GAS TUNGSTEN ARC WELDING GTAW OBJECTIVES Upon completion

GAS TUNGSTEN ARC WELDING GTAW

OBJECTIVES • Upon completion of this unit students will be able to: • • • Describe the GTAW process, Identify GTAW equipment, Select the appropriate tungsten, Understand the PPE requirements for GTAW, Demonstrate proper cleaning, Demonstrate control of welding variables to produce a good weld, and • Demonstrate GTAW welding on various base metals.

INTRODUCTION • GTAW was developed in the 1930 s to weld magnesium for the aircraft industry. • In 1941 the process evolved for use on steel and stainless with the use of helium. • Later on other improvements allowed for the modern welding process that we know today. • GTAW allows a welder to weld on all metals unlike other welding processes. • GTAW also produces some of the most high quality welds. • It is significantly more complex and slower.

GTAW EQUIPMENT • Equipment for GTAW includes the following: • Power Source • Welding Torch • Gas Cylinders • Consumables for GTAW includes the following: • Filler Metals • Shielding Gas • Electrodes

GTAW POWER SOURCES • The same type of power supply used for SMAW is used for GTAW • Constant current machines • GTAW specifically designed machines have more controls on them for adjusting: • • • Polarity Amperage Shielding Gas High Frequency Pulse

GTAW POWER SOURCES CONT. • DCEN is used for most every metal except Aluminum. • AC High Frequency Current is used on Aluminum and Magnesium. • It produces a cleaning action to remove oxides that form immediately when exposed to the atmoshphere

UNIQUE FEATURES OF GTAW EQUIPMENT • High Frequency Start • Creates an arc that can jump long distances to prevent tungsten contamination. • Remote controls • Foot pedal • Thumb wheel • Lift Arc • Allows the tungsten to touch the parent material and be lifted to initiate the arc.

GTAW WELDING TORCH • The GTAW welding torch is very similar to the GMAW welding torch except the tungsten replaces the continuously feed electrode. • Most GTAW torch parts are interchangeable making them suitable for a variety of welding applications. • Torches come it two basic setups water cooled and air cooled. • Torches can be rated from 200 amps to 600 amps. • Torches can hold tungsten's from 1/16’’ up to 5/32’’

PARTS OF THE TORCH • Parts of the torch include: • • • Torch body End Cap Tungsten Collet body or Gas Lens Collet Nozzle/ Cup

GAS CYLINDERS • Pure Argon is primarily used for GTAW. • However, Helium can be added or be used independently of Argon. • Pure Argon should be set from 2030 CFH • Pure Helium should be set to 60 CFH or more. • Because of the volume of gas used and the expense of the gases a flow meter should be used

FILLER METALS • The most common filler metal is ER 70 s-6. It is used for mild steel. • Filler metals need to match the parent material to produce a weld. • In limited instances Helibrazing can join two similar dissimilar metals. • For example 308 stainless should be welded with 308 filler. • Aluminum is welded with 4043 or 5356. • RG or Gas welding rods cannot be used for GTAW.

TUNGSTEN ELECTRODES • Tungsten electrodes are often termed non-consumable because they are not intended on being consumed. • The two most common sizes used are 3/32 and 1/8 • There are several types of tungsten's all with unique properties.

TUNGSTEN ELECTRODES CONT. • Pure • Have a green band used for welding Aluminum and Magnesium. They have good arc stability when using a balanced AC current. • 2% Thoriated • Are used for welding ferrous metals and have high current capacity. They have a red band. • Ceriated • Have an orange band. They are used on thin metals DC only and for small delicate parts.

TUNGSTEN ELECTRODES CONT. • Lanthanated • Have a gold band. Have excellent arc starting, weld on both AC and DC currents. • E 3 • Have a purple band. These are a cross between a Lanthanated and Zirconiated tungsten. A 1/8 tungsten can be used up to 400 amps. • There are many tungstens for unique applications as well.

GTAW SAFETY AND PPE • When grinding tungstens it is very important not to breath the dust. • Hand washing is also required when grinding Thoriated Tungsten. • This is required since they are mildly radioactive. • Standard Welding PPE is required. • • • Z 87. 1 Safety Glasses Welding hood shade 10 Gantlet style gloves Long Sleeve Cotton Shirt Jeans Leather Boots

GTAW SAFETY AND PPE CONT. • When using High Frequency Arcs it is important that no body is around that uses a pace maker. It can stop their heart. • A respirator is required when welding on metals that contain Chrome. • Darker welding lens may be required welding at higher amperages.

BASE METAL PREP • All parent metal should be cleaned of any oils using acetone. • Mill scale and heavy oxides should be removed. • The filler wire should be cleaned with scotch bright and wiped with acetone. • The area in which the work piece is grounded should also be clean.

GRINDING THE TUNGSTEN • For DC welding a tapered point should be ground that is twice the length of the diameter of the tungsten. • For AC welding a ball should be made. • A ball is made by switching the machine to DCEP and striking an arc on a piece of copper.