Lesson 8

1. Lesson 8 Applying Tungsten Inert Gas (TIG) Welding Techniques

2. Next Generation Science/Common Core Standards Addressed! • Words and phrases as they are used in a specific scientific or technical context relevant to grades 9–10 texts and topics. • CCSS.ELA Literacy.RST.9‐10.3Follow precisely a complex multistep procedure when carrying out experiments, taking measurements, or performing technical tasks, attending to special cases or exceptions defined in the text. CCSS.ELA • CCSS.ELA Literacy. RST.11Follow precisely a complex multistep procedure when carrying out experiments, taking measurements, or performing technical tasks; analyze the specific results based on ex CCSS.ELA Literacy. • RST.11‐12.4 explanations in the text‐12.3 Determine the meaning of symbols, key terms, anCCSS.ELA Literacy.RST.9‐10.3Follow precisely a complex multistep procedure when carrying out experiments, taking measurements, or performing technical tasks, attending to special cases or exceptions defined in the text. • CCSS.ELA Literacy.RST.9‐10.4 Determine the meaning of symbols, key terms, and other domain‐specific words and phrases as they are used in a specific scientific or technical context relevant to grades 9–10 texts and topics. • CCSS.ELA Literacy. RST.11Follow precisely a complex multistep procedure when carrying out experiments, taking measurements, or performing technical tasks; analyze the specific results based on ex CCSS.ELA Literacy. • RST.11‐12.4 explanations in the text‐12.3 Determine the meaning of symbols, key terms, and other domain‐specific words and phrases as they are used in a specific scientific or technical context relevant to grades 11–12 texts and topics. • MP.4 Model with mathematics. (HS‐PS1‐4 • d other domain‐specific words and phrases as they are used in a specific scientific or technical context relevant to grades 11–12 texts and topics. • MP.4 Model with mathematics. (HS‐PS1‐4

3. 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. • 4. Identify the types of shielding gases used for TIG welding.

4. Centerless ground electrode Clean finished electrode Duty cycle Flowmeter Polarity Postweld purge time Terms

5. 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?

6. 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?

7. 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.

8. A. At one time, the American Welding Society called the process “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.

9. B. 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. • Welds are not weakened by slag inclusion in the bead because the flux used is a gas.

10. The TIG Process 2. The TIG welding process is known for its consistency in producing high quality welds. 3. 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.

11. The TIG Process • 4. The finished weld requires little, if any, grinding or preparation before it can be painted. • 5. There is usually less distortion of the workpiece because of the small heat affected zone.

12. The TIG Process • 6. The TIG process has many applications because it can be used to make high quality welds in almost any metals and alloys. • 7. 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.

13. The TIG Process • 8. TIG can be performed by both automatic and manual techniques. • 9. TIG may be done in all positions. • 10. TIG may be used on a wide range of metal thickness.

14. What are the applications for the Tungsten Inert Gas (TIG) process?

15. With the technological developments made in TIG equipment, it is now the most versatile of all the fusion welding processes.

16. 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.

17. 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. Stainless steel is used extensively in the dairy and food processing industries.

18. 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.

19. How does the Tungsten Inert Gas (TIG) process work?

20. In the TIG process, an arc is struck between the non-consumable tungsten electrode and the work piece.

21. A. The thickness of the metal and the type of current being used determine the size of the tungsten electrode. B. The possible currents available are Direct Current Straight Polarity (DCSP), Alternating Current (AC), or Direct Current Reverse Polarity (DCRP).

22. C. 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. • 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.

23. C2. 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. • 3. The torch may be moved in a semicircular motion to vary the width of the bead.

24. D. 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.

25. What are the types of Tungsten Inert Gas (TIG) equipment and accessories and what is their function?

26. The equipment used for TIG is somewhat different from that used in stick welding and much different from that used in MIG welding.

27. TIG Equipment A. A weldor should know that with certain accessories a regular AC, DC, or AC/DC welding machine can be fitted for TIG welding. • 1. 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.

28. TIG Equipment • 2. Direct current flowing from the electrode (–) to the workpiece (+) is direct current straight polarity, or DCSP.

