Transcript Mig Welding Notes

MIG WELDING
Arc welding as used in this unit
refers to shielded metal arc
welding(SMAW)
An electric welder and flux covered
electrodes are used
Temperature of the electric arc is
about 9, 000 degrees F
Welding area should be equipped with
metal benches
These serve both for fire protection
and to electrically ground the work
Fire extinguishers suitable for class A,
B and C fires should be available
Safety equipment and a first-aid kit
should be within easy reach at all
times
Wool fire blanket in another piece of
fire control equipment
Water spilled on the floor of the work
area must be removed seeing that it
will create an electric shock hazard
All grease, oil, paper, rags and other
flammable materials must be
removed from areas where welding
is completed
The number 10 shade lens must
always be worn when welding,
however is too dark to see through
except when the arc is burning
Wear safety glasses under helmet
All skin areas must be covered
“Sun-burning” will occur from the
rays of the arc
The method described is called the
“scratch method” of striking an arc
A bead is called a “stringer bead” if it
is made without weaving
Weaving means moving the electrode
back and forth sideways to create a
bead that is wider than normal
Beginners should lean the electrode
slightly in the direction of travel
A 75 to 80 degree angle should be
used
The arc length should sound like
bacon frying
The best method to control
movement is to watch the welded
metal solidify behind the puddle
When the speed is correct, evenly
spaced semicircles form
The first pass is called a “root pass”
The “root pass” is the most important
weld in the process
Welds made by moving horizontally
across a vertical piece of metal is
called “horizontal welding”
Low amperage results in narrow,
stringy beads
Other symptoms are:
-electrode covering turns brown
-the bead does not have clear marks
-the puddle burns through the plate
-the arc is noisy
Welding Joints:
When welding one bead or a layer of
beads this process is called a
“pass”
Welds made by moving downward
across a vertical piece of metal are
called “vertical down” welds
Welds made by moving upward
across metal are called “vertical
up”
Metal Inert Gas (MIG) welding
became popular when
manufacturers began using thingauge, high strength, low alloy
steels
In addition, it is possible to weld
aluminum castings with MIG
The MIG welding method uses a
welding wire that is fed
automatically at a constant speed
as an electrode
Since the wire is fed automatically at
a constant rate, this method is also
called semi-automatic arc welding
When the heat is sufficient to cause
the metal to melt, the process is
called “spot welding”
The device used to spot weld is
called a “spot welder”
During the welding process, either
inert or active gas shields the weld
from the atmosphere and prevents
oxidation of the base metal
For most steel welds, carbon dioxide
(CO2) is used
With aluminum, either pure argon or a
mixture of argon and helium is used
It is also possible to weld stainless
steel
MIG welding is sometimes called
carbon dioxide arc welding
The term MIG is used to describe all
gas metal arc welding processes
In fact, many welders in the industry
can use CO2 (active gas) or argon
(inert gas) by simply changing the
gas cylinder and the regulator
MIG welding uses the short circuit arc
method which is a unique method of
depositing molten drops of metal
onto the base metal
The short circuit arc method used
very thin welding rods, low current
and low voltage
Heating and cooling occurs on a
average of 100 times a second
The nozzle works as a constricting
force in the direction of the center
of the cylinder
This action is known as the “pinch
effect” and the size of the force is
called the “pinch force”
Before starting to weld, the operator
sets:
- wire speed
- arc voltage
- gas flow rate
- then presses the power button
The wire is positive and the
workplace is negative
Weld penetration is greatest using
this connection
Weld penetration is also greatest
using CO2 gas, however CO2
provides a harsher more unstable
arc
In MIG welding, the polarity of the
power source is important in
determining the penetration to the
work piece
Direct Current (DC) power sources
