Physics of Welding Continued

Physics of Welding Continued

Lesson ObjectivesWhen you finish this lesson you will understand:• Wire melting modes • Power Supply Characteristics• Interactions between the arc and the power supplies• Principles of Magnetic Arc Blow

Learning Activities1. Look up

Keywords2. View Slides; 3. Read Notes, 4. Listen to lecture5. View Hi-speed

Videos6. Do on-line

workbook7. Do Excel

Tutorial

KeywordsMetal Transfer, Short Circuit Transfer, Pulsed Arc, Power Supply Characteristics, Open Circuit Voltage, Closed Circuit Current, Constant Voltage Power Supply, Constant Current Power Supply, Drooping Characteristic, Self Regulating Arc,Magnetic Arc Blow

Physics of Welding

• Heat Input Concepts• Energy Sources• Arc Characteristics• Wire Melting

GMAW Modes of Metal TransferSpray Globular

Short Circuiting Pulsed Spray

Gas Metal Arc Welding

http://www-iwse.eng.ohio-state.edu/we300/rotier.avi

Ave I

Pulsed Arc

Tandom Arc

View the Arc Welding High Speed Videos from the Video Web Page on the

WE300 Website

Turn to the person sitting next to you and discuss (1 min.):• From the chart showing the effect on metal transfer by changes in shielding gas it is seen that an addition of 2% oxygen to tan argon GMAW using DCEP caused the arc to stop wandering and have good spray transfer. Can you explain from a physical point of view what might have happened?

Welding Arcs and Machines

Open-Circuit VoltageV

I

CC

CV

Voc

Voc Hot Start

Arc

Short-Circuit CurrentV

I

(1000's)

CC

CV

Isc Isc

Arc Force or Dig

Arc

Electrical Stability of the ArcV

I

Rs

Unstable

Stable Arc

SourceArc willoperate here

Manual Arc Control

F

B

F

B

B>F F>B

h h

F

B

B=F

h

F = Feed Rate B = Burn-Off Rate

Manual Arc Control Inputs

V

I

Arc

Current Varies

h

h

Power

I

Source

Vary

V

I

Arc

Power

I

Vary Current

Source

Vary

Self-Regulation of the Arc

VmF

B

h

Contact Tube or Tip

Feed RollsWire Spoolor Reel

WireFeederCV

Power Source

V I

V

I

CV

I=F/k1

arc too

arc too short

long

current drops

current rises

F=constant, I varies

B<F B>F

Processes Using Constant Current

Processes UsingConstant Voltage

• SMAW• GTAW• PAW• Processes where humans control arc length by hand

• GMAW• FCAW• SAW• Processes that use constant velocity wire feeding

Turn to the person sitting next to you and discuss (1 min.):• In the V-I Characteristic Curves, there are two places where the Arc current and voltage are the same as the power supply current and voltage, one point is stable and the other is unstable. Why is the unstable point unstable?

Magnetic Arc Blow

Magnetic Flux Concentration

Next Class Period You will Have a Homework Assignment which will require the use of an Excel Spreadsheet. You should review your knowledge of Excel or click on the digging deeper tutorial.

Excel Tutorial