1 / 78

Gas Tungsten Arc Welding

Gas Tungsten Arc Welding. Objectives. Describe the gas tungsten arc welding process List other terms used to describe it What makes tungsten a good electrode Eliminate tungsten erosion Shape and clean a tungsten electrode Grind a point on a tungsten electrode. Objectives (continued).

Download Presentation

Gas Tungsten Arc Welding

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Gas Tungsten Arc Welding

  2. Objectives • Describe the gas tungsten arc welding process • List other terms used to describe it • What makes tungsten a good electrode • Eliminate tungsten erosion • Shape and clean a tungsten electrode • Grind a point on a tungsten electrode

  3. Objectives (continued) • Remove a contaminated tungsten end • Melt the end of the tungsten electrode into the desired shape • Compare water-cooled GTA welding torches to air-cooled torches • The purpose of the three hoses connecting a water-cooled torch to the welding machine

  4. Objectives (continued) • Choose an appropriate nozzle • How to get an accurate reading on a flowmeter • Compare the three types of welding current used for GTA welding • Shielding gases used in the GTA welding process

  5. Objectives (continued) • Define preflow and postflow • Problems resulting from an incorrect gas flow rate • Properly set up a GTA welder • Establish a GTA welding arc

  6. Introduction • The Gas Tungsten Arc Welding (GTAW) process is sometimes referred to as a TIG or Heliarc • TIG is short for tungsten inert gas • An arc is established between a non-consumable tungsten electrode (heating element) and the base metal • The inert gas provides the needed arc characteristics and protects the molten weld pool • When Argon became plentiful, the GTA process became more common

  7. Power Source Basics

  8. Tungsten Electrodes

  9. Tungsten • Tungsten has the following properties: • High tensile strength • Hardness • High melting temperature • High boiling temperature • Good electrical conductivity

  10. Tungsten (continued) • Tungsten is the best choice for a non consumable electrode • High melting temperature • Good electrical conductivity • As the tungsten electrode becomes hot the arc between the electrode and the work stabilizes • But a clean and correctly ground tungsten is needed • Because of the intense heat some erosion of the electrode will occur

  11. Figure 15-1 Some tungsten will erode and be transferred across the arc.

  12. Tungsten (continued) • Ways to limit erosion: • Good mechanical and electrical contact • Use as low a current as possible • Use a water-cooled torch • Use as large a tungsten electrode as possible • Use DCEN current • Use as short an electrode extension as possible • Use the proper shape electrode • Use an alloyed tungsten electrode

  13. Torch Build Out

  14. Torch Build Out

  15. Tungsten (continued) • The collet is the cone-shaped sleeve that holds the electrode in the torch • Large-diameter electrodes conduct more current • The current-carrying capacity at DCEN is about ten times greater than at DCEP • The preferred electrode shape impacts the temperature and erosion of the tungsten • With alternating current, the tip is subjected to more heat than with DCEN

  16. Figure 15-3 The smooth surface of a centerless ground tungsten electrode. Courtesy of Larry Jeffus.

  17. Types of Tungsten Electrodes • Pure tungsten is an excellent nonconsumable electrode • Pure tungsten can be improved by adding: • Cerium • Lanthanum • Thorium • Zirconium

  18. Tungsten Electrodes

  19. Table 15-1 Tungsten Electrode Types and Identification.

  20. Shaping the Tungsten • To obtain the desired end shape: • Grinding (for MS and SS) • Breaking (not recommended due to cost) • Re melting the end (Aluminium welding) • Using chemical compound (doesn’t work that well)

  21. Grinding • Often used to clean a contaminated tungsten or to point the end • Should have a fine, hard stone • A coarse grinding stone with result in more tungsten breakage • Should be used for grinding tungsten only • Metal particles will quickly break free when the arc is started, causing contamination

  22. Figure 15-8 Correct way of holding a tungsten when grinding. Courtesy of Larry Jeffus.

  23. Breaking and Remelting • Tungsten is hard but brittle • If struck sharply, it will break without bending • Try not to do this because of $$$$$$$$ • Holding against a sharp corner and hitting results in a square break • After breaking squarely, melt back the end

