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Lecture 6
Welding Processes
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Welding Power Supplies& Controls
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Lecture Scop_e _
• Power Supply Output Characteristics
• Relationship to Welding Processes
• Main Types of Power Supply- Transformer- Solid state- Alternator
• Process Controls
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Lecture 6
"Drooping" Output Characteristic
BOV Open Circuit Voltage
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i !lOA -...i! Change in Current
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150 A Maximum Current
CURRENT (AMPERES)
"Flat" Output Characteristic
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Open Circuit Voltage 30 V r=--=::C:~J~L~o:ng~N~C;_~~~~ShortNCChange in Voltage 5 vI _-.-! _ _ _ _ _ -
I ~, II ,i Change in Current I, 100A iI • • ,
100A 200 A
. CURRENT (AMPERES)
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Combination Volt-Amp Curve
wC)
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Lecture 6
CURRENT (AMPERES)
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Principal Elements ofTransformerPowerSu~ __
N1 N2TURNS TURNS
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ARC
C
ACOUTPUT
A
,--_JMETAL CORE
TRANSFORMERA: Primary solid state inverter if usedB: Series output control if used (AC/DC)C: Rectifier or SCR control for DC outputD: Secondary switch for chopper type control of DC output
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Moveable-Coil AC Power SourcePRIMARY
COIL
IRONCORE
SECONDARYCOIL
v MINIMUMOUTPUT
o 50 100 1m 200 250
A
lecture 6
80
v
G 50 100 150 200 250
A
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.Jlpical Series Impedance Control (
Exr~?~r.~9.~...r:>~?P., --
-,, i SERIES i! 1 !' IMPEDANCE i t,, i. ..............___...........__.......__.li
ERI Output Arc
Voltage Voltage ARC
1 Eo EA,,~ +
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•
[..__ __ .1
...............__ - __ ..,: .,,,!TRANSFORMj,,i •
•1AC
InputVoltage
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Moveable-Core Reactor ACPower Source
POSITION FOR POSITI6N FORMINIMUM CURRENT MAXIMUM CURRENT
lecture 6
PRIMARYCOil
TRANSFORMER
ELECTROD
SECONDARYCOil
I L-_-..l..../.... -----"'""'1/
MAGNETIC FLUX PATH
STATIONARY SECTION
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Saturable Reactor AC WeldingPower Source (
c ..ROL
I --- I I I I T\ \ T
AIR GAP ·rt = . AIR GAP
I \ I , I , I
I- - ELEcTRODE]- - --Iw_..... -
e>-,...j WORK I
DCCONT
WELDINGTRANSFORMER
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6 P 10
Magnetic Amplifier Control+
DINGRODE
OL
CONTROL INPUT l~- Lr' I I ,
-
fl., \\\ , -
OIO~E T i>~..CONTR
I Ie - COILS
~'~J VRANSFORMER WEL
\ I I ELECT'-- - . I .,
Y - - AC SECOt:!OARY- I0- - -Iw- WORK
T
DC
ACPRIMAR
Lecture 6 P 11
AC Current Waveforms
ELECTRODE NEGATIVE
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ELECTRODE POSITIVE
ELECTRODE NEGATIVE
ELECTRODE POSITIVE
A-Magnetic AmplifierB-Square Wave
A
B
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Phase Control Using an SCR BridQ!
..c:~::ro TIme
High-power SCRs conducting early in the half-cycle
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,--..../' \ .•I• TIme
Lecture6
Lower power SCRs conducting late in the half-cycle
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SCR-Controlled DC Power Source (
1 - +
DC ARC
1OUTPUT
jAC
INPUT
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6 p14
Inverter Power Source
+
utput- 1-.-
]~-«- ~~ -- -cI- LuJ 0
- I--
InverterCon1rOlCircu~
~oN\~ ~ JllIIlll o~'_OUTPUT
INPUT BRIDGE BRIDGERECTIFIER INVERTER TRANSFORMER RECTIFIER INDUCTOR
ACINPlIT
Lecture 6 P 1,
Alternator TY'pe Power SUe.e!Y__ (
6
AC HERE
IIIIM...-..rFINE CURRENT CONTROL
COARSE CURRENT·CONTROL(TAPPED REACTOR)
DC OUTPUT
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Process Controls
• Welding Current Programming- upslope, downslope, crater fill
• Process cycle control- co-ordinate operation of welding power, wire feed, weld
head motion, shielding gas flow, etc- Open loop logic
• Adaptive or feedback control- seam tracking
~ arc voltage control, electro-mechanical & opticalmethods
- process control
Lecture 6 p1
Current Programming _
Pulsed GTAW
pulse duration 0.1 - 1sec
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Peak,-- ~ 00 current
~.I'ho~~ Background
'-- ---.J l.... current
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TIME
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Process Control
Component Status Weld Cycle TIme
Lecture 6
SEAMTRACKER
TURNTABLE
WELDINGEQUIPMENT
Weld overtap
Tracking
Drive InlO~
Idle
Motion
Idle
Welding ClOTenl
Shield gas flow
Idle
Cycle start, Cycle end,
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Adaptive Control
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Input Welding ~ Outputvariables Process variables
Feedback Loop
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Adaptive control
Arc length control based on arc voltage
Lecture 6
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Adaptive ControlJoint tracking using arc voltage sensing
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--- .. - -----
Adaptive control
Optical joint tracking methodVldlo SIOllOI 10
,'-'...... 1oI0chlni lillian Sylt.m
\ ~;;:;;~:n~om.,o \. [JU
~-INarraw Band ....." Int.rfer.nce FllIlr "-
.-Comlra ....",;==='-'I Optic AILII Monitor'V"'.-'
C,llnclrlca1Lenl
Struclurad L10h(Laee, Plalllle:::~~Q.
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Adaptive control
Feedbackcontrol ofGTAWweldpenetrationbased onphotodiodes
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