Addendum to Course Description This is an outcome based course utilizing a lecture/lab format. This course includes classroom discussions, videotapes, and lab demonstrations of technical skills. Course outcomes will include: theoretical concepts, layout, fabrication, welding and safety.

Intended Outcomes for the course Upon completion of the course students should be able to: • Function safely in the PCC Welding Lab. • Interpret blueprints to accurately lay out, prepare and assemble weld joints. • Understand and apply fundamentals of GTAW operations on aluminum. • Weld common joints assemblies with gas tungsten arc welding to AWS D1.1 Structural Steel

Welding Code visual acceptance criteria in all positions. • Apply visual examination principles and practices in accordance with AWS D1.1.

Course Activities and Design

Welding lec/lab courses are Open -Entry and Open Exit (OE/OE) and are offered concurrently. Courses are designed to meet the needs of the student with flexible scheduling options. Students may attend full time or part time. This is an OE/OE course which does not align with the normal academic calendar.

Outcome Assessment Strategies The student will be assessed on his/her ability to demonstrate the development of course outcomes. The methods of assessment may include one or more of the following: oral or written examinations, quizzes, written assignments, visual inspection,welding tests and task performance.

Course Content (Themes, Concepts, Issues and Skills) Function safely in the PCC Welding Shop. • Understand and practice personal safety by using proper protective gear • Understand and practice hand and power tool safety • Understand and maintain a safe work area • Recognize and report dangerous electrical and air/gas hose connections • Understand and practice fire prevention

Interpret drawing and symbols to accurately lay out, prepare and assemble weld joints on aluminum. • Interpret lines, symbols, views and notes • Lay out material per drawing specifications • Assemble project per specification

Understand and apply fundamentals of GTAW operations on aluminum. • Describe and demonstrate equipment setup, shut down and operation • Identify electrode types and preparation • Demonstrate proper arc length and travel speed • Demonstrate correct starting, stopping and restarting techniques • Demonstrate proper bead placement

Weld common joints with the Gas Tungsten Arc Welding (GTAW) to AWS code quality visual acceptance criteria in the following joints and positions. Demonstrate correct welding techniques on the following joints: Flat Position: • Fuse weld a flat position edge joint • Fuse weld a flat position corner joint

o Bead Plate o T-Joint o Butt Joint

Horizontal Position: • T-Joint • Lap Joint • Outside Corner Joint • Butt Joint

Vertical Position: • T-Joint • Lap Joint • Outside Corner Joint • Butt Joint

Over head Position:

• T-Joint • Lap Joint • Outside Corner Joint

Demonstrate visual examination principles and practices in accordance with AWS D1.1 Evaluate welds using appropriate welding inspection tools Assess weld discontinuities causes and corrections


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Course Assignments

Required text book and Reading: Welding Principles and Applications, By Larry Jeffus

Chapter 15, Gas Tungsten arc Welding Equipment, Setup, Operation and Filler Metals Chapter 16, Gas Tungsten Arc Welding of Plate

Information Sheets: Introduction to GTAW Filler Material Power Sources Set up procedures Welding Torch Craftsmanship expectations Tungsten Electrodes Visual inspection Shielding Gas

Video Training: “Gas Tungsten Arc Welding” by Miller GTAW 1,2,and 3 of the Miller Modular series Bergwall GTAW video series (4 videos)

Writing Work Sheets: Power Sources Welding Torch Tungsten Electrodes Shielding Gas

Welding Projects: Flat Position Horizontal Position Vertical Position Overhead Position Edge Joint T-Joint T-Joint T-JointCorner Joint Lap Joint Lap Joint Lap JointBead Plate Corner Joint Corner Joint Butt JointT-Joint Butt Joint Butt Joint

Final Exam: Part One (Closed Book Exam) Part Two (Practical Exam)


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Timeline: Open-entry, open-exit instructional format allows the students to work at their own pace. It is the student’s responsibility for completing all assignments in a timely manner. See your instructor for assistance.

Outcome Assessment Policy: The student will be assessed on his/her ability to demonstrate the development of course outcomes. The methods of assessment may include one or more of the following: oral or written examinations, quizzes, written assignments, visual inspection techniques, welding tests, safe work habits, task performance and work relations.

Grading criteria: The student's assessment will be based on the following criteria: 20% of grade is based on Safe work habits and shop practices. 20% of grade is based on Completion of written and reading assignments. 20% of grade is based on demonstrating professional work ethics (Habits). 40% of grade is based on completion of welding exercises.


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Grading scale: 90 - 100% A – Superior

Honor grade indicating excellence. Earned as a result of a combination of some or all of the following as outlined in the course training packet. Superior examination scores, consistently accurate and prompt completion of assignments, ability of to deal resourcefully with abstract ideas, superior mastery of pertinent skills, and excellence attendance. Probable success in a field relating to the subject or probable continued success in sequential courses.

80 - 89% B - Above average Honor grade indicating competence. Earned as a result of a combination of some or all of the following as outlined in the course training packet. High examination scores, accurate and prompt completion of assignments, ability to deal with abstract ideas, commendable mastery of pertinent skills and excellent attendance. Probable continued success in sequential courses.

