Lecture 6

Welding Processes

- .

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

,

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,,~ +

,,,

•

[..__ __ .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

..c:~c3

,--..../' \ .•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

I Z

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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

-L

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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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