used for MIG welding typically use
DC reverse polarity which leads to
increased spatter
It is preferable to use argon/CO2
PLASMA ARC CUTTING
Plasma- fluid portion of blood found in
region of electrical chargedischarge (arc)
Ionized Gas- plasma created by an arc
Both electrons and
positive ions whose
charges are nearly equal
to each other
Plasma results when a gas is heated
to a high enough temperature to
convert into positive and negative
ions-11, 000 to 23,000 degrees F
Arc Plasma- defined as a gas that has
been heated to at least a
partially ionized
condition
Plasma arc- used to refer to the arc
plasma used in welding
and cutting processes
* Produces both high
temperature and intense light
* Arc welding like cutting
Plasma torch- creation & control of the
plasma for welding or
cutting
Torch body- special plastic-resistant to
high temperaturesultraviolet light and
impact
*available in variety of lengths and
sizes
Generally the longer, larger
torches are used for the higher
capacity machines
Body is called a “barrel”
Torch Head- angles 75-90-180
cooling for low power torches may
either be by air or water
Power Switch- variety of options
Electrode Setback- spacing between
electrode tip and nozzle tip critical
for proper operation
Nozzle tip- small, cone shaped,
constricting orifice in the center
Space between the electrode tip and
nozzle tip is where the electric
current forms the plasma
Nozzle- referred to as the “cup”
* made of ceramic
* high temperature resistant
substance
Common Torch Parts:
-electric tip
-nozzle insulator
-nozzle tip
-nozzle guide
-nozzle
The torch parts are made of copper
Electrode tip- made of copper with
tungsten tip-keeping tip cools,
lengthens the life of the tip and
allows better quality cuts for longer
period of time
Nozzle insulator- between electrode
tip and nozzle tip
Gas Hose- 2 types of hoses-1 hose
carries gas used to produce plasma
and one produces a shielding gas
coverage
Central wire- 2 conductors-low
voltage stranded copper wire
connects power switch to power
supply
Water tubing- medium/high amperage
torches may use water-failure to use
de-ionized water will result in the
torch arching out internally
Water Shroud- water surrounding the
tip is used to control the hazards of
light, fumes and noise
Power and Gas cables- power cablehigh voltage rated insulation made
of finely stranded copper wire to
allow for maximum flexibility
Power Conductors- positive &
negative-size and current carrying
capacity of this cable is a
controlling factor to the power
range of the torch
Voltage- production of plasma
requires a drooping arc voltage or
constant current
direct current high voltage power
supply-this allows for a rapid start
of the plasma arc at the high open
voltage
Amperage- flow is much lower than
with most welding processes-PAC
torches operate on 10 amps-the
higher the amperage capacity the
faster & thicker they will cut
Stack Cutting- sheets of steel
Dross- metal compound that resolidifies & attaches itself to the
bottom of a cut-made up of unoxidized metal
Water table- used to reduce the noise
level, control the light, trap sparks
and eliminate fumes
Plasma arc gouging- similar to air
carbon arc gouging
Safety Hazards: light-fumes-sparkselectrical shock-moisture-noise
Heat Input- Jouls-per inch of heat the
cut will receive-work per linear foot
Distortion- metal is heated and
moves (bends) up towards the heat,
while the metal is cooled moves
( bends) away from the heated area
Heat Affected Zone- area heated for
work
PAC- Plasma Arc Cutting
Cutting Speed- high-25 feet per
minute-1/4 mile per hour
Standoff distance- distance from the
nozzle tip to the work-distance is
crucial for quality cuts
Starting Methods- most common type
is high frequency, alternating
current
Pilot air- arc between the electrode
tip & the nozzle tip within the torch
head
Kerf- space left in the metal as the
metal is removed during a cut
Factors for Success:
-standoff distance -gas used
-orifice diameter
-travel speed
-power setting
-water injection
-swirling of gas
-electrode tip
Factors that affect the cut by
changing the gas:
-force -heat content
-central concentration
-kerf width
-dross formation
-top edge rounding -metal type
HAPPY WELDING & CUTTING