SAMPLE. Weld using flux cored arc welding process (MEM05047B) LEARNING RESOURCE MANUAL. Metal Fabrication & Welding T INDUSTRY SKILLS UNIT MEADOWBANK

Transcription

1 Weld using flux cored arc welding process (MEM05047B) LEARNING RESOURCE MANUAL T INDUSTRY SKILLS UNIT MEADOWBANK Metal Fabrication & Welding MEM05047B/1 First Edition Product Code: 2966

2 Publishing details: Published by Manufacturing, Engineering, Construction and Transport Curriculum Centre - TAFE NSW in March 2008 Corner Showground and Green Roads, Castle Hill, NSW 2154 Copyright details: Manufacturing, Engineering, Construction and Transport Curriculum Centre, TAFE NSW, 2008 Copyright of this material is reserved to the Manufacturing, Engineering, Construction and Transport Curriculum Centre, 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 Manufacturing, Engineering, Construction and Transport Curriculum Centre, TAFE NSW. Copyright acknowledgments: MEC&T Curriculum Centre would like to acknowledge the assistance and permission of the following companies for the use of copyright material: Cigweld Pty Ltd Lincoln Electric (Aust) Pty Ltd ESAB Welding Industries Australia (WIA) Weld using f ux cored arc welding process MEM05047B 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 Level 3, Building J, See Street MEADOWBANK NSW 2114 Ph: (02) Fax: (02)

3 Contents Introduction Scope of Unit and Performance Criteria...1 Student Assessment Guide...3 Unit Purpose...3 Prerequisites...3 Assessment...5 Unit Mapping...5 Recognition of Prior Learning (RPL)...5 Theory Flux cored arc welding (FCAW) operating principles...8 Applications...14 FCAW accessories...17 Maintenance of welding accessories...18 Electrode Classif cation...18 Self-shielding wires...20 Electrical stick-out distance...21 Typical operational data for types of FCAW wire electrodes...22 Care and Storage of Flux Cored Wire electrodes...24 Shielding gases...25 Advantages of FCAW...30 Machine faults associated with FCAW...31 Safety hazards...34 Distortion...36 Joints...37 Review questions...41 Practical exercises and projects Horizontal / vertical f llet welds...48 Horizontal / vertical f llet welds on plate to section...50 Vertical f llet welds...52 Overhead f llet welds...54 Corner f llet welds...56 Single bevelled butt welds...58 Flat butt welds with backing strip...60 Horizontal double vee butt welds...62 Vertical double vee butt welds...64 Suggested practical welding assessment...66 MEM05047B Weld using flux cored arc welding process i

4 Theory MEM05047B Weld using flux cored arc welding process 7

5 Flux cored arc welding operating principles Objectives: At the end of this unit you will be able to: describe the following electrical terms used in arc welding processes: v oltage current conductor electric arc theory open circuit voltage arc voltage duty cycle constant voltage outline the operating procedure of FCAW: electric arc semi-automated process continuous tubular wire electrode shielding gas tubular wire construction list typical industrial applications of FCAW: structural steel construction sheetmetal heavy engineering earthmoving plant mining equipment hard-facing identify metals commonly welded by the FCAW process: low carbon steels carbon manganese structural steels low alloy steels such as wear-resistant steels galvanised steels stainless steels & heat-resistant steels FCAW power sources: tr ansformer/rectif ers generators inverters power source functions: constant voltage constant wire speed coarse/f ne voltage controls polarity duty cycle 8 MEM05047B Weld using flux cored arc welding process

6 describe the functions and types of FCAW consumables: gas assisted tubular wire electrodes self-shielding tubular wire electrodes shielding gases discuss the storage and care requirements for FCAW wire electrodes: location humidity packaging list the advantages and limitations of the FCAW process: high deposition rates/eff ciency hydrogen controlled weld weld quality and penetration consumables cost site/f eld work fume generation describe the principles of distortion in relation to FCAW: heat uneven expansion & contraction job dimensions distortion control and correction methods before/during/after welding revise hazards directly associated with using FCAW equipment: electrical fumes heat arc radiation list the electrical safety requirements: welding cables clothing workshop behaviour machine location MEM05047B Weld using flux cored arc welding process 9

