Transcript GMAW Slides

GMAW Process and Set Up
Atwater High School Ag Shop
Meredith
Introduction
• GMAW - gas metal arc welding (often called
MIG: metal inert-gas) is done by using a
consumable wire electrode to maintain the
arc and to provide filler metal. The wire
electrode is fed through the torch or gun at a
preset controlled speed. At the same time, an
inert gas is fed through the gun into the weld
zone to prevent contamination from the
surrounding atmosphere.
Introduction
Introduction – Short Arc Transfer
• We use a process called Short-Arc Transfer.
This process allows the electrode to contact
the weld pool and causes a “short circuit”.
This allows the electrode to be pinched off
and deposited in the molten puddle. This
buildup becomes your weld. 50-200 times per
second
Short Arc Transfer
Short Arc Transfer
• Short Circuit Transfer Video
Introduction - Globular Transfer
• Welding current and wire speed are increased
above maximum for short arc
• Droplets of metal have a greater diameter
than the wire being used
• Spatter present
• Welding is most effectively done in the flat
position when using globular transfer
Globular Transfer
Globular Transfer
• Globular Transfer Video
Introduction - Spray Transfer
• Occurs when the current and voltage settings
are increased higher than that used for
Globular Transfer
• Used on thick sections of base material, best
suited for flat position due to large weld
puddle
• Spatter is minimal to none
• Spray Transfer is the hottest weld
Spray Transfer
Spray Transfer
Spray Transfer
• Spray Transfer Video
Introduction – Polarity
• Almost all GMAW welding is done with Reverse
Polarity
• DC+ or DCEP (Direct current Electrode Positive)
Advantages of GMAW Welding
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Arc visible to the operator
High welding speed (faster)
No slag to remove
Sound welds / High Weld Quality
Large gaps can be filled easily
Less distortion to the work piece
Weld in all positions (transfer type)
• In welding, as in most jobs, exposure to
certain hazards occurs. Welding is safe when
precautions are taken. The safety information
given in your handout is a summary and
should be considered as the “basics” you need
to know in order to operate welding
equipment safely. You will be tested on this
information to insure adequate knowledge
has been achieved.
Personal Safety Equipment
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1. Welding helmet - shade 10 min.
2. Gloves
3. Coveralls/protective clothing
4. Boots - Pants/coverall legs slide over boot
tops
Equipment - Voltage
• Welding Machine - A specially designed
welding machine is used for MIG welding. It is
called a constant voltage (CV) type power
source. This means that the output welding
power of a CV machine is about the same
voltage regardless of the welding current.
Equipment – Variables
• The output voltage is regulated by either a
rheostat (Miller 250, 251) or voltage selector
switch (Miller 252, 350P, XMT and Lincoln 255)
• The current on all machines is determined by
wire speed.
• Wire speed = rate at which wire is deposited
into the weld pool in inches per minute (IPM)
Equipment – Wire Speed
• Allows you to vary both the speed of the wire
feed and the weld current. Displayed in IPM or
percents
• Rotating the wire speed control knob clockwise
increases the wire speed.
• The scale around the control is in percents and
does not indicate actual wire speed. Need to
ratio the percent to find actual IPM.
• On the 22A wire machines, 10% = 75 IPM
• On the Lincoln 255 and Miller 250s the wire
speed is actual IPM
Equipment – Ground Clamp
• Attach ground clamp to clean metal
• Attach as close
to weld as
possible
Equipment – Machine Power Switch
• Used to turn the unit ON or OFF. Some units
also have a pilot light or a fan will be on.
• A fan will only operate when cooling is
required.
Equipment – Torch / Gun
When the trigger is pressed on the gun, the
following happens:
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- wire feeds
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- gas flows
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- welder is energized
Equipment – Torch / Gun
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1 – Neck or connector tube
2 – Insulator
3 – Gas Diffuser
4 - Contact Tip
5 - Nozzle
Equipment – Shielding Gas
• Cylinder - contains CO2, Argon, or a mix of
both as the shielding gas. Open valve on
cylinder just before welding.
• CO2 – Carbon Dioxide - Inert Gas, stable
sound welds and is more economical
• Argon – Inert Gas, heavier, increased arc
penetration and expensive
• 75/25 - Argon / CO2 – Blended
• 90 / 10 (or) 92 / 8
Equipment – Cylinders
Pure and Mixed Gases
Equipment – Shielding Gas
• Regulator – reduces high pressure into a lower
working pressure. Measured in CFH’s (cubic
feet per hour) on inert gas cylinders. Set at 25
CFH
• Flow Meter - controls the flow of gas and is
measured in CFH’s (cubic feet per hour). Set at
25 CFH.
Regulator
Flow Meter
Operation - Variables
• Variables - The applied techniques and end
results in the MIG welding process are
controlled by variables which must be
understood by the student. These variables
include adjustments made to the equipment
and manipulations made by the operator.
• These include pre-selected supplies, machine
controls or adjustments, and operator motion
Preselected Variables
• Depend on the type of material being welded,
thickness, position, and deposition rate. They
include:
• type of wire
• size of wire
• type of gas
• gas flow
Primary Adjustable Variables
• control the process after preselected
variables have been found. They control
penetration, width, height, deposition rate,
and weld soundness. They include:
• arc voltage
• welding current
• travel speed
Secondary Adjustable Variables
• cause changes in the primary adjustable
variables which results in changes to bead
formation. They are:
• stick out 1/4” - 3/8”
• nozzle angle
• wire speed
Types of Joint Fit Up
Welder Set Up
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1. Plug unit into power source.
2. Make sure the joint to be welded is clean.
3. Connect ground clamp to work piece.
4. Set up welding machine:
- turn on shielding gas at the source (set between
25 CFH)
- turn on power switch
- set voltage and wire speed according to the
chart inside welder
- will depend on metal type and thickness
Welder Set Up Cont.
• 5. Put on appropriate safety gear.
- gloves
- welding hood (min. #10 lens)
- protective clothing
• 6. Run practice bead on scrap metal that is similar to
actual work.
• 7. Weld spatter should be minimal and the arc should
sound like ripping cloth or frying bacon.
• 8. Fine tune welder as needed.
- adjusting the wire speed will change the amperage
Welder Shut Down
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Stop welding.
Turn off power source, roll up cords.
Turn off shielding gas at the source.
Roll up ground cable and gun.
Return Welder to original place kept.
CLEAN UP AFTER YOURSELF!!!