mem05019d weld using gas tungsten arc welding process · multiple choice questions (tick the box...

MEM05 Metal and Engineering

Training Package

Learner guide

Version 1

Training and Education Support

Industry Skills Unit

Meadowbank

Product code: 5613

MEM05019D Weld using gas tungsten

arc welding process

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© TAFE NSW (Training & Education Support Industry Skills Unit Meadowbank)

2012

MEM05019D Weld using gas tungsten arc welding process

AcknowledgmentsThe TAFE NSW Training and Education Support Industry Skills Unit, Meadowbank would like to acknowledge the support and assistance of the following organisations and people in the production of this learner guide:

• BOC Gases• CIGWELD Australia• ESAB• Fronius/Smenco Australia• Lincoln Electric Co (Australia) Pty Ltd• Standards Australia• The Fabricator• Welding Industries of Australia (WIA)

Writer:Jim Miles (from existing TAFE Resources)

Reviewer:Vince Aranda (Illawarra Institute)

Project Manager:Stephen DaviesEducation Programs ManagerTAFE NSW

EnquiriesEnquiries about this and other publications can be made to:

Training and Education Support Industry Skills Unit, Meadowbank Meadowbank TAFE Level 3, Building J, See Street, MEADOWBANK NSW 2114

Tel: 02-9942 3200 Fax: 02-9942 3257

© TAFE NSW (Training and Education Support, Industry Skills Unit Meadowbank) 2012

Copyright of this material is reserved to TAFE NSW Training and Education Support, Industry Skills Unit Meadowbank. Reproduction or transmittal in whole or in part, other than subject to the provisions of the Copyright Act, is prohibited without the written authority of TAFE NSW Training and Education Support, Industry Skills Unit Meadowbank.

ISBN 978 1 74236 327 1

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2012


Table of contents

Introduction ................................................................................... 5

1. General introduction ............................................................................. 5

2. Using this learner guide ......................................................................... 5

3. Prior knowledge and experience ............................................................. 6

4. Unit of competency overview ................................................................. 7

5. Assessment ....................................................................................... 10

Topic 1: Safety ............................................................................. 15

Hot metal, heat and arc rays ................................................................... 16

Personal protective equipment (PPE) ......................................................... 16

Review questions ................................................................................... 18

Topic 2: Basic electrical terms and definitions .............................. 21


Topic 3: The gas tungsten arc welding process ............................ 23

Industrial applications ............................................................................. 24

Advantages ........................................................................................... 24

Limitations ............................................................................................ 24

Power sources ....................................................................................... 25

Polarity and current ................................................................................ 28

Torches and components ......................................................................... 30

Rating of power sources (Duty cycle) ........................................................ 34


Topic 4: Welding consumables ..................................................... 41

Tungsten electrodes ................................................................................ 41

Electrode preparation (dc current) ............................................................ 42

Grinding techniques ................................................................................ 43

Shielding gases and gas mixtures ............................................................. 44

Gas regulation ....................................................................................... 46

Filler rods .............................................................................................. 49

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Topic 5: Weld defects and faults .................................................. 55


Topic 6: Distortion control and weld joints ................................... 61

Expansion and contraction ....................................................................... 61

Weld joints ............................................................................................ 62

Purging ................................................................................................. 63


Suggested practical jobs and projects .......................................... 67

Job1-Buttweld-flat ............................................................................ 70

Job 2 – Butt weld - horizontal .................................................................. 72

Job 3 – Butt weld - vertical ...................................................................... 74

Job4–Cornerfillet-horizontal ............................................................... 76

Job5–Cornerfillet-vertical ................................................................... 78

Job7–T-fillet-vertical .......................................................................... 82

Job8–T-filletweld-overhead ................................................................ 84

Job9–Lapfillet-horizontal/vertical ........................................................ 86

Suggested project 1 – Fillet and butt welds ................................................ 88

Resource Evaluation Form ............................................................ 93

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© TAFE NSW (Training & Education Support, Industry Skills Unit Meadowbank) 2012 Page 15 of 96

Topic 1: Safety

The Work, Health and Safety Act 2011 (WHS Act) and WHS Regulations are enforced throughout all Australian States and Territories. This legislation is aimed at providing consistency, certainty and clarity across Australia making it easy to understand workplace health and safety responsibilities. Consequently this act and its regulations requires employers, employees, contractors and visitors on a worksite to take every reasonable step to work safely and responsibly in the workplace.

There are no "short cuts" to working safely, its everyone's responsibility to either eliminate and minimise potential risks in the workplace, report faulty equipment, unsafe environments and comply with WHS policies and procedures. Detailed information relating to the WHS Act and regulations can be found on:

• WorkCover Authority of NSW website; www.workcover.nsw.gov.au or on

• Safe Work Australia; www.safeworkaustralia.gov.au

WORK

SAFE HOME

SAFE

Welding operators must know about the principles governing the welding operation, equipment used and workplace health and safety precautions required. The following points need to be taken into account when working in a welding environment.

Welding hazardsWorking with electrical equipment can be hazardous. You must take proper precautions and follow the set safety procedures.

Electric shocks (low voltage)Electric shocks are possible on the secondary (low voltage) side of the welding circuit. They may be caused by:

• Workingonwetfloors

• Working in a very humid conditions or wet weather

Always stand on insulated mats or wooden boards and wear dry leather gloves to reduce the risk of electric shock.

Electric shock can be severe with all welding processes but with GTAW it is effectively increased by the use of high frequency (HF) for a non-touch start.

Welding fumes• Welding must always be carried out in well ventilated areas

• Ifanexhaustfanisnotavailable,anapprovedrespiratorshouldbeusedtofilterout the dangerous fumes.