70 - 79% C – Average Standard college grade indicating successful performance earned as a result of a combination of some or all of the following as outlined in the course training packet. Satisfactory examination scores, generally accurate and prompt completion of assignments, ability to deal with abstract ideas, fair mastery of pertinent skills and regular attendance. Sufficient evidence of ability to warrant entering sequential courses.

60 - 69% D – Substandard Substandard but receiving college credit. Substandard grade indicating that the student has met only minimum requirements as outlined in the c course training packet. Earned as a result of some or all of the following: low examination scores, generally inaccurate, incomplete or late assignments, inadequate grasp of abstract ideas, barely acceptable mastery of pertinent skills, irregular attendance, insufficient evidence of ability to make advisable the enrollment in sequential courses. Does not satisfy requirements for entry into course where prerequisite are specified.

0 - 59% F – Failure Non-passing grade indicating failure to meet minimum requirements as outlined in the course training packet. Earned as a result of some or all of the following: non-passing examination scores, inaccurate, incomplete or late assignments, failure to cope with abstract ideas, inadequate mastery of pertinent skills, repeated absences from class. Does not satisfy requirements for entry into course where prerequisites are specified.


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Pass Acceptable performance A grade of “P” represents satisfactory achievement that would have been graded “C” or better on the grading scale, but is given instead of a letter grade. By the end of the eighth (8th) week of class (or equivalent) students shall choose the graded or pass option. If they don’t choose the pass option, the class will be letter graded. By the end of the eighth (8th) week of class or equivalent), students may rescind an earlier request of the pass option.

No Pass No Pass Unacceptable performance or does not satisfy requirements for entry into courses where prerequisites are specified. This grade may be used in situations where an instructor considers the “F” grade to be inappropriate. The NP mark is disregarded in the computation of the grade point average.

CIPR Course In Progress Re-register A mark used to only for designated classes. To receive credit, a student must reregister because of equipment usage is required. This may include course in modular or self-paced programs. This mark may also be used in skill-based course to indicate that the student has not attained the skills required to advance to the next level. If the course is not completed within a year, the “CIPR” changes to an “AUD” (Audit) on the transcript unless the course was repeated and a grade earned.

AUD Audit Some courses may allow the students to attend a course without receiving a grade or credit for the course. Tuition must be paid, and instructor permission must be obtained during the first three weeks of class (or equivalent). Instructors are expected to state on their course handouts any specific audit requirements. Does not satisfy requirements for entry into courses where prerequisites are specified.

Repeated Courses Courses with grades of “D,” “F,” “NP,” or “CIP,” and “CIPR,” may be repeated for a higher grade. All grades earned will appear on the transcript. The first earned grade of “C” or “P” or better will count in the accumulated credit total. The first grade of “C” or better will be used for the GPA calculation.


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G.T.A.W. Introduction GTAW (Gas Tungsten Arc Welding), TIG (Tungsten Inert Gas), also sometimes referred to as “Heliarc.” Heliarc was a trade name of one of the first manufactures of the GTAW power sources. The GTAW process was developed in the period of 1940-1960 and rapidly became an indispensable welding method.

The complete name for the process is: Gas Refers to the substance that blankets the molten puddle and the arc.

Inert refers to a gas that will not combine chemically with other elements.

Tungsten Refers to the nonconsumable electrode that conducts electric current to the arc.

Arc Indicates that the welding is done by an electric arc rather than by the combustion of a gas.

Welding Coalescence is produced by heating with an arc between a tungsten electrode and the work. A filler material may or may not be added.

Advantages 1. GTAW will make high quality welds in almost all metals and alloys.2. No flux is required and finished welds do not have to be cleaned.3. The arc and weld pool are clearly visible to the welder.4. There is no filler metal carried across the arc so there is no spatter.5. Welding can be performed in all positions.6. There is no slag produced that might be trapped in the weld.7. There is a minimum distortion of the metal near the weld. The heat is

concentrated in a small area resulting is a small heat-affected zone.8. In the chemical composition, the weld is usually equal to the base metal. It

is usually stronger, more resistant to corrosion, and more ductile thanwelds made by other processes.

Disadvantages 1. More complex and expensive equipment is required.2. Higher operating cost (Argon gas and tungsten electrodes).3. Higher degree of manipulative skill is required.4. Extensive material preparation required. Welding area must be free of

contaminants such as oil, paint, rust, etc.5. Limited area of operations (nearly ideal conditions are required compared to

other welding processes).6. Slower deposit rates than other processes.


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Uses of GTAW The GTAW process is used when high quality and purity of the weld have priority over welding speed. GTAW is used in many welding manufacturing operations, primarily on thinner materials and where metal finishing is not desired. It is very useful for maintenance and repair work, for die-castings and unusual metals. GTAW is widely used for joining thin wall tubing and for making root passes on pipe joints.

The aircraft industry is one of the principle users of this process on such materials as aluminum, magnesium, titanium, and stainless steel. Products produced using GTAW include: space vehicles, rocket and jet engines, power industries, tanks, boilers and medical equipment.

GTAW Power Sources The welding power source used for GTAW is a constant current type of output. GTAW power sources may also be used for SMAW (Shielded Metal Arc Welding “stick”). There are a variety of types and models of GTAW power sources. Power source controls vary greatly from one manufacturer to another and from one model of machine to another. New technology is rapidly changing welding power sources, therefore it is necessary to study in greater detail the many adjustments available on the “state of the art” power sources in use today. We have utilized the owners manual information to review the controls on the different power sources. For the purpose of this course the focus will be on the power source controls that will be used during your Mild Steel training. Some more advanced features such as AC Wave Balance, and pulse features will be included in the Aluminum and Stainless Steel GTAW course work.

