MEM05018C Perform advanced welding using gas metal arc welding process (Aluminium edition) SAMPLE

Transcription

1 MEM05018C Perform advanced welding using gas metal arc welding process (Aluminium edition)

2 Publishing details: Published by Training and Education Support Industry Skills Unit, Meadowbank, - TAFE NSW in July 2009 Block J, Level 3, See Street Meadowbank NSW 2114 Copyright details: Training and Education Support Industry Skills Unit, Meadowbank, TAFE NSW, 2009 Copyright of this material is reserved to the Training and Education Support Industry Skills Unit, Meadowbank, TAFE NSW. Reproduction or transmittal in whole or part, other than for the purposes and subject to the provision of the Copyright Act, is prohibited without the written authority of Training and Education Support Industry Skills Unit, Meadowbank, TAFE NSW. Copyright acknowledgments: Training and Education Support Industry Skills Unit, Meadowbank would like to acknowledge the assistance and permission of the following companies for the use of copyright material. a2n management limited Bernard Welding BOC Australia Lincoln Electric (Australia) Cigweld Pty Ltd Murex Silverwater Welding Supplies Pty Ltd The Fabricator Welding Industries Australia (WIA) University of Ballarat ISBN Perform advanced welding using gas metal arc welding process MEM05018C/1 - Aluminium Edition FEEDBACK We value your opinion and welcome suggestions on how we could improve this resource manual. Keep in mind that the manual is intended to help students learn and is not a text book. Send your comments and suggestions to: Training and Education Support Industry Skills Unit, Meadowbank, TAFE NSW. Locked Bag 6 Meadowbank NSW 2114 Ph: (02) Fax: (02)

3 Contents Introduction...1 Advanced welding safety concepts...11 Review questions...15 Consumables used in Advanced GMAW...17 Review questions...27 Aluminium and aluminium alloys...31 Gas metal arc welding modes of metal transfer...43 Review questions...47 Weld joint pre-heating methods...51 Welding symbols...53 Destructive weld testing...59 Review questions...63 Welding aluminium structures...65 Review questions...67 Introduction to practical exercises and projects...69 Suggested practical exercises...71 Job 1 - Pad Weld...74 Job 2 - Horizontal / Vertical Fillet Weld...76 Job 3 - Horizontal / Vertical Corner Fillet Weld...78 Job 4 - Vertical Fillet Weld...80 Job 5 - Overhead Fillet Weld...82 Job 6 - Overhead Fillet Weld Pipe to Sheet...84 Job 7 - Flat Butt Weld...86 Job 8 - Horizontal Butt Weld...88 Job 9 - Vertical Butt Weld...90 MEM05018C-A/1 Perform advanced welding using GMAW process (Aluminium Edition) Industry Skills Unit, Meadowbank, TAFE NSW i

4 Advanced welding safety concepts This advanced unit of study in gas metal arc welding will require the student to have a greater degree of knowledge around safety issues relating to gas metal arc welding equipment, welding consumables and operating characteristics as well as being familiar with the every day risks and hazards of the process. Advanced welding operators, and welding personnel certified, or aiming for certification, against AS Certification of welders and welding supervisors, should be aware of modern advances in the process and safety issues. Such information is often available from Welding Industry periodicals, Welding Associations and welding related websites. Electric shock: low voltage Welding Operators are more likely to receive electric shocks on the secondary (low voltage) side of the welding circuit as opposed to the primary side of the electrical circuit, notwithstanding the usual risks associated with any piece of electrical equipment. The risk of electri is significantly reduced by: avoid working on wet floors - a shock may be flet when coming into contact with machine parts, torch or return lead clamps standing on insulated mats, or wooden boards Wearing dry leather gloves and PPE avoid working in a very humid climate or rainy weather - a shock may be felt when changing or installing an electrode. Keeping welding machine and equipment in good working order. Electric shocks: high voltage High voltage shocks can be avoided if: Welding machines are maintained by licensed electrical repairers Operators never interfere with the internal electrical components of welding machines. Symptoms of electrical shock The severity of an electric shock can range from a tingling sensation, muscle spasms, burns, or death. When electricity passes through the body, particularly through the arms or legs it causes muscles to contract. When the heart is in this current path it may stop your heart beating. Factors which affect the severity of the shock are: Open circuit voltage (OCV) of the welding machine Whether the welding power source supply is alternating (AC) or direct current (DC) Moisture from perspiration, humidity or other sources How well the operator is insulated from the electrode and the workpiece The parts of the body which are in contact with the work and/or the electrode current flow from hand to hand or hand to foot via the torso are the most dangerous. Electric currents near the heart or brain are particularly dangerous. Susceptibility of the victim to shock, which is dependent on general health and well being of the operator as well as other factors. MEM05018C-A/1 Perform advanced welding using GMAW process (Aluminium Edition) 11 Industry Skills Unit, Meadowbank, TAFE NSW

