Welding 1-6

Welding - Definition
CVEN 485 - Spring 2005
Fundamentals
of
Welding
Welding Processes – Steel
9 Oxyfuel Gas
9 Electric Arc
9 Friction
9 Resistance
9 Casting
Governing Code - Steel
American Welding
Society – AWS
D1.1 – Structural
Welding Code - Steel
Materials joining process used in making
welds
Weld - Definition
Localized coalescence of metals or nonmetals produced by heating the material to
suitable temperatures, with or without the
application of pressure, and with or
without the use of filler metal
Electric Arc Welding
9 Shielded Metal Arc Welding (SMAW)
9 Flux Cored Arc Welding (FCAW)
9 Gas Metal Arc Welding (GMAW)
9 Gas Tungsten Arc Welding (GTAW)
9 Submerged Arc Welding (SAW)
Arc Welding Process Components
9 Power Source (modifies and controls
input electrical current)
9 Electrode (consumable or nonconsumable)
9 Shielding (gas or solid that forms gas
as it burns)
1
Electrical Current
Flow of Electrons
W=VxA
Arc Welding
Voltage Potential
Between Electrode
and Base Plate
Gap
Electrode
W = Wattage – measure of work (controls the
width and depth of weld bead)
Arc
Base Plate
Types Arc Welding Current
1. Alternating Current (AC)
2. Direct Current – Straight Polarity
(DCSP)
3. Direct Current – Reverse Polarity
(DCRP)
A power source is either AC or both DCSP
and DCRP
Arc Stabilization
Important that the current flow is stable so that
a uniform and consistent weld is formed.
V = Voltage – measure of electrical pressure
(controls maximum length of arc across gap)
A = Amperage – measure of the rate of flow
of electrons (controls size of the arc).
Arc Temperature
Approximately 9000ºF – HOT!!!!
Affected by the resistance to the current flow.
Resistance – a function of the arc length and
the chemical composition of the gases formed
or introduced during the welding process.
Increasing the gap, increases the resistance,
which increases the temperature. The reverse
is also true.
( Constructional steel melts at approx. 2800°F )
Straight Polarity – DCSP
(Electrode Negative (DCEN))
Electrode
(negative,
cathode)
More heat at base plate
(greater penetration)
-
Modern day power supplies are often digitally
controlled.
-
-
-
-
1/3 Heat
-
-
Shielding gases are used to stabilize the arc in
addition to protecting the weld pool from the
atmosphere.
Base Plate
(Positive,
anode)
2/3 Heat
2
Straight Polarity - DCSP
Reverse Polarity – DCRP
(Electrode Positive (DCEP))
Electrode
(Positive,
anode)
More heat at electrode
(greater deposition)
-
-
-
-
-
+
2/3 Heat
-
-
Reverse Polarity - DCRP
+
Base Plate
(Negative,
cathode)
More heat at
base plate
(greater
penetration)
More heat at
electrode
(greater
deposition)
-
1/3 Heat
Arc Blow
Arc Blow
The deflection of an electric arc from its
normal path because of magnetic forces.
Uneven magnetic flux lines can cause an arc to
move during a weld.
More noticeable in corners, at ends of plates, when
the work (ground) lead is connected to only one
side of the of a plate, or if the plate has been
magnetized.
(Not a problem with AC current.)
Types of Welds
9 Fillet Weld
9 Complete Penetration Groove Weld
Fillet Welds
Fillet welds generally are the simplest and least expensive
welds to fabricate. Therefore, preference should be given to
this weld type. The weld is produced by depositing weld
metal at the corner formed by intersecting or lapping plates.
9 Partial Penetration Groove Weld
9 Plug and Slot Weld
3
Complete Joint Penetration Groove
Welds (CJP)
Partial Joint Penetration Groove Welds
(PJP)
Full or complete joint penetration groove welds can be used
in application were maximum strength of the connection is
required. The weld is produced by cutting or grinding a
chamfer or bevel on the edge of the plate(s).
Partial joint penetration groove welds are similar to
complete penetration welds in that the plate edges are
beveled prior to welding. However, the finished weld does
not fully penetrate the plate thickness due to reduced
strength requirements.
Plug and Slot Welds
SMAW – Shielded Metal Arc Welding
These types of welds are used to connect lapped plates.
Either a circular (plug) or rectangular (slot) hole is cut into
one of the plates. The plates are then lapped and the hole
filled with weld metal.
FCAW – Flux Cored Arc Welding
SAW – Submerged Arc Welding
Nozzle
Slag
Weld
Electrode
Wire
Flux
GMAW – Gas Metal Arc Welding
Base Material
Molten Pool
4
SAW – Submerged Arc Welding
Welding Parameters
9 Current (Voltage/Amperage)
9 Travel (Wire) Speed
9 Electrode (solid or flux-cored)
9 Shielding gas
MIG – Welding
Metal Inert Gas
Shielding Gases
9 Argon (Ar) – Provides a stable arc, high density
gas envelope (difficult to disturb).
