SAMPLE. MEM05019D Weld using gas tungsten arc welding process. Learner guide. MEM05 Metal and Engineering Training Package.

Transcription

1 MEM05 Metal and Engineering Training Package MEM05019D Weld using gas tungsten arc welding process Learner guide Version 1 Training and Education Support Industry Skills Unit Meadowbank Product code: 5613

2 Acknowledgments The 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 Davies Education Programs Manager TAFE NSW Enquiries Enquiries 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: Fax: 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 TAFE NSW (Training & Education Support Industry Skills Unit Meadowbank) 2012

3 Table of contents Introduction General introduction Using this learner guide Prior knowledge and experience Unit of competency overview Assessment Topic 1: Safety Hot metal, heat and arc rays Personal protective equipment (PPE) Review questions Topic 2: Basic electrical terms and definitions Review questions Topic 3: The gas tungsten arc welding process Industrial applications Advantages Limitations Power sources Polarity and current Torches and components Rating of power sources (Duty cycle) Review questions Topic 4: Welding consumables Tungsten electrodes Electrode preparation (dc current) Grinding techniques Shielding gases and gas mixtures Gas regulation Filler rods TAFE NSW (Training & Education Support Industry Skills Unit Meadowbank) 2012

4 Review questions Topic 5: Weld defects and faults Review questions Topic 6: Distortion control and weld joints Expansion and contraction Weld joints Purging Review questions Suggested practical jobs and projects Job 1 - Butt weld - flat Job 2 Butt weld - horizontal Job 3 Butt weld - vertical Job 4 Corner fillet - horizontal Job 5 Corner fillet - vertical Job 7 T-fillet - vertical Job 8 T-fillet weld - overhead Job 9 Lap fillet - horizontal/vertical Suggested project 1 Fillet and butt welds Resource Evaluation Form TAFE NSW (Training & Education Support Industry Skills Unit Meadowbank) 2012

5 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; or on Safe Work Australia; 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 hazards Working 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: Working on wet floors 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 If an exhaust fan is not available, an approved respirator should be used to filter out the dangerous fumes. TAFE NSW (Training & Education Support, Industry Skills Unit Meadowbank) 2012 Page 15 of 96

6 Dangerous fumes Gases, dusts and vapours are given off during welding. They can cause the following: Asphyxiation because the oxygen has been depleted from the work area (common in confined spaces) 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. Asphyxiation Welding in confined spaces (such as inside tanks, vessels and other enclosed containers) 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 danger in confined or poorly ventilated locations. Hot metal, heat and arc rays You 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 Page 16 of 96 TAFE NSW (Training & Education Support, Industry Skills Unit Meadowbank) 2012

7 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. Briefly explain the harmful effects the above arc rays can have on the welding operator. Page 18 of 96 TAFE NSW (Training & Education Support, Industry Skills Unit Meadowbank) 2012

8 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. Welding filter lens must be: o shade 13 minimum o approved and identified to Australian Standards 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 AS 1796 certification of welding operators and supervisors o NSW OHS act of 2000 o Metal and engineering award TAFE NSW (Training & Education Support, Industry Skills Unit Meadowbank) 2012 Page 19 of 96

9 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. Electricity Electricity is a form of energy associated with movement of electrons which create a magnetic field and heat energy. Voltage Voltage is the unit of electrical pressure. This electrical pressure (or force) is responsible for the current flow in a welding circuit. Voltage is commonly referred to as electro motive force (EMF). Current Current is the measure of the electron flow through a conductor. An ampere can be described as a measure (quantity) of electricity passing through a given point per second. This is similar to the rate water flows through a pipeline. Conductor In welding, an electrical conductor is a metal through which electricity will easily flow. Copper, brass and aluminium are widely used as conductors for welding equipment. Resistance Electrical resistance is a measure of how strongly a material opposes the flow of electric current. The unit of resistance is called ohms (Ω). The electric arc An arc is generated by electrons flowing across a gap between an electrode and a metal 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. The flow of electrons, that is the welding current, continues to flow across the small gap to establish an arc. Assisted by a shielding gas, the small gap becomes electrically charged or ionised and current is able to continue to flow across the gap in the form of an electric arc. power source ammeter welding lead welding torch A tungsten electrode A voltmeter work return workpiece Basic power circuit for GTAW TAFE NSW (Training & Education Support, Industry Skills Unit Meadowbank) 2012 Page 21 of 96

10 Review questions These questions have been included to help you revise what you have learnt in Topic 2: Basic electrical terms and definitions 1. Define the following electrical terms: Voltage: Current: 2. Label the parts indicated below associated with a basic GMAW power circuit. A 3. Briefly explain how an electric arc is generated when GTAW. A Multiple choice questions (Tick the box with the correct answer) 4. The unit of resistance in an electrical circuit is called: o ion o high frequency o ohm o electron 5. A material used as a conductor in MMAW electrode and return leads is: o carbon fibre 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 Page 22 of 96 TAFE NSW (Training & Education Support, Industry Skills Unit Meadowbank) 2012