Gas Metal Arc Welding GMAW Section 8 Unit 26 - PowerPoint PPT Presentation

Loading...

PPT – Gas Metal Arc Welding GMAW Section 8 Unit 26 PowerPoint presentation | free to view - id: d829-OWIzM



Loading


The Adobe Flash plugin is needed to view this content

Get the plugin now

View by Category
About This Presentation
Title:

Gas Metal Arc Welding GMAW Section 8 Unit 26

Description:

Stickout is the distance from the end of the contact tube to the weld surface. Insufficient stickout will cause the wire to fuse to the contact tube. ... – PowerPoint PPT presentation

Number of Views:1202
Avg rating:3.0/5.0
Slides: 34
Provided by: harry2
Category:
Tags: gmaw | arc | gas | metal | section | tube | unit | welding

less

Write a Comment
User Comments (0)
Transcript and Presenter's Notes

Title: Gas Metal Arc Welding GMAW Section 8 Unit 26


1
Gas Metal Arc Welding (GMAW) Section 8 Unit 26
2
Introduction
  • GMAW is an arc welding processes.
  • Same three requirements
  • Also known as Metal Inert Gas (MIG).
  • Sometimes referred to as semiautomatic arc
    welding
  • It was developed for production welding
  • More difficult than SMAW to switch sizes of metal
    and types of metal.
  • GMAW is best process for welding thin steel

3
GMAW Safety
  • Follow manufacturers recommendations
  • Check all cables
  • Wear appropriate PPE
  • Never touch electrical or welding wire when the
    switch is on.
  • Never weld in wet locations or when wet.
  • Use pliers for hot metal
  • Insure adequate ventilation.
  • Have machine repaired by competent person.
  • Turn off and safety store welder when done
    welding.

4
Introduction
  • The three requirements of fusion welding and how
    GMAW meets these requirements.

Heat
Shielding
Filler Material
Process
Outer Envelope
Manual Rod Or Base Metal
OFW
Flame
Electric Arc
Inert Gas from flux
Manual Electrode
SMAW
Inert Gas from cylinder
Continuous wire Electrode
Electric arc
5
GMAW Process
  • A continuous wire electrode from a spool or coil
    is pushed by the wire feeder through a flexible
    conduit to the welding gun.
  • The wire exits the welding gun through the
    contact tip.
  • A constant potential power supply supplies the
    current for an electrical arc that is hot enough
    to melt the base metal and the electrode.
  • The wire melts and combines with the molten base
    metal to form a weld.
  • Shielding is provided by an inert gas supplied by
    a cylinder
  • Gas flow is controlled by a solenoid valve and is
    delivered to the nozzle on the gun.

6
GMAW System Parts
Cylinder valve
Flow meter
Safety nut
Drive roll tension adjustment
Wire spool
Cylinder
Wire guide
Volt and/or amp meters
Wire spool Over run adjustment
Gun
Gas hose
Feed rolls
Welding current adjustment
Ground clamp
Welding current taps
Ground Lead
7
GMAW Gun
Welding Wire
Insulation ring
Gas orifice
Liner
Nozzle
Gas diffuser
Contact tube
Trigger
8
Flow meter
  • GMAW systems use a flow meter to provide a
    constant flow rate (ft3/min) of shielding gas.
  • Two types of flow meters are used based on the
    principle that to vary the flow rate of a gas you
    must either change the pressure, or change the
    metering orifice size.
  • One piece the flow is regulated by using a fixed
    orifice and changing the pressure to change the
    flow rate.
  • Two piece the flow is regulated by using a
    constant pressure regulator and changing the flow
    rate with an adjustable orifice (needle valve).
  • The two piece flow meter does a better job of
    maintaining a constant flow rate.

9
Methods of Controlling The Weld
  • Semiautomatic
  • Equipment controls the feeding of the electrode
    to a hand held welding gun.
  • The operator sets the machine, positions the gun,
    starts and stops the process by a trigger on the
    gun, and controls the movement of the gun.
  • Operator must maintain the correct stickout, gun
    alignment with the joint and welding speed.

10
Methods--cont.
  • Automatic
  • Operator positions parts and programs machine.
  • Robotic equipment positions the gun and controls
    movement.

11
Methods--cont.
  • Mechanized
  • Gun is mounted in a carriage or other device that
    positions it in the weld and manipulates it.
  • The operator is responsible for operating the
    controls that start and stop the weld and moving
    the gun along the joint.
  • MIG gun may be stationary and the work moves pass
    beneath it.
  • The machine controls the gun position, stickout
    and welding speed.

12
Summary of Methods
13
GMAW Processes
  • The GMAW process provides four different metal
    transfer methods.
  • Short circuiting
  • Spray
  • Globular
  • Pulse spray

14
Short Circuiting Transfer
  • When the gun trigger is activated, the wire
    starts to move toward the metal.

When the wire touches the metal it shorts out.
The wire touches the metal and the process
continues
The high current flow melts the end of the wire
and a droplet is formed.
As the wire continues to move, the arc restarts.
The current pinches off the droplet and the arc
stops.
  • Process is recognizable by its sharp buzzing or
    crackling sound
  • Most common method

15
Spray Transfer
  • Requires high current. The higher current
    density of the spray process causes the wire to
    melt into small droplets (less than the diameter
    of the wire).
  • The arc forces propels the droplets to the metal.
  • The puddle is larger and more fluid.
  • The high current density results in deeper
    penetration.
  • High current results in high deposition rate.
  • Process results in a hissing or whispering sound.
  • Preferred process for thick metal in the flat
    position.