One of the many advances in welding power sources is the use of graphic symbols to identify controls. This provides communication on an international level. Please see the chart of graphic symbols following the power source information. An important outcome of your training is to develop knowledge and skills in the operation of a variety of GTAW power sources. This course will introduce the basic functions of the following GTAW power sources;

• Lincoln Idealarc 300• Lincoln Square Wave 255• Lincoln Square Wave 375• Lincoln Square Wave 355• Miller Syncrowave 350XL• Miller Syncrowave 250


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Science

on

Steel The Welding Fabrication Industry needs qualified welder fabricators who can deal with a variety of situations on the job. This portion of the training packet explores science as it relates to industry requirements.

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Contents of this Packet include - Weld Cleanliness- Electron Emission by Tungsten Electrode- Use of Thoriated and Ceriated Electrodes- Cleaning Action- Surface Tension Driven Flow of Weld Metal affecting Penetration

Weld CleanlinessCompared to SMAW, FCAW and GMAW, weld metal deposited by GTAW properly will be free of contamination of any kind. GTAW is a hydrogen-free process. The tungsten electrode and the molten metal pool are free of contamination because of the argon shielding gas used in welding. The only source of contamination is due to lack of good workmanship. Although GTAW is a very clean process, it can produce porous welds because of poor workmanship. For example, if the work-piece is covered with oil, grease or paint, the weld metal will contain porosity and be susceptible to hydrogen-assisted cracking.

Electron Emission by Tungsten Electrode The temperature of the central core of the arc in GTAW can approach approximately 30,000ºC (54,000º F). The presence of metal vapors from the filler metal and even the tungsten electrode itself will reduce the arc temperature slightly. The actual temperature of the arc during welding is limited by several sources of heat loss, namely;

- Radiation- Convection- Conduction and- Diffusion

Radiation from an arc varies from long wavelength infrared radiation to visible to short wavelength ultraviolet light. As intense as the gas tungsten arc is, the energy of the radiation is not high enough to produce x-rays, (which is abundantly generated in electron beam welding). The energy of radiation (Erad) is a function of the wavelength (w), as shown below:

Erad = h/w where h is Plank’s constant

The amount of arc radiation taking place during welding increases with arc temperature and atomic mass (of the media carrying the arc such as argon or helium). Using argon with GTAW, losses of up to 20% of the heat input are possible. Since the gas tungsten arc contains such intense ultraviolet energy, the problem to skin damage (similar to severe sunburns) takes place rapidly. Compared to GMAW, FCAW and SMAW, the GTAW process can cause the most severe skin burns if poor protective clothing is used.

Use of Thoriated and Ceriated Electrodes In DC operation, pure tungsten electrodes are not used because the tip of the electrode melts and the cathode spot moves unstably all over the molten ball. The erratic arc motion makes precision welding very difficult. The simple addition of 2%ThO2 (thoria) NSF-ATE 2017Advanced Material Joining for Tomorrow’s Manufacturing Workforce


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to the tungsten allows tungsten electrodes to operate at currents of 200 amps easily without the electrode melting. Furthermore, the 2% thoria electrodes nor only operate without melting, but also can achieve greater electron emission than pure tungsten. Thoria is a very stable compound and has a melting point (over 3,000ºC or 5,500ºF) almost as high as tungsten (3,410ºC). The mechanism by which this happens depends on the high-temperature solid state reaction between tungsten (W) and ThO2 to produce pure thorium (Th), as shown below:

W + ThO2 = WO2 + Th

At the very high temperatures experienced at the electrode tip during GTAW, the thorium diffuses to the outside surface of the electrode. During welding, the thorium-coated tungsten acts as if the electrode were entirely thorium. Thorium has a much lower work function than does tungsten. This means that the thorium-coated electrode can emit electrons with greater ease at lower temperatures than can tungsten. In fact, tungsten must be molten before it can achieve full thermionic emission of electrons. This is why AC welding of aluminum with pure tungsten electrodes requires that the tip of the tungsten be melted in the shape of a large ball. If pure tungsten does not have a melted ball at the electrode tip, the heat delivered by GTAW would be inadequate for welding because thermionic emission would not be achieved. The simple addition of 2%ThO2

permits thermionic emission without having to melt the electrode using either DC or AC. The current density achieved by 2%ThO2-W electrodes is about 10,000,000 A/m2.

Since ThO2 is mildly radioactive, research had been conducted over the years to find a substitute for ThO2. Ceria or CeO2, which is not radioactive, was found to be an excellent replacement of ThO2 as shown in Table 1, below.

Table 1 Tungsten electrode characteristic using argon shielding gas (Approximate values).

W W – 2%ThO2 W – 2%CeO2

Electrode Temperature, ºC Work function, eV Emissivity

3,450 3.0 0.15

3,300 2.4 0.22

2,800 2.1 0.30


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From Table 1, it can be seen that the electron work function is highest with pure tungsten and lowest with W-CeO2. The emissivity is lowest at the highest temperature for thermionic emission with pure tungsten; while, the emissivity of W- CeO2 is highest at the lowest temperature. This means that both W-ThO2 and W-CeO2 electrodes can operate below their melting points, while achieving full thermionic emission of electrons in the weld arc. These additions to tungsten have the beneficial effect of increasing arc stability.