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© TAFE NSW (Training & Education Support, Industry Skills Unit Meadowbank) 2012Page 16 of 96

Dangerous fumesGases, dusts and vapours are given off during welding. They can cause the following:

• Asphyxiation because the oxygen has been depleted from the work area (commoninconfinedspaces)

• A build up of poisonous metals in the body, such as lead, cadmium, zinc, beryllium or mercury

• Can cause respiratory ailments from wheeziness to serious lung disorders

• Intense GTAW ultra-violet rays close to the arc can result in the surrounding oxygen being transformed into poisonous ozone.

Sources of fumes• The production of oxides and nitrous gases

• Incomplete combustion or oxidation of nitrogen from the atmosphere

• Elements within the metal being welded

- Alloying elements of stainless steel such as chromium and nickel - Iron/manganese fume - Metal fume.

AsphyxiationWelding in confined spaces (such as inside tanks, vessels and other enclosedcontainers) produces concentrated levels of ozone, nitrous oxide and other gases which can cause asphyxiation. These areas must be properly ventilated to avoid oxygen displacement and depletion.

High frequency has a tendency to cause a corona discharge which breaks down the rubber insulation of the power cable producing noxious fumes which is an added dangerinconfinedorpoorlyventilatedlocations.

Hot metal, heat and arc raysYou can avoid the effects of these hazards by wearing proper protective clothing, footwear, and appropriate equipment.

Personal protective equipment (PPE)• Welding helmet• Leather gloves or GTAW pig skin gloves• Safety boots or shoes with steel caps• Safety glasses• Overalls• Ear plugs

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Review questions

These questions have been included to help you revise what you have learnt in Topic 1: Welding safety.

1. List three (3) precautions welding operators must take to avoid an electric shock. ______________________________________________________________ ______________________________________________________________ ______________________________________________________________

2. List five (5) items of protective clothing and equipment (PPE) GTAW operators are expected to wear. ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________

3. Other than electric shock, list two (2) hazards associated with working in a welding environment. ______________________________________________________________ ______________________________________________________________

4. Name the two (2) harmful rays emitted from a GTA welding arc. ______________________________________________________________ ______________________________________________________________

5. Brieflyexplaintheharmfuleffectstheabovearcrayscanhaveontheweldingoperator. ______________________________________________________________ ______________________________________________________________

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Multiple choice questions (Tick the box with the correct answer)

6. Welding over galvanized steel will produce:

o rust resistant welds o stronger welds o poisonous fumes o more ductile welds

7. Weldingfilterlensmustbe:

o shade 13 minimum o approvedandidentifiedtoAustralianStandards o made in Australia o green

8. Ensuring a safe working environment is the responsibility of the:

o employer and employee o welding supervisor o owner of the business o chief engineer

9. The legislation governing the safety of Australians in the workplace is the:

o Work Health and Safety act of 2011 o AS1796certificationofweldingoperatorsandsupervisors o NSW OHS act of 2000 o Metal and engineering award

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Topic 2: Basic electrical terms and definitions The heat energy required for gas tungsten arc welding is generated by an electric arc between a non-consumable tungsten electrode and the workpiece. The application of electricity means it is important that welding operators have a basic understanding of electrical terminology and principles associated with the GTAW process.

ElectricityElectricity is a form of energy associated with movement of electrons which create a magneticfieldandheatenergy.

VoltageVoltage is the unit of electrical pressure. This electrical pressure (or force) is responsibleforthecurrentflowinaweldingcircuit.Voltageiscommonlyreferredtoas electro motive force (EMF).

CurrentCurrentisthemeasureoftheelectronflowthroughaconductor.Anamperecanbedescribed as a measure (quantity) of electricity passing through a given point per second.Thisissimilartotheratewaterflowsthroughapipeline.

ConductorIn welding, an electrical conductor is a metal through which electricity will easily flow.Copper,brassandaluminiumarewidelyusedasconductorsforweldingequipment.

ResistanceElectricalresistanceisameasureofhowstronglyamaterialopposestheflowofelectric current. The unit of resistance is called ohms (Ω).

The electric arcAnarcisgeneratedbyelectronsflowingacrossagapbetweenanelectrodeandametal workpiece, the electrical energy being changed into heat and light. In the case of GTAW, the arc is initiated by means of a spark generated by high frequency (HF) voltage, across the air gap between the electrode and the workpiece.

Theflowofelectrons,thatistheweldingcurrent,continuestoflowacrossthesmallgaptoestablish an arc. Assisted by a shielding gas, the small gap becomes electrically charged or ionisedandcurrentisabletocontinuetoflowacrossthegapintheformofanelectricarc.

A

A

power sourceammeter

voltmeter

welding leadwelding torch

tungsten electrode

workpiece

workreturn

Basic power circuit for GTAW

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Review questionsThese questions have been included to help you revise what you have learnt in Topic 2: Basic electrical terms and definitions

1. Definethefollowingelectricalterms:

Voltage: _______________________________________________________

Current: _______________________________________________________

2. Label the parts indicated below associated with a basic GMAW power circuit.

A

A

3. BrieflyexplainhowanelectricarcisgeneratedwhenGTAW.

______________________________________________________________ ______________________________________________________________ ______________________________________________________________

Multiple choice questions (Tick the box with the correct answer)

4. The unit of resistance in an electrical circuit is called:

o iono high frequency o ohmo electron

5. A material used as a conductor in MMAW electrode and return leads is:

o carbonfibre o carbon steel o copper o reinforced rubber

6. Electricity is a form of energy associated with:

o gravitational forces o arc radiation o expansion of resistors o movement of electrons

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mem05019d weld using gas tungsten arc welding process · multiple choice questions (tick the box...

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