MIG welding equipment can perform both
FCAW and GMAW welding.
9 Carbon Dioxide (CO2) – Less expensive than Ar
but less dense. Greater heat conductivity.
FCAW uses a flux-cored wire. No additional
shielding gas is required.
9 Mix – 75% Ar / 25% CO2 – Compromise in
density and heat conductivity.
GMAW uses a solid wire but must be used in
conjunction with a shielding gas.
9Helium (He) – Result in an unstable arc, low
density gas envelope. Expensive
MIG Solid Wire Welding
9 Must be used with CO2 or 75% Ar / 25% CO2
shielding gas.
9 CO2 is economical and results in deeper penetration.
MIG Flux-Cored Wire Welding
9 No shielding gas required. Provide as the flux in
the core of the wire vaporizes.
9 Can use outdoors in windy conditions.
975% Ar / 25% CO2 has less splatter and better bead
appearance.
9 Good with dirty, rusted, and painted materials.
9 Indoor use, no wind.
9 Runs hotter than solid wire, limited to 18 gauge and
thicker.
9 Can weld relatively thin material (22 guage).
5
Polarity Settings
GMAW
FCAW
MIG Power Supply
AC input current is converted to DC using
rectifiers.
A Rectifier allows current to flow in only one
direction. A series of rectifiers are used to
provide a constant DC current.
More Heat at
Electrode
More Heat at Base
Plate
Heat is generated and lost in the rectifiers
making DC welding less efficient than AC
Welding.
MIG Power Supply
Millermatic 185 Control Panel
1. Wire Speed Control
A transformer is used to step-down the
voltage of the input current (and increase the
amperage).
Use control to select a wire
feed speed. Scale around
control is not actual wire feed
speed, but is for reference only.
Can switch while welding.
Input current is 230V and 26A. Output
current is transformed according to the
Voltage-Amperage Curves.
2. Voltage Switch (TAP)
The higher the selected
number, the thicker the material
that can be welded. Do not
switch while welding.
Curves given for each TAP (transformer)
setting.
3. Power Switch
Transformer with Taps
Volt-Amperage Curves
Iron Core
Primary Coil
Secondary Coil w/
TAPS
INPUT
230V x 26A =
5980W
Millermatic 185
OUTPUT
23V x 150A =
3450W (TAP6)
Note that Wattage is lost during rectifying and transformation.
6
Circuit Diagram
Current versus Volt-Amperage
Millermatic 185
As you increase the gap, you increase the
resistance, which increases the voltage and
decreases the amperage.
You cannot have precise voltage and/or
amperage settings on the welding unit.
Too low a current setting will not give you
enough penetration. Too high a current
setting will cause burn-through in the plate.
Power Source Duty Cycle
Percentage of time
that unit can weld at
rated load without
overheating (of
transformer and
rectifiers).
MIG - Wire Size / Current Set
Wire Size
Amperage Setting
0.023 inches
30 – 90 A
0.030 inches
40 – 145 A
0.035 inches
50 – 180 A
Millermatic 185
Selecting Wire and Shielding Gas
MIG Welding
Millermatic 185 – Mild Steel
Solid Wire
ER70S-6
Flux Core
E71T-GS
100% CO2
20 cfh
75/25%
Argon/CO2
20 cfh
No Shielding
Gas Required
0.023 inches
0.030 inches
0.035 inches
0.023 inches
0.030 inches
0.035 inches
0.030 inches
0.035 inches
0.045 inches
7
Selecting Wire and Shielding Gas
Example of Good and Bad MIG Welds
Millermatic 185 – Mild Steel
100% CO2
75%/25%
Good
Weld
Flux Core
Travel
too fast
Travel
too slow
Voltage
too low
Voltage
too high
Wire
Speed
too low
Wire
Speed
too high
Poor Weld Bead Characteristics
Troubleshooting – Excessive Splatter
Good Weld Bead Characteristics
Troubleshooting – Porosity
Troubleshooting – Excessive Penetration
8
Troubleshooting – Lack of Penetration
Troubleshooting – Incomplete Fusion
Troubleshooting – Excessive Splatter
Troubleshooting – Distortion
Troubleshooting – Waviness of Bead
Electrode Manipulation
Weave Patterns
Movement of the electrode during welding
will affect characteristics of the weld bead,
such as:
• Buildup
• Width
• Penetration
• Defects – porosity, undercut, overlap,
and slag inclusions
9
MIG Gun Angle
10