In automatic welding at high current continuously for long periods of time may cause excess evaporation of the thorium. If the surface thorium content is too low, the electrode may become unstable by acting like a pure tungsten electrode. The development of ceriated electrodes and lanthanated electrodes provide extended arc stability for automatic welding. These additions of CeO2 and La2O3 diffuse much more slowly to the electrode surface because large tungstate and oxy-tungstate compounds form which are not very mobile at high temperatures. Thus, these ceriated and lanthanated electrodes have more long-term stability than thoriated electrodes.

Cleaning Action For all practical purposes, there is no cleaning action when GTAW of steel. Thus, steel is rarely ever welded with DCEP or AC. The action of the cathode removing oxides does take place when GTAW steel and can be observed. However, the cleaning action effect is minor and not considered of any value in welding steel. In welding of aluminum and magnesium, this cleaning action is extremely important and beneficial. The reason why the oxide layer on steel does not “clean” nearly as well as that for aluminum is related to the chemical stability, oxide thickness, relative melting points between oxide and substrate, and dielectric or electrical insulating properties. The melting points of steel and iron oxide are not nearly as different as those for aluminum and aluminum oxide. Similarly, the difference in chemical stability between aluminum oxide and pure aluminum is very great; while the difference between steel and iron oxide is not as large. Thus, when welding with DCEP and the work piece is the cathode (negative pole), the electrons tend to build up charge to a much greater extent with the aluminum cathode than with the steel cathode. Eventually, the charge build-up becomes so great in the case of welding aluminum that the aluminum oxide layer is virtually exploded away from the surface or “cleaned”. The same action takes place with steel except it is not strong enough to be beneficial. Thus, steel is almost always welded with DCEN.

Surface Tension Driven Flow of Weld Metal affecting Penetration Often when welding materials like 304 stainless steel by GTAW, the penetration will vary from heat to heat. Although the welding procedure is exactly the same, the width of the weld bead as well as the penetration will vary substantially depending on the residual elements in the steel. For example, the major alloying elements of 304 stainless are C, Cr, Ni, Mn and Si. Structural metals like steel and stainless steel contain many impurities in order to keep the cost of materials reasonable. Although the total amount of these impurities is small, these trace element impurities like S, P, O and others greatly affect the penetration and weld pool shape, because these elements are surface active agents. Although present in small quantities, these surface-active ingredients have a profound


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effect on the surface tension of the weld pool. For example, even water has surface tension, which is what allows small insects to walk on water as if it were solid. If a small amount of detergent were added to the water, the surface tension of the water would decrease dramatically causing wetting of the insects above it. Also, if the detergent is added to one side of the water and not the other, then surface tension driven flow can be observed. Similar, although more complex, reactions happen in weld metal deposited by GTAW especially if no filler metal is used, which is often the case in the nuclear industry.

Surface tension of the molten pool decreases with increasing temperature. The portion of the weld pool directly under the arc is hotter than the molten metal near the edges of the weld pool. Normally, the surface tension of the pool surface is greater at the edges than at the pool center; so, surface tension forces pulling from the edges of the molten pool drive flow. Liquid flow or convection is from the center of the pool toward the edges. This would produce relatively shallow but wide weld pools. Penetration in this case would be shallow. This is characteristic of GTAW of very pure metals.

If impurities like S, P, and/or O are present, surface tension at the weld edges are reduced so much by these surface active ingredients, that flow actually moves from the edge of the weld pool to the center of the pool. In this case, heat is driven by convection straight down from the arc into the weld pool causing substantially increased penetration and a narrow bead width. Often times, when welding to different pieces of stainless steel from different heats, a lop-sided weld bead develops. The reason is that one side (Side A) will not contain surface active agents, while the other (Side B) does contain surface active agents like S and O. Side A without surface-active agents will try to force the molten pool from under the arc to its edges. However, the other plate (Side B) will push molten metal from its edge to the center in the direction of Side A. As a result, the total flow is from Side B to Side A. By surface tension flow, the heat is being move from Side B to Side A. The weld bead shape will be lightly penetrated on Side B (with surface active agents) and highly penetrated on Side A without surface-active agents. This is because both sides cooperate to push metal from Side B to Side A.

Surface tension driven flow and weld penetration is also affected indirectly by the amount of deoxidizers in the steel. For example, if the stainless steel contains substantial aluminum killing agent, the aluminum will cleanse the weld of oxygen, which is a surface-active agent. So, if the oxygen were acting to cause deep penetration, the addition of aluminum deoxidizer would cause the weld pool to shallow and wide. Similarly, if calcium (Ca) is present as in Ca-treated steels, Ca immediately form CaS and removes sulfur from the molten pool. With sulfur present, the pool becomes deep; but, with sulfur removed by Ca, the molten pool is shallow and wide. So, if the welder notices differences in weld width and penetration (despite the fact than none of the welding conditions have changed), it is due to the different impurity level of the steel being welded.


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Math

on

Metal The Welding Fabrication Industry needs qualified welder fabricators who can deal with a variety of situations on the job. This portion of the training packet explores math as it relates to industry requirements.


