Download Weld using flux cored arc welding process

Weld using flux cored arc
welding process
(MEM05047B)
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T5$,1,1*$1'('8&$7,216833257
INDUSTRY SKILLS UNIT MEADOWBANK
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LEARNING RESOURCE MANUAL
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Metal Fabrication & Welding
MEM05047B/1
First Edition
Product Code: 2966
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.
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Cigweld Pty Ltd
Lincoln Electric (Aust) Pty Ltd
ESAB
Welding Industries Australia (WIA)
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Copyright acknowledgments:
MEC&T Curriculum Centre would like to acknowledge the assistance and permission of the following
companies for the use of copyright material:
978 0 7348 2716 6
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) 9942 3200
Fax: (02) 9942 3257
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
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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
First Edition - March 2008
© MEC&T Curriculum Centre, TAFE NSW
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Theory
MEM05047B Weld using flux cored arc welding process
First Edition - March 2008
© MEC&T Curriculum Centre, TAFE NSW
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Flux cored arc welding operating principles
Objectives:
At the end of this unit you will be able to:
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oltage
current
conductor
electric arc theory
open circuit voltage
arc voltage
duty cycle
constant voltage
outline the operating procedure of FCAW:
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electric arc
semi-automated process
continuous tubular wire electrode
shielding gas
tubular wire construction
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list typical industrial applications of FCAW:
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describe the following electrical terms used in arc welding processes:
structural steel construction
sheetmetal
heavy engineering
earthmoving plant
mining equipment
hard-facing
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identify metals commonly welded by the FCAW process:
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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:
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ansformer/rectif ers
generators
inverters
power source functions:
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constant voltage
constant wire speed
coarse/f ne voltage controls
polarity
duty cycle
MEM05047B Weld using flux cored arc welding process
First Edition - March 2008
© MEC&T Curriculum Centre, TAFE NSW
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discuss the storage and care requirements for FCAW wire electrodes:
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location
humidity
packaging
list the advantages and limitations of the FCAW process:
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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:
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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
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gas assisted tubular wire electrodes
self-shielding tubular wire electrodes
shielding gases
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describe the functions and types of FCAW consumables:
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list the electrical safety requirements:
welding cables
clothing
workshop behaviour
machine location
MEM05047B Weld using flux cored arc welding process
First Edition - March 2008
© MEC&T Curriculum Centre, TAFE NSW
9
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:
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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.
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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.
gas nozzle
wire
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slag
shielding gas
completed weld
parent
metal
FCAW Process
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
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MEM05047B Weld using flux cored arc welding process
First Edition - March 2008
© MEC&T Curriculum Centre, TAFE NSW
wire spool
drive rolls
flowmeter
regulator
power source
(transformer/rectifier)
gas cylinder
work return cable
contact
tip
gas
nozzle
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shielding
gas
Student notes:
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Diagram of FCAW/GMAW plant & equipment
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MEM05047B Weld using flux cored arc welding process
First Edition - March 2008
© MEC&T Curriculum Centre, TAFE NSW
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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
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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
Theory of an electric arc
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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.
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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
welding cable
ammeter
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welding gun
wire electrode
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voltmeter
workpiece
Basic power circuit for FCAW/GMAW
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MEM05047B Weld using flux cored arc welding process
First Edition - March 2008
© MEC&T Curriculum Centre, TAFE NSW
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.
strip steel
flux fill
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flux hopper
“U forming” rollers
to wire drawing
operations
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closing 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
First Edition - March 2008
© MEC&T Curriculum Centre, TAFE NSW
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