Interest Approach • Notice that these welds have been welded with fuel-gas, arc, MIG, and TIG welding. • Can you tell what welding type was done on each? Compare and contrast each of them. • What are the advantages and disadvantages of each process?
Student Learning Objectives • 1. Explain the advantages and developments of the Tungsten Inert Gas (TIG) welding process. • 2. Describe applications for the Tungsten Inert Gas (TIG) welding process. • 3. Explain how the Tungsten Inert Gas (TIG) welding process works.
Student Learning Objectives • 4. Identify the types of Tungsten Inert Gas (TIG) welding equipment and accessories and relate their function. • 5. Identify the types of shielding gases used for Tungsten Inert Gas (TIG) welding and explain their purposes.
Student Learning Objectives • 6. Explain the procedures used for Tungsten Inert Gas (TIG) welding. • 7. Identify the safety practices that should be observed in TIG welding.
Terms • Centerless ground electrode • Clean finished electrode • Duty cycle • Flowmeter • Polarity • Postweld purge time
What are the advantages of using the Tungsten Inert Gas (TIG) welding process? What advancements have led to the development of the TIG welding process?
The Tungsten Inert Gas (TIG) welding process fuses metals by heating them between a non-consumable tungsten electrode and the base metal, while a continuous envelope of inert gas flows out around the tungsten electrode.
Tungsten Inert Gas Welding • The letters “TIG” were used to designate the process. • 1. Later, the definition was changed to “gas tungsten arc welding” and the letters “GTAW” came into popular use. • 2. Today, both of the letters and names are used.
Advantages of TIG • The TIG process has several advantages that account for its popularity and increased use in the agricultural and welding industries. • 1. Welds made with a gas-shielded arc are more corrosion resistant, more ductile, and stronger because the gas is able to completely exclude atmospheric air from the welding zone.
Advantages of TIG • 2. Welds are not weakened by slag inclusion in the bead because the flux used is a gas.
The TIG Process • The TIG welding process is known for its consistency in producing high quality welds. • The welding process is easier than other methods because the weldor can clearly see the welding zone. • There is a minimal amount of smoke, fumes, and sparks created by the TIG process.
The TIG Process • The finished weld requires little, if any, grinding or preparation before it can be painted. • There is usually less distortion of the workpiece because of the small heat affected zone.
The TIG Process • The TIG process has many applications because it can be used to make high quality welds in almost any metals and alloys. • Welds can be made with the TIG process either by applying filler rod to the puddle or by fusing the base metal without a filler rod.
The TIG Process • TIG can be performed by both automatic and manual techniques. • TIG may be done in all positions. • TIG may be used on a wide range of metal thickness.
With the technological developments made in TIG equipment, it is now the most versatile of all the fusion welding processes.
TIG Application A. The TIG process can be used to join most metals. • It welds aluminum and magnesium and their alloys, alloy steels, carbon steels, stainless steels, copper, nickel and nickel alloys, titanium, tin, silicon, aluminum bronzes, and cast iron.
TIG Application B. The TIG process can be adapted for welding in the horizontal, vertical, and overhead positions as well as the flat position. • 1. It is used extensively in applications where weld quality is critical, such as stainless steel piping systems.
TIG Application 2. One limitation of the TIG welding process is the low deposition rate of the filler and metal. • The TIG process will deposit less filler metal per pass than of the other processes. • Because of the increased time needed to complete welds on thick metal, the • TIG process is used most often on thinner metals.
In the TIG process, an arc is struck between the non-consumable tungsten electrode and the workpiece.
TIG Process • The thickness of the metal and the type of current being used determine the size of the tungsten electrode. • The possible currents available are Direct Current Straight Polarity (DCSP), Alternating Current (AC), or Direct Current Reverse Polarity (DCRP).
TIG Process • The arc is covered by a layer of shielding gas which acts as the flux and keeps the nitrogen and oxygen in the air from coming in contact with the molten puddle.
TIG Process • When the puddle is formed on the base metal, the torch is moved along the joint until the workpiece is fused together. • 1. A filler rod may or may not be used.