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Lincoln Idealarc 300 Standard Power Source Controls

Current Selector Switch This allows you to select the welding current desired. The type of material to be welded determines the current choice. Direct current straight polarity (DCSP, DC-) is the current choice for mild steel.

Coarse Current Range Selector This adjustment allows you to select a wide current range usually labeled simply Low, Medium, and High with the minimum and maximum amperage available within each range listed below the range setting. Most of the newer machines have a single wide current range instead of low, medium and high, this allows adjustment of the full range of the current available

Fine Current Adjustment This adjustment allows you to select what percentage of the coarse range you wish to use. Usually a dial labeled 1 through 10. For example, if you have selected low range and your fine adjustment is set at 5, your available current will be 50% of the maximum current listed for low range.

Standard/Remote Contactor Control Switch When a remote contactor, such as a foot peddle for GTAW is being used, this switch must be in the "remote" position. The switch should be in the "standard" position when using the power source for SMAW.

Remote Amperage Control Receptacle This receptacle is provided for connecting a remote hand or remote foot control. This allows the operator to have amperage control while welding. When the foot control is completely depressed your welding current will be the maximum available as determined by coarse and fine current settings.

Post Flow This adjustment is an after timer for the flow of gas, sometimes labeled "post purge" or "after flow." This adjustment controls the length of time that the gas flows after the arc is broken. The flow of gas after the arc is broken protects the tungsten from atmospheric contamination as it cools, and protects the molten weld pool as it solidifies.

High Frequency Switch The high frequency current serves two purposes in GTAW. It provides a non-touch start in arc initiation and stabilizes the arc during AC welding applications. The switch has three positions, Continuous: Sometimes labeled "ON." In this position the high frequency is present all of the time during welding. When welding with AC it is necessary to have continuous high frequency to stabilize the alternating current.


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TORCH ASSEMBLY

The gas tungsten arc welding torch functions as an: electrode holder; a conduit for the shielding gas and coolant if used; and for a conductor of the welding current. Torches are available in a variety of sizes and shapes. Torches are rated by the maximum amperage they can carry. For example, air cooled torches are normally rated at about 150 amperes. This is the maximum welding current that can be safely used. Some water-cooled torches are rated at 500 amperes.


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The typical GTAW torch has several parts that include: 1. The cap seals the back of the torch and tightens to hold tungsten in place.

Caps are available in a variety of sizes. The one shown is for a seven inchlong tungsten.

2. "O" ring - fits on the cap to insure an air tight seal on the back of thetorch.

3. The tungsten is placed inside the torch. Tungstens are available in a widevariety of diameters and lengths.

4. Electrode collet:The collet holds the tungsten in place. The collet size must be the same asthe tungsten diameter. For example, if you are using a 1/16” diametertungsten you will need a 1/16” collet.

5. Torch body:Torch bodies are available in a variety of sizes and shapes. They arethreaded in the front and back for assembly.

6. Collet holder:The collet holder holds the collet in position and also disperses theshielding-gas into the gas cup. Some torches have universal colletholders. The torches in our shop do not. The collet and collet holder mustbe the same size as your tungsten diameter.

7. Gas nozzle:More commonly known as "gas cup," it directs the shielding gas over theweld pool. Cups are usually made of a high heat ceramic and are availablein many sizes. Cup size will vary with joint type for accessibility andtungsten diameter. Your cup should be 4 to 6 times larger than tungstendiameter. Cup sizes are measured in 1/16” of an inch. For example, anumber 4 cup would measure 4/16” inch (1/4”) in diameter and would besuitable for up to 1/16” diameter tungsten.


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Tungsten Electrodes Tungsten and tungsten alloys are the choice for electrode material because tungsten has the highest melting point of all metals (6,170° F) (3,410° C). Tungsten also offers low electrical resistance, good heat conductivity, and the ability to easily emit electrons. Four classes of tungsten electrodes have been standardized by the A.W.S. (American Welding Society). Shown below are A.W.S. classifications and color codes for the end of the electrodes. A.W.S. Classification* Type End Color E.W.P. Pure Tungsten green EWTH-1 1% Thorium added yellow EWTH-2 2% Thorium added red EWZr 50% Zirconium added brown Available diameters 0.020 to 0.250 inch (0.5 to 6.4 mm). Available lengths 3 to 24 inch (76 to 610 mm).

*AWS Classification System for Tungsten:EWTH-2 - E - electrode

W - atomic symbol for Tungsten (Wolfram)

Th2- alloy containing 2% Thorium

EWP - E - electrode, W – tungsten (Wolfram) P – pure

Pure tungsten is generally used for AC welding. The zirconium type is also excellent for AC. Thoriated tungsten electrodes are available for direct current straight polarity welding. The addition of thorium increases the current carrying capacity of the tungsten. Tungsten selection The material to be welded and the type of current used are the determining factors in the selection of type of tungsten. In welding of mild steel, use D.C.S.P.(Direct Current Straight Polarity) and a 2% thoriated tungsten (EWTh2). Selection of tungsten diameter will depend on the current range being used. The following chart recommends current ranges for tungsten diameters.

