Download Physics of Welding Module 2

Physics of Welding Continued
Physics of Welding Continued
Lesson Objectives
When 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 Activities
1. Look up
Keywords
2. View Slides;
3. Read Notes,
4. Listen to lecture
5. View Hi-speed
Videos
6. Do on-line
workbook
7. Do Excel
Tutorial
Keywords
Metal 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
Gas Metal Arc Welding
GMAW Modes of Metal Transfer
Spray
Globular
Short Circuiting
Pulsed Spray
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 Voltage
V
CC
Voc
Hot Start
Arc
CV
Voc
I
Short-Circuit Current
V
CC
Arc Force
or Dig
CV
Arc
I
Isc
Isc
(1000's)
Electrical Stability of the Arc
V
Unstable
Rs
Stable
Arc will
operate here
Arc
Source
I
Manual Arc Control
F
F
F
B
h
B
h
B=F
B
h
F>B
F = Feed Rate
B = Burn-Off Rate
B>F
Manual Arc Control Inputs
Vary
I
V
I
V
Power
Source
Power
Source
Vary
h
Arc
Arc
h
I
Vary Current
I
Current Varies
Self-Regulation of the Arc
Wire Spool
or Reel
Feed Rolls
V
I=F/k1
Contact
Tube or Tip
F
CV
Power
Source
I
Vm
Wire
Feeder
B
arc too
long
CV
V
arc too
short
h
F=constant, I varies
current
drops
B<F
current
rises
B>F
I
Processes Using
Constant Current
• SMAW
• GTAW
• PAW
• Processes
where humans
control arc
length by hand
Processes Using
Constant Voltage
• 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