TIG Process • If a filler rod is used, it should be the same composition as the base metal. • The filler rod is fed manually into the leading edge of the puddle. • The torch may be moved in a semicircular motion to vary the width of the bead.
The movement of the TIG torch and applying filler rod is similar to the movement used in braze welding with an oxy-fuel gas torch.
What are the types of Tungsten Inert Gas (TIG) equipment and accessories and what is their function?
The equipment used for TIG is somewhat different from that used in stick welding and much different from that used in MIG welding.
TIG Equipment • A weldor should know that with certain accessories a regular AC, DC, or AC/DC welding machine can be fitted for TIG welding.
TIG Equipment • The heat energy put into the metal being welded is dependent upon the amperage, arc voltage, and polarity of the arc. • The term polarity is used in describing DC welding circuits and refers to the direction of current flow.
TIG Equipment • Direct current flowing from the electrode (–) to the workpiece (+) is direct current straight polarity, or DCSP.
TIG Equipment • Current which flows from the workpiece (–) to the electrode (+) is direct current reverse polarity, or DCRP.
TIG Equipment • Most TIG welding is done with AC or DCSP current. • When welding with AC, the machine will be either balanced or unbalanced. • With AC machines, the current, in theory, flows in DCSP half of the time and DCRP half of the time.
TIG Equipment • When the current flows in the DCRP half of the cycle, the current is flowing from the workpiece to the electrode, causing a high resistance to current flow.
TIG Equipment • This resistance makes the tungsten electrode heat up. • The resistance occurs because the current is flowing from a large conductor, the base metal, to a concentrated point in the tungsten electrode.
TIG Equipment • When in the DCSP half of the cycle, the current is flowing from the electrode tip, a small conductor, to the workpiece, a large conductor. • This direction of current flow has a cooling effect on the tungsten and enhances its current-carrying capacity.
TIG Equipment • When the AC machine does not compensate for the high resistance encountered in the DCRP part of the cycle, the sinewave is unbalanced. • One-half of the time the voltage is higher than expected (DCSP), and one-half of the time the voltage is lower than expected (DCRP).
TIG Equipment • If the AC machine does not have the circuitry to balance the sinewave, do not set the amperage for more than 50 percent of its rated capacity, or machine damage may result.
TIG Equipment • AC machines designed specifically for TIG welding will have a balanced sinewave. • These welders have a special circuit that compensates for the DCRP part of the cycle, and the voltages in both halves of the sinewave are equal.
TIG Equipment • Whether AC or DC is used for TIG welding, a high frequency (HF) unit must be built into the machine, or a portable one must be attached to it. • The high frequency unit produces high frequency voltage (several thousand volts) at a frequency of several million cycles per second.
TIG Equipment • The current in the high frequency circuit is only a fraction of an ampere. • Because of the high voltage and frequency, the current is carried on the surface of the conductor rather than penetrating throughout the conductor.
TIG Equipment • When TIG welding with DC current, the high frequency unit must be on in order to start the arc. • Once the arc is stabilized, the high frequency unit is turned off.
TIG Equipment • On DC machines using an add-on portable high frequency unit, the high frequency circuit will need to be turned off manually. • On AC machines TIG welders with high frequency units are used to stabilize the arc and to ionize gases in the arc zone.
TIG Equipment • The ionized gases make the arc easier to maintain when the current changes directions.
TIG Equipment • The torches used on TIG welding outfits are electrical devices and have a duty-cycle rating. • The duty-cycle is the maximum current that the torch can safely withstand over a 10 minute period of operation.
TIG Equipment • TIG welding torches contain electrical leads from the welding machine, water- coolant hoses, shielding gas hose, the collet, which holds the tungsten electrode, the electrode cap, and gas nozzle.
TIG Equipment • The weldor should make sure all connections and fittings are tight. • Small capacity TIG welding torches will usually be air-cooled rather than water-cooled.
TIG Equipment • The purpose of the gas nozzles on TIG welding torches is to direct the flow of shielding gas over the welding zone and to decrease turbulence of the shielding gas stream.