Typical current ranges for tungsten electrodes, DCSP, Argon shielding gas. Current Range (Amp.) Electrode Diameter (in.) 5 – 20 0.020 15 – 80 0.040 70 – 150 1/16 150 – 250 3/32 250 – 400 1/8 350 – 500 5/32 500 – 750 3/16 750 – 1000 ¼


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Tungsten Preparation

A sharpened point is used with direct current straight polarity (D.C.S.P). for carbon steels. Grinding should be done on a fine-grit hard abrasive wheel. To prevent contaminating the tungsten, this wheel should not be used to grind any other material. Use ONLY the grinder designated for tungsten only.

The tungsten should be ground vertically so the grind lines are in the same direction as current flow. This helps avoid spitting of tungsten particles into the weld. Light pressure only should be applied during grinding to avoid overheating of the tungsten. Blue spots are an indication of overheating.

ALWAYS WEAR EYE PROTECTION WHEN SHARPENING A TUNGSTEN!!! Tungsten electrodes are very brittle and easily shattered.

The condition of the tungsten tip is a very important factor in successful weld results. If the tip becomes contaminated during welding, it must be re-sharpened.


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Shielding Gases

The type of shielding gas used in GTAW is inert. Inert means that the gas does not form compounds with other elements and is nonflammable. Argon and helium are two inert shielding gases used in GTAW.

Argon is most commonly used. It is readily available, heavier than helium and slightly heavier than air. This provides a more efficient arc shielding at lower flow rates. Argon is also better for arc starting and operates at lower arc voltage.

Helium provides higher arc voltage resulting in deeper penetration than argon. It is also possible to weld at higher speeds with helium. Helium is lighter than Argon or air and tends to float away from the weld zone so higher flow rates are required. In some cases argon and helium are mixed together for a particular welding application.

Shielding gas may be supplied from cylinders or a manifold system. A combination regulator and flow meter is usually used. The regulator reduces the high pressure of the cylinder to a usable working pressure. The flow meter provides uniform flow of shielding. It is calibrated to show flow in cubic feet per hour (c.f.h.). Flow should be adjusted by turning the adjusting knob; reference the flow meter to determine whether reading the top, middle, or bottom of the ball when setting the flow. Because of the difference in gas densities, flow meters must be designed for the specific gas being used.

Flow meter adjusting knob

Cylinder Pressure Gage

Cylinder on/off valve

Safety valve for the cylinder

Cylinder with flow meter

For your practice, in our shop, 15 to 20 cubic feet per hour (c.f.h.) of argon is usually a good working range. Some factors that may affect the flow rate are listed below:

1. Type of shielding gas 4. Size of cup2. Type and design of weld joint 5. Size of puddle3. Cup to work distance 6. Position of welding

7. Air drafts in the welding area


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Filler Metal Composition

As in all welding, the filler material must be similar in composition but not necessarily identical to the metal being welded.

Mild steel identifies those steels whose carbon content is in the range of 0.03% to .30%. These are also known as low carbon steels or plain steels. Mild steel is produced in greater quantities than all other steels combined. The weldability and machinability of mild steel is excellent. It is the most widely used and can be found in structures fabricated by welding such as bridges, ships, tanks, pipes, buildings, railroad cars, automobiles, and many more. Besides carbon, steel is made up of iron, silicon, sulfur, phosphorus, and manganese. Carbon is the most important alloying element in steel. An increase of as little as 0.1 percent carbon can change all of the properties of steel.

Selection of filler size will vary with joint requirements and current range. A good working rule is to select the same diameter filler as the tungsten you are using.

Note: see AWS Standards A5.18 and A5.28 for a description of each classification of filler material.

Filler metal identification

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Power Source Worksheet

Name: _____________________________ Date: ____________________ Directions: Define the following terms. Use Welding Principles and Applications, WLD 221, Training Packet Information Sheets, or the text books in the Welding Resource Room (Bldg 2/132a) to answer these questions.

1. What type of output is needed in a power source used for GTAW?

2. What other welding process uses this type of power source?

3. What determines the type of current to be used in GTAW?

4. List two things to be considered when adjusting the amount of amperage to be used.

5. Which two controls on the power source are used when adjusting amperage?

6. Define post flow, and explain its purpose.



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7. List the two functions of the high frequency current in GTAW

8. When welding mild steel, which current is used?

9. When welding Aluminum, which current is used?

10. Give an advantage of remote controlled amperage

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Torch Assembly Worksheet


1. How are T.I.G. torches rated?

2. How do you know what size collet you need?

3.What are the two functions of a collet holder?

4. List two methods of cooling a T.I.G. torch.

5.What factors are considered when selecting a gas cup?



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Tungsten Electrodes Worksheet


1. Why are tungsten and tungsten alloys the choice of electrodes in GTAW?

2. How do you know what size tungsten to use?

3. Why is thorium alloyed with tungsten?

4. How is tungsten prepared for mild steel welding applications?

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Shielding Gas Worksheet


1. What type of gas is used for shielding in GTAW?

2. Why is argon more common than helium as a shield?

3. What is one advantage of helium as a shield?

4. How are shielding gases supplied?

5. Define c.f.h. and explain what it measures in GTAW.



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Craftsmanship Expectations for Welding Projects

Steps in completing welding projects: 1. Thoroughly read each drawing.2. Utilize scrap material to adjust machine.3. Assemble the welding projects per drawing specifications.4. Review the Welding Procedure portion of the prints to review welding

parameter information.5. Complete welding project. Practice as needed to meet acceptance criteria

listed below.6. Complete the student assessment piece on the project sheet and submit.7. Submit project to the instructor for the final grading.