5 Advances in welding operator safety Safety investigations into workplace fatalities associated with electric arc welding have resulted in a tightening of the safety requirements associated with on-site arc welding. Changes are being implemented to on-site arc welding safety, to include among other things: All welding machines being of a DC welding circuit type; GMAW uses DC+ for all welding applications Inching control devices which enable wire electrodes to be fed from the wire feed unit through to the gun without the wire (momentarily) carrying welding current Welding machine power switched off or isolated on completion of welding; isolation switches could be mounted close to the welding operation or activated by an assistant when welding is completed Where existing machines do not have any of these characteristics/facilities, it is recommended that they be replaced or retrofitted to conform. Weld fumes Welding fumes consist of: particulate fume, the part you can see, and gaseous fume, the invisible part which you usually smell. Particulate fume is largely formed from vaporisation of the welding consumable. More than 90% of the fume arises from vaporisation of the consumable wire electrode as weld metal is transferred across the arc. The composition of particulate fume produced will depend on the composition of the wire electrode being used. To a lesser extent, particulate fume produced will also depend on the composition of the material being welded, such as chromium and nickel compounds within stainless steels. Gaseous fumes present when gas metal arc welding include ozone, oxides of nitrogen and carbon monoxide. The intense ultraviolet light emitted by the GMAW process acts on the oxygen in the surrounding atmosphere to form toxic ozone. Welding aluminium with an aluminium-silicon wire electrode in particular, produces high ozone exposure levels. High levels of nitrogen dioxide are produced in the arc. Because each of these gases is found in the fume column emitted by the gas metal arc welding process, adequate ventilation is required for the welders breathing zone. Due to the close proximity of the operator to the arc, the fumes generated in the gas metal arc welding process pose an immediate danger to the health & safety of the welding operator. The mode of metal transfer has a significant effect on fume levels produced by the GMAW process. When using spray arc metal transfer, the use of high current ranges and greater arc lengths generate higher levels of weld fumes compared to short arc gas metal arc welding. 12 MEM05018C-A/1 Perform advanced welding using GMAW process (Aluminium Edition) Industry Skills unit, Meadowbank, TAFE NSW

6 Summarising the causes and effects of gas metal arc welding fumes: Causes of fumes Elements within the wire electrode, such as chromium and nickel compounds found within stainless steel wire electrodes Elements within the parent metal The production of toxic gases such as ozone, nitrous gases and carbon dioxide/ monoxide. Over exposure to ozone may occur during gas metal arc welding of aluminium and stainless steels Ozone is formed during welding particularly when high currents are involved, by the action of ultraviolet radiation on oxygen in the air Surface coatings on metals being welded, such as degreasing solvents, lubricants and protective films used on aluminium and stainless steel Mode of metal transfer Weld fumes in the breathing area of the operators Effects of gases, dusts and vapours given off during welding Depending on the exposure time and volume of fume, breathing in these gases and vapours can cause: Respiratory ailments from irritation of the respiratory tract to serious lung disorders An acute flu-like illness called metal fume fever Asphyxiation because the oxygen has been used up in the work area (common in confined spaces) A build up of poisonous metals in the body from elements contained within the wire electrode such as zinc, magnesium, chronium and nickel etc. The study of fume exposure limits is carried out by OH&S (occupational health & safety) authorities and other governing bodies to measure the concentration of weld fumes in the breathing zone of the welding operator inside the head shield. On completion of the measurement period, a number is calculated that reflects an 8-hour time weighted average (TWA) of the fume concentration in the operator s breathing zone in milligrams of particulates per cubic metre of air. MEM05018C-A/1 Perform advanced welding using GMAW process (Aluminium Edition) 13 Industry Skills Unit, Meadowbank, TAFE NSW

7 Other terms used in the measurement and tabulation of fume concentration are: Threshold limit value (TLV) Permissible exposure limits (PEL) Short-term exposure limits (STEL) Analysis of the weld fume content, concentration and exposure levels are used by welding consumable manufacturers to produce safety information, known as Material Safety Data Sheets (MSDS). As well as providing details of the consumables, MSDS s also provide the welding operator with advice on exposure limits and suggested safety measures to limit inhalation of weld fumes. Respirator system worn by the welding operator Control measures for weld fumes In summary, the methods used to ensure the air is safe to breathe during welding are: Keep your head out of the fumes rising from the weld zone Use forced ventilation and respirators when welding dangerous fume producing metals such as aluminium, stainless steel, or coated metal surfaces including galvanised or cadmium coated steel. Also use a forced fume extraction system if welding is necessary in a confined area or where there is little air movement In a workshop that has a high roof, large doorways and windows, the natural movement of air will help dilute and remove welding fumes To filter out toxins, welding respirators must be worn if natural or forced ventilation is inadequate or the material being welded and/or the consumables are able to generate dangerous fumes Limit the exposure time to weld fumes (PEL & STEL), such as those times documented on welding consumable material safety data sheets (MSDS) Note: Respirators must be suitable for welding applications and manufactured in accordance with Australian Standard guidelines. 14 MEM05018C-A/1 Perform advanced welding using GMAW process (Aluminium Edition) Industry Skills unit, Meadowbank, TAFE NSW

8 Review Questions These questions will help you revise what you have learned from Advanced welding safety concepts. Q1. List two (2) possible causes of electric shock from the secondary (low voltage) side of the welding circuit: Q2. State four (4) factors which affect the severity of shock: Q3. Why does inching control protect the operator from electric shock when feeding electrode from the wire feed unit to the welding gun? Q4. List four (4) causes of weld fumes: Q5. In the space provided, briefly describe the possible effects of weld fumes on the welding operator: Q6. State four (4) precautions welding operators should take to ensure their air is safe to breathe during welding MEM05018C-A/1 Perform advanced welding using GMAW process (Aluminium Edition) 15 Industry Skills Unit, Meadowbank, TAFE NSW