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 times per second

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 Video Globular

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 Video

Introduction – Polarity Almost all GMAW welding is done with Reverse Polarity DC+ or DCEP (Direct current Electrode Positive)

Advantages of GMAW Welding 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 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: - wire feeds - gas flows - welder is energized

Equipment – Torch / Gun 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 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 1.Stop welding. 2.Turn off power source, roll up cords. 3.Turn off shielding gas at the source. 4.Roll up ground cable and gun. 5.Return Welder to original place kept. 6.CLEAN UP AFTER YOURSELF!!!