GMAW Fundamentals Gas Metal Arc Welding Metal Inert Gas By: Wanda Sue Benton ESAB University & Florence-Darlington Technical College Introduction  GMAW is defined as arc welding using a continuously fed consumable electrode and a shielding gas.  GMAW is also known as MIG (Metal Inert Gas).  Produces high-quality welds  Yields high productivity Advantages  Large gaps filled or bridged easily  Welding can be done in all positions  No slag removal required  High welding speeds  High weld quality  Less distortion of work piece Types of Metal Transfer The basic GMAW process includes three distinctive process techniques: 1. 2. 3. Short Circuit (Short Arc) Globular Transfer Spray Arc Transfer Short Circuit (Short Arc)  Operates at low voltages and welding current  Small fast-freezing weld puddle obtained  Useful in joining thin materials in any position, as well as thick materials in vertical and overhead positions  Metal transfer occurs when an electrical short circuit is established 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 Spray Arc 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 Manual GMAW Equipment  Three major elements are : 1.) Welding torch and accessories 2.) Welding control & Wire feed motor 3.) Power Source  GMAW equipment can be used either manually or automatically WIRE CONTROL & WIRE FEED MOTOR POWER SOURCE Welding Torch & Accessories  The welding torch guides the wire and shielding gas to the weld zone.  Brings welding power to the wire also  Major components/parts of the torch are the contact tip, shielding gas nozzle, gas diffuser, and the wire conduit GAS DIFFUSER NOZZLE TRIGGER CONTACT TIP INSTALLED COMPONENTS Welding Control & Wire Feed Motor  Welding control & Wire feed motor are combined into one unit  Main function is to pull the wire from the spool and feed it to the arc  Controls wire feed speed and regulates the starting and stopping of wire feed  Wire feed speed controls Amperage WIRE FEEDER Power Source  Almost all GMAW is done with reverse polarity also known as DCEP  Positive (+) lead is connected to the torch  Negative (-) lead is connected to the work piece  Provides a relatively consistent voltage to the arc  Arc Voltage is the voltage between the end of the wire and the work piece POSITIVE TERMINAL NEGATIVE TERMINAL Shielding Gases  Purpose of shielding gas is the protect the weld area from the contaminants in the atmosphere  Gas can be Inert, Reactive, or Mixtures of both  Gas flow rate is between 25-35 CFH  Argon, Helium, and Carbon Dioxide are the main three gases used in GMAW FLOW METER CFH PRESSURE ADJUSTMENT KNOB CYLCINDER PRESSURE GAUGE