Welding Processes
- .
Welding Power Supplies
& Controls
Lecture 6 p
Lecture Scop_e _ (
• Power Supply Output Characteristics
• Relationship to Welding Processes
• Main Types of Power Supply
- Transformer
- Solid state
- Alternator
• Process Controls
p2
"Drooping" Output Characteristic
BOV Open Circuit Voltage
,
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lOA -...i!
, I
Change in Current
150 A Maximum Current
CURRENT (AMPERES)
Lecture 6
"Flat" Output Characteristic (
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vI r=--=::C:~J~L~o:ng~N~C;_~~~~
rtNC
Open Circuit Voltage 30 V
Change in Voltage 5 _-.-! _ _ _ _ _ Sho -
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i Change in Current I
,
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100A i
• ,
100A 200 A
. CURRENT (AMPERES)
p4
Combination Volt-Amp Curve
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CURRENT (AMPERES)
Lecture 6 p~
Principal Elements of
TransformerPowerSu~ __ (
N1 N2
TURNS TURNS
A C
AC
ARC
OUTPUT
,--_J
METAL CORE
TRANSFORMER
A: Primary solid state inverter if used
B: Series output control if used (AC/DC)
C: Rectifier or SCR control for DC output
D: Secondary switch for chopper type control of DC output
,6 p6
Moveable-Coil AC Power Source
PRIMARY
COIL
IRON
MINIMUM
CORE v
OUTPUT
SECONDARY
COIL o 50 100 1m 200 250
A
80
v
G 50 100 150 200 250
A
lecture 6 p'
.Jlpical Series Impedance Control (
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r i
Ex
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SERIES i
-
-
•1 ,, 1 !' IMPEDANCE .li
i...............___...........__.......__ t
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AC Output Arc
Input !TRANSFORMERI Voltage Voltage ARC
Voltage ,1,, Eo EA
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[..__ __ .1
p8
Moveable-Core Reactor AC
Power Source
POSITION FOR POSITI6N FOR
MINIMUM CURRENT MAXIMUM CURRENT
TRANSFORMER
PRIMARY SECONDARY
COil COil
I L-_-..l..../
.... -----"'""'1/
MAGNETIC FLUX PATH
ELECTROD
STATIONARY SECTION
lecture 6 p!
Saturable Reactor AC Welding
Power Source (
DCCONTROL
c ..
-
I -
- I I I I T\ \ T
AIR GAP ·rt I \ I , I , I
= . AIR GAP
I
--..... --
e>-
,...j
- --Iw_ ELEcTRODE]
WORK I
WELDING
TRANSFORMER
6 P 10
Magnetic Amplifier Control
+
DC CONTROL INPUT l~
-
Lr' I I ,
fl.,T \\\ , -
-
i>~
OIO~E
.. CONTROL
I Ie - COILS
TRANSFORMER
~'~J V WEL DING
ACPRIMARY --
'-- -- .
AC SECOt:!OARY
I
\ I I
.,
ELECTRODE
I
0- - -Iw- WORK
Lecture 6 P 11
AC Current Waveforms (
ELECTRODE NEGATIVE
A
ELECTRODE POSITIVE
ELECTRODE NEGATIVE
B
ELECTRODE POSITIVE
A-Magnetic Amplifier
B-Square Wave
,6 P 12
Phase Control Using an SCR BridQ!
..
c:
~::r
o TIme
High-power SCRs conducting early in the half-cycle
..
c: /'
,--....
\.
~ •
I
c3 • TIme
Lower power SCRs conducting late in the half-cycle
Lecture6 p13
SCR-Controlled DC Power Source (
- +
1
DC ARC
OUTPUT
1
AC
j
INPUT
I Z
6 p14
Inverter Power Source
~oN\ ~ ~ JllIIlll o~'_
OUTPUT
INPUT BRIDGE BRIDGE
RECTIFIER INVERTER TRANSFORMER RECTIFIER INDUCTOR
AC -
INPlIT
-
-«-
1-.-
~~
-- I-- ]~ -cI- LuJ 0
+
utput
Inverter
Con1rOl
Circu~
Lecture 6 P 1,
Alternator TY'pe Power SUe.e!Y_ _ (
COARSE CURRENT·
CONTROL
(TAPPED REACTOR)
AC HERE
IIIIM...-..r-
FINE CURRENT CONTROL DC OUTPUT
{
,
6 p16
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 & optical
methods
- process control
Lecture 6 p1
Current Programming _ (
Pulsed GTAW
pulse duration 0.1 - 1 sec
Peak
,-- ~ 00 current
~.I'ho
~~ Background
'-- ---.J l.... current
TIME
,6 p18
Process Control
Component Status
SEAM
Weld overtap
Tracking
,
Cycle start
Weld Cycle TIme
,
Cycle end
TRACKER
Drive InlO~
Idle
Motion
TURNTABLE
Idle
Welding ClOTenl
WELDING
EQUIPMENT Shield gas flow
Idle
Lecture 6 pH
Adaptive Control (
-
-
Input
variables <r Welding
Process
~ Output
variables
Feedback Loop
l p20
Adaptive control
Arc length control based on arc voltage
L
-
Lecture 6 p2
(
Adaptive Control
Joint tracking using arc voltage sensing
p22
- - - .. - -----
Adaptive control
Optical joint tracking method
Vldlo SIOllOI 10
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~-INarraw
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Band
Int.rfer.nce FllIlr
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C,llnclrlca1
Lenl .-Comlra ",;==='-'
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Struclurad L10h
I
'V"'.-'
Optic AILII Monitor
(Laee, Plalllle:::~~Q.
p23
(
Adaptive control
Feedback
control of
GTAWweld
penetration
based on
photodiodes
p24