16
Globular Transfer
  • Low current density results erratic arc and
    globules of metal larger than the diameter of the
    wire.
  • Minimum penetration.
  • Excessive spatter
  • Use is limited to submerged arc welding.

17
Pulse Spray Transfer
  • Process starts as short circuiting, but instead
    of the current peak staying on when the wire is
    shorted, the current is lowered after a period of
    time to a background current.
  • Produces a heating and cooling effect like short
    circuiting.
  • Cooling improves puddle control, spray period
    produces deep penetration.

A Peak Current B Background Current C Peak
Time D Pulses per Second
18
Stickout
  • An important function of all GMAW processes is
    the stickout.
  • Stickout is the distance from the end of the
    contact tube to the weld surface.
  • Insufficient stickout will cause the wire to fuse
    to the contact tube.
  • Excessive stickout will cause the wire to
    overheat and it will melt into irregular pieces.

19
FCAW
20
Introduction
  • FCAW (Flux Core Arc Welding) uses a hollow wire
    that is filled with flux.
  • Same transfer methods as GMAW.
  • Two types
  • Externally shielded
  • Self shielded

21
External Shielded
  • Requires the same gas equipment used in the GMAW
    process.
  • Less cleaning is required when compared with self
    shielded wire.
  • Produces a large volume of fumes
  • Weld must be protected from air currents and
    drafts.
  • Small diameter wires, all positions.
  • The combination of flux core and external
    shielding allows welding engineers to customize
    the shielding environment for specialized metals.

22
Self Shielded
  • Shielding is provided by flux in the core of the
    wire.
  • Produces a large volume of fumes.
  • Can withstand more wind and draft than external
    shielded wire.
  • Will have slag to remove.
  • Does not require the use of a nozzle.
  • Nozzle is usually left on to help maintain
    stickout.

23
GMAW Equipment
24
GMAW Equipment
  • Power source
  • Wire feeder and controls
  • Welding gun and components
  • Shielding gas delivery system
  • Weld cleaning and finishing tools

25
Power Supply
  • GMAW and FCAW both use a constant voltage power
    supply.
  • Many different types are available.
  • Industrial rate are usually 100 duty cycle.
  • Non industrial power supplies have sloping duty
    cycle.
  • May have a built in heat sensitive overload
    switch.
  • Install power supply so that the cooling air
    through the machine is not restricted.

26
Selecting Power Supply
  • Seven factors to consider when selecting a GMAW
    or FCAW power supply.
  • Type of metal
  • Metal thickness range
  • Type of metal transfer
  • Wire diameter range
  • Primary power available
  • Capacity of power source
  • Control and adjustments

27
Wire Feeding systems
  • Function is to deliver the welding wire at a
    constant rate to the gun.
  • Three systems
  • Push
  • Pull
  • Push--pull
  • Two types
  • Constant speed
  • Voltage sensing
  • Two types of construction
  • Internal
  • External

28
Wire Drive Systems
  • The drive system is responsible for pulling the
    wire from the spool and then pushing the wire
    down the cable.
  • The wire drive systems consisted of one or more
    pair of feed rolls and wire guides.
  • The guides must be the proper size and adjusted
    close to the feed rolls and aligned with gap
    between the rolls.

29
Feed Rolls
  • For a GMAW system to work correctly, the feed
    rolls must be the correct type and size.
  • The feed roll tension must also be set correctly.

U Groove
V Groove
Knurled V groove
Cogged U groove
30
Welding Gun
  • Function is to deliver the shielding gas, wire
    and welding current to the weld pool.
  • MIG guns are rated on amperage capacity.
  • The reason is heat.
  • 400 amps are water cooled.
  • Welding wire is delivered to the gun by the
    liner.
  • Liner must sized to the welding wire.
  • Small liner excessive friction which may cause
    the wire to seize.
  • Large liner wire can buckle and spring forward
    causes erratic wire feed.
  • Liner must be correct length.
  • Cable
  • Insulation ring
  • Gas diffuser
  • Contact tube
  • Wire
  • Nozzle

31
Welding Gun--cont.
  • Contact tube
  • Sliding electrical connection.
  • Must match the diameter of the wire
  • Must be replaced frequently
  • The nozzle directs the shielding gas towards the
    weld pool.

Nozzle
Contact tube
32
Consumables
  • Shielding gas
  • Carbon dioxide
  • Requires special valve
  • Must use washer between valve and flow meter.
  • Argon
  • Mixture
  • Welding wire
  • Solid (Copper clad)
  • Flux core
  • Stainless steel
  • Hard surfacing
  • Aluminum

33
Questions
About PowerShow.com