Factors for grading welding projects are based on the following criteria

Metal Preparation Project Layout Weld Quality Thoroughly clean metal Correct joint assembly See chart below

(+/- 1/16”)

Weld Quality per AWS D1.1 VT Criteria Cover Pass Weld Size See specification on drawing Undercut 1/32” deep

Weld Contour Smooth Transition Penetration N/A

Cracks None Allowed Arc Strikes None Allowed

Fusion Complete Fusion Required Porosity None Allowed Overlap None Allowed

Example of a High Quality Weld


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Set Up Procedure Material preparation Cleanliness of material is a critical factor of success in GTAW. All surface contamination must be removed. Use an emery cloth for removing of mill scale on the sheared sheet material. You will need

• EWth2 - (size selected according to material thickness and current range,available in sizes 1/16”, 3/32”, and 1/8”).

• Collet - same size as tungsten.• Collet holder - same size as tungsten.• Ceramic cup - size will vary with joint type and tungsten diameter.

Tungsten Preparation • Grind to a point using the grinder designated for tungsten only in GTAW area. Do

not grind the end with the red band on it.Torch Assembly

• Loosen cap of torch until "0" ring is visible.• Insert tungsten in collet and collet into collet holder. Screw this assembly into

front of torch, finger tight only.• Screw on ceramic cup and adjust tungsten stick out (the distance the tungsten

extends beyond the cup). Tungsten stick out will vary with joint type. Stick outshould be long enough to insure proper arc length but should not exceed your cupdiameter to insure proper shielding

• Tighten torch cap to secure tungsten position finger tight only.

Machine Adjustment • Polarity switch should be set on direct current straight polarity (D.C.S.P.).• Current range is adjusted by setting coarse adjustment and fine adjustment

according to electrode diameter, material thickness and weld joint requirement.• Remote/Standard switch - set on remote.• Post flow timer adjusted to sufficiently shield tungsten and weld crater.• High frequency switch should be in start position.• High frequency adjustment - should be sufficient enough to start the arc. This

will vary with tungsten size and joint type.• Turn power switch on.• Depress foot control to initiate gas flow and water (if water cooled torch).• Make sure torch is not in contact with grounded surface or it will arc. Set gas flow

rate at 10 - 15 c.f.h. by adjusting knob on flow meter. Check water return line tosee that water is flowing.

• Test machine adjustments on a piece of scrap.


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GTAW Flat Position Edge Joint (Fuse Weld) Project #1 Objectives of this welding exercise are: • To learn how to set up and adjust the equipment.• To develop your ability to control travel speed and arc length.• Your goal is to fuse the edge surfaces resulting in a smooth rounded contour on all

sides of the joint. Note that when “fuse” welding no filler material is added.Cause and effect factors Amperage

Too high = undercutting Too low = lack of fusion on the edges of the joint

Travel Speed Too slow = excessive heat, irregular shape, burning away of the edge Too fast = weld does not wrap the edges of the plates leaving them sharp and jagged.

Arc length Too short = touching the tungsten to the work, contaminating the tungsten and the work. Too long = undercutting, and can result in loss of gas coverage creating porosity.

VT Criteria Student Assessment Instructor Assessment Weld Size Undercut

Weld Contour Penetration

Cracks Arc Strikes

Fusion Porosity Overlap

Completed GRADE


50


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GTAW Flat Position Corner Joint (Fuse Weld) Project #2 Objectives of this welding exercise are: • To practice set up and adjustment of the equipment.• To develop consistency in control of travel speed and arc length.• Your goal is to fuse the edge surfaces resulting in a smooth rounded contour on all

sides of the joint. Note that when “fuse” welding no filler material is added.Cause and effect factors Amperage

Too high = undercutting, or melting holes through the work Too low = lack of fusion on the edges of the joint

Travel Speed Too slow = excessive heat, irregular shape, burning holes Too fast = weld does not wrap the edges of the plates leaving them sharp and jagged.

Arc length Too short = touching the tungsten to the work, contaminating the tungsten and the work. Too long = undercutting, and can result in loss of gas coverage creating porosity.



Cracks Arc Strikes


Completed GRADE


52


53

GTAW Flat Position Butt Joint Project #4 Objectives of this welding exercise are: • To practice set up and adjust of the equipment for a different application.• To develop consistency in your ability to control travel speed and arc length.• To develop the ability to add filler material to the weld pool.



Cracks Arc Strikes


Completed GRADE


54


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GTAW Flat T Joint Project #5 Objectives of this welding exercise are: • To practice set up and adjust of the equipment for a different application.• To develop consistency in your ability to control travel speed and arc length.• To develop the ability to add filler material to the weld pool.



Cracks Arc Strikes


Completed GRADE


56


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GTAW Horizontal T Joint Project #6 Objectives of this welding exercise are: • To practice set up and adjust of the equipment for a different application.• To develop consistency in your ability to control travel speed and arc length.• To develop the ability to add filler material to the weld pool.



Cracks Arc Strikes


Completed GRADE


58


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GTAW Horizontal Lap Joint Project #7 Objectives of this welding exercise are: • To practice set up and adjust of the equipment for a different application.• To develop consistency in your ability to control travel speed and arc length.• To develop the ability to add filler material to the weld pool.