29. TIG Equipment • 3. Current which flows from the workpiece (–) to the electrode (+) is direct current reverse polarity, or DCRP.

30. TIG Equipment • B. Most TIG welding is done with AC or DCSP current. • 1. When welding with AC, the machine will be either balanced or unbalanced. • 2. With AC machines, the current, in theory, flows in DCSP half of the time and DCRP half of the time.

31. TIG Equipment 3. 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. • 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.

32. TIG Equipment • 4. 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.

33. TIG Equipment • 5. When the AC machine does not compensate for the high resistance encountered in the DCRP part of the cycle, the sinewave is unbalanced. • a. 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).

34. TIG Equipment b. 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.

35. TIG Equipment c. 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.

36. TIG Equipment 6. 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. • a. The high frequency unit produces high frequency voltage (several thousand volts) at a frequency of several million cycles per second.

37. TIG Equipment b. The current in the high frequency circuit is only a fraction of an ampere. c. Because of the high voltage and frequency, the current is carried on the surface of the conductor rather than penetrating throughout the conductor. d. 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.

38. TIG Equipment 7. On DC machines using an add-on portable high frequency unit, the high frequency circuit will need to be turned off manually. 8. On AC machines TIG welders with high frequency units are used to stabilize the arc and to ionize gases in the arc zone. • The ionized gases make the arc easier to maintain when the current changes directions.

39. TIG Equipment 9. The torches used on TIG welding outfits are electrical devices and have a duty-cycle rating. 10. The duty-cycle is the maximum current that the torch can safely withstand over a 10 minute period of operation.

40. TIG Equipment 11. 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.

42. TIG Equipment 12. The weldor should make sure all connections and fittings are tight. 13. Small capacity TIG welding torches will usually be air-cooled rather than water-cooled.

43. TIG Equipment 14. 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. 15. The volume of gas required and the width of the bead will determine the size of the nozzle needed. a. The shapes of some nozzles are designed to decrease turbulence of the gas stream.

44. TIG Equipment • b. With some nozzles, the electrode may stick out as much as 1 inch without loss of the shielding gas and turbulence. 16. Nozzles are made from ceramic, metal, plastic, and Pyrex glass materials. a. Ceramic nozzles are used on jobs up to 275 amps. b. Metal nozzles or metal-coated ceramic nozzles are used on jobs where 300 or more amps of current are needed.

45. TIG Equipment c. High-temperature plastic and Pyrex glass are transparent and are used in some special applications. 17. The electrodes used in TIG welding may be pure tungsten, tungsten with 1 or 2 percent thoria, tungsten with 0.15 to 0.40 per cent zirconia, or pure tungsten with a core of 1 to 2 per cent thoria.

46. TIG Nozzles

47. TIG Equipment 17a. Pure tungsten electrodes are the least expensive. However, they have less current-carrying capacity and are easily contaminated. This makes them the least desirable for critical welds. b. To improve the electrical conductivity, add small amounts of thoria or zirconia.

48. TIG Equipment c. Electrodes with 1 or 2 per cent thoria have good current-carrying capacity, maintain their shape longer, have good resistance to contamination, and make the arc easier to strike. d. Electrodes with 1 per cent thoria are good for general purpose welds. Two percent thoriated electrodes are used for critical welds on aircraft, missiles, nuclear reactors, and heat exchangers.

49. TIG Equipment 18. The quality of the tungsten-zirconia electrodes is between pure tungsten electrodes and the tungsten-thoria electrodes. 19. Electrodes may be purchased with a clean finish or a centerless ground finish. a. Clean-finished electrodes have a smooth surface, are free of defects, and are good for most GTAW jobs. b. Centerless ground electrodes have a mirror-like finish and are used on jobs where the highest-quality welds are needed.

50. TIG Equipment 20. When selecting an electrode, consider the following criteria: electrode diameter, amperage, type of current, type of shielding gas, and whether the high frequency wave is balanced or unbalanced. 21. Electrodes must be shaped and sized before being used for TIG welding.