7 Flux Cored Arc Welding (FCAW) FCAW is an extension of the gas metal arc welding (GMAW) process in that its operating principles are similar. Other similar characteristics* include: power source functions and machine settings welding machines and welding accessories machine output and duty cycle modes of metal transfer equipment faults and weld defects In this electric arc welding process an arc is established between a continuously fed f ux cored wire electrode and the workpiece. The wire electrode is fed at a set speed from a wire spool and melts in the arc to form the weld. The wire electrode is densely packed with powdered f uxing agents which break down in the arc to form a protective gaseous shield around the weld. Droplets of weld metal and the molten weld pool are protected from the damaging effects of oxygen & nitrogen in the atmosphere by shielding gases such as hydrogen & carbon dioxide formed when the f uxing agents in the wire electrode melt. slag wire completed weld gas nozzle shielding gas FCAW Process parent metal Note: The FCAW process may use both forehand and backhand techniques depending on the wires being used. Some wires used for this process are self-shielding, which means they provide their own protective shield when they melt. Others require a secondary shielding gas such as carbon dioxide or an argon/carbon dioxide gas mixture as additional protection for the molten pool. * For detailed reading on GMAW, students should refer to the theory notes for: MEM05050B Perform routine gas metal arc welding (prerequisite unit) or MEM05017C Weld using gas metal arc welding process 10 MEM05047B Weld using flux cored arc welding process

8 wire spool drive rolls flowmeter power source (transformer/rectifier) regulator work return cable gas cylinder Student notes: contact tip gas nozzle shielding gas Diagram of FCAW/GMAW plant & equipment MEM05047B Weld using flux cored arc welding process 11

9 Basic electrical terms and definitions Several welding processes are classif ed as ARC WELDING. When the heat energy required for welding is generated by an electric arc, in most cases an arc is established between an electrode and the workpiece. It is important that welding operators have a basic understanding of arc theory and electrical terminology associated with arc welding. Electricity A form of energy associated with the movement of electrons. Conductor In welding, an electrical conductor is a metal through which electricity will easily f ow. Copper is the most used conductor, followed by aluminium. Voltage Voltage is the unit of electrical pressure. For safety reasons the voltage at the terminals of an alternating current (AC) welding machine is limited to 80 volts and 115 volts for a direct current (DC) welding machine. This electrical pressure (or force) is responsible for the current f ow in a welding circuit. Current Current (or amperage) is the measurement of the electron f ow through an electrical conductor. An ampere can be described as a unit quantity of electrical energy passing through a given point per second. This is similar to the rate water f ows through a pipeline. Theory of an electric arc An arc is generated by electrons f owing across a gap between an electrode and a metal workpiece, the electrical energy being changed into heat & light. In the case of FCAW the arc is started by depressing the welding gun trigger allowing the wire electrode to make contact with the workpiece. The f ow of electrons, that is the welding current, continues to f ow across the small gap f rst formed as an arc. The small gap has become electrically charged or ionized, and current is able to continue to f ow across the gap in the form of an electric arc. power source V voltmeter ammeter A welding cable welding gun wire electrode workpiece Basic power circuit for FCAW/GMAW 12 MEM05047B Weld using flux cored arc welding process

10 As with the GMAW process, the wire, shielding gas (when used) and current are required to form the weld. They are all activated simultaneously by the welder operating the trigger on the welding gun. When a f ux-cored wire is melted in the arc, chemical compounds are produced, due to the disintegration of f ux constituents in the wire, to form a protective slag covering on the surface of the weld. As well as protecting the cooling weld metal from atmospheric contamination, the slag covering also slows the cooling rate of the deposited weld metal. On completion of the weld, slag covering is removed by light chipping. Manufacturing process of flux cored wire electrode Flux cored wires are made by two methods, namely seamed and seamless. to wire drawing operations flux fill flux hopper strip steel closing rollers U forming rollers Improved technology in the manufacture of tubular wire electrodes has resulted in higher quality seamed wires. The availability of seamless copper coated electrode wires has resulted in better wire feeding characteristics and improved current transfer at the contact tube/tip. The use of f uxing agents inside a cored wire electrode was an early concept when arc welding was f rst utilised as a method of joining metal parts. Early diff culties of drawing tubular wire electrodes have been resolved and today manufacturers of welding consumables provide metal fabrication industries with a variety of different types & sizes of f ux cored wire electrodes. Cross-section of flux cored wires Seamless Seamed MEM05047B Weld using flux cored arc welding process 13