Cracks Arc Strikes


Completed GRADE


60


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GTAW Horizontal Corner Joint Project #8 Objectives of this welding exercise are: • To practice set up and adjust of the equipment for a different application.• To develop consistency in your ability to control travel speed and arc length.• To develop the ability to add filler material to the weld pool.



Cracks Arc Strikes


Completed GRADE


62


63

GTAW Horizontal Butt Joint Project #9 Objectives of this welding exercise are: • To practice set up and adjust of the equipment for a different application.• To develop consistency in your ability to control travel speed and arc length.• To develop the ability to add filler material to the weld pool.



Cracks Arc Strikes


Completed GRADE


64


65

GTAW Vertical T Joint Project #10 Objectives of this welding exercise are: • To practice set up and adjust of the equipment for a different application.• To develop consistency in your ability to control travel speed and arc length.• To develop the ability to add filler material to the weld pool.



Cracks Arc Strikes


Completed GRADE


66


67

GTAW Vertical Lap Joint Project #11 Objectives of this welding exercise are: • To practice set up and adjust of the equipment for a different application.• To develop consistency in your ability to control travel speed and arc length.• To develop the ability to add filler material to the weld pool.



Cracks Arc Strikes


Completed GRADE


68


69

GTAW Vertical Position Corner Joint Project #12 Objectives of this welding exercise are: • To practice set up and adjust of the equipment for a different application.• To develop consistency in your ability to control travel speed and arc length.• To develop the ability to add filler material to the weld pool.

.



Cracks Arc Strikes


Completed GRADE


70


71

GTAW Vertical Position Butt Joint Project #13 Objectives of this welding exercise are: • To practice set up and adjust of the equipment for a different application.• To develop consistency in your ability to control travel speed and arc length.• To develop the ability to add filler material to the weld pool.



Cracks Arc Strikes


Completed GRADE


72


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GTAW Overhead Position T Joint Project #14 Objectives of this welding exercise are: • To practice set up and adjust of the equipment for a different application.• To develop consistency in your ability to control travel speed and arc length.• To develop the ability to add filler material to the weld pool.



Cracks Arc Strikes


Completed GRADE


74


75

GTAW Overhead Position Lap Joint Project #15 Objectives of this welding exercise are: • To practice set up and adjust of the equipment for a different application.• To develop consistency in your ability to control travel speed and arc length.• To develop the ability to add filler material to the weld pool.



Cracks Arc Strikes


Completed Grade


76


77

GTAW Overhead Position Butt Joint Project #16 Objectives of this welding exercise are: • To practice set up and adjust of the equipment for a different application.• To develop consistency in your ability to control travel speed and arc length.• To develop the ability to add filler material to the weld pool.



Cracks Arc Strikes


Completed GRADE


78


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Final Exam

Part One This portion of the final exam is a closed book test. Consult with your instructor to determine items that you may need to review. Once you determine that you are ready for the exam proceed to the Student Learning Center (Bldg 2 Rm. 212) and request the exam at the front counter. Complete the exam and write all answers on the answer sheet. Once completed, return the exam and answer sheet to the front desk.

Part Two This portion of the exam is a practical test where you will fabricate and weld a weldment from a “blue print”. The evaluation of this portion of the exam will be based on the rubric. You will have two class periods to build the project.


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Final Grading Rubric for practical exam

Class Name: WLD 221 Name:________________________________ Date:_______________________Hold Points are mandatory points in the fabrication process, which require the inspector to check your work. You are required to follow the hold points. PointsPossible

HoldPoints Instructor’s Evaluation

5points BlueprintInterpretationandMaterialCutList

5 points = 0 errors, all parts labeled and sized correctly 3points=1errorinpartsizingand/oridentification2points=2errors1point=3errors0points=4ormoreerrors

10points MaterialLayoutandCutting(Tolerances+/-1/16”)10points Layoutandcuttingto+/-1/16” Smoothnessofcutedgeto1/32”7pointsLayoutandcuttingto+/-1/8”Smoothnessofcutedgeto1/16REWORKREQUIREDIFOUTOFTOLERANCEBYMORETHAN1/8INCH

10points Fit-upandTackweld(Tolerances+/-1/16”)10pointsTolerances+/-1/16” Straightandsquareto+/-1/16”7Points Tolerances+/-1/8” Straightandsquareto+/-1/8”REWORKREQUIREDIFOUTOFTOLERANCEBYMORETHAN1/8INCH

15points WeldQualitySubtract1pointforeachwelddiscontinuity,incorrectweldsizeandincorrectspacingsequence.

28points Minimumpointsacceptable.ThisequatestotheminimumAWSD1.1Coderequirements.

TotalPoints /40

WLD221GTAWMildSteel:ProjectAssessmentFormStudentName:________________Date_________FlatPosition Assessment InstructorSignature/DateEdgeJoint–FuseWeld CornerJoint–FuseWeld ButtJoint T-Joint HorizontalPosition Assessment InstructorSignature/DateT-Joint LapJoint CornerJoint ButtJoint VerticalPosition Assessment InstructorSignature/DateT-Joint LapJoint CornerJoint ButtJoint OverheadPosition Assessment InstructorSignature/DateT-Joint LapJoint ButtJoint

wld 221 gas tungsten arc welding mild steel · 2018. 9. 22. · required text book and reading:...

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