  24. Chemical Cleaning and Pointing • Tungsten can be cleaned and pointed using one of several compounds • Heated by shorting it against the work • Dipped in the compound • When the tungsten is removed, cooled, and cleaned, the end will be tapered to a fine point • The chemical compound will dissolve the tungsten, allowing the contamination to fall free

  25. Pointing and Remelting • Tapered tungsten with a balled end is made by first grinding or chemically pointing • The ball should be made large enough so that the color of the end stays dull red and bright red • Increase ball size by applying more current • Surface tension pulls the molten tungsten up onto the tapered end

  26. Figure 15-14 Melting the tungsten end shape.

  27. GTAW Equipment

  28. GTA Welding Equipment“Cadillac Stick Welder” • GTA welding torches are water- or air-cooled • Water-cooled GTA welding torch is more efficient • Water-cooled torch has three hosesconnecting it to the welding machine • Nozzle directs the shielding gas directly on the welding zone • Flowmeterregulates the rate of gas flow

  29. Figure 15-21 Schematic of a GTA welding setup with a water-cooled torch.

  30. Types of Welding Current • DCEN concentrates about 2/3 of its welding heat on the work • Max penetration • High Freq. – start only • DCEP concentrates about 1/3 of its welding heat on the work • Max cleaning action • 2/3 of heat at tungsten – primarily used for balling tungsten for aluminium welding • High Freq. – start only

  31. Types of Welding Current • AC concentrates its heat at 50/50 • Sign wave provides for DCRP (cleaning action) and DCSP (penetration action) • Square wave technology allows for adjusting the cleaning or penetration cycle. • High Freq. is on Continuous so there is equal firing of both sides of sign wave. • DC Component will take place if there is no High Freq.

  32. Figure 15-29 Electrons collect under the oxide layer during the DCEP portion of the cycle.

  33. Figure 15-30 Sine wave of alternating current at 60 cycle.

  34. Shielding Gas

  35. Shielding Gases • Shielding gases used for GTA welding process: • Argon (Ar) • Helium (He) • Or a mixture of two or more gases

  36. Shielding Gases (continued) • Argon effectively shields welds in deep grooves in flat positions • Helium offers the advantage of deeper penetration

  37. Shielding Gases (continued) • Hot start allows a surge of welding current • Preflow is the time gas flows to clear out air in the nozzle • Some machines do not have preflow • Postflow is the time the gas continues flowing after the welding current has stopped

  38. Shielding Gases (continued) • Ionization Potential • Amount of voltage needed to “kick start” the arc • The ionization potential, or ionization energy, of a gas atom is the energy required to strip it of an electron. That is why a shielding gas such as helium, with only 2 electrons in its outer shell, requires more energy (higher voltage parameters) for welding. The ionization potential of a shielding gas also establishes how easily an arc will initiate and stabilize. A low ionization potential means the arc will start relatively easy and stabilize quite well. A high ionization potential has difficulty initiating and may have difficulty keeping the arc stable. • Argon • 15.7 electron volts • Helium • 24.4 electron volts • More penetration

  39. Figure 15-35 Too steep an angle between the torch and work may draw in air.

  40. Remote ControlsFoot or Finger

  41. Remote Controls • Can be used to: • Start the weld • Increase the current • Decrease the current • Stop the weld • Remote can be foot-operated or hand-operated device

  42. Welding Techniques

  43. Objectives • Applications using the gas tungsten arc welding process • Effects on the weld of varying torch angles • Why and how the filler rod is kept inside the protective zone of the shielding gas • How tungsten contamination occurs and what to do • Causes of change in welding amperage • Correct settings for the minimum and maximum welding current

  44. Objectives (continued) • Types and sizes of tungsten and metal • Factors affecting gas preflow and postflow times • Minimum and maximum gas flow settings: • Nozzle size • Tungsten size • Amperage setting • Characteristics of low carbon and mild steels, stainless steel, and aluminum • Metal preparation for GTA welding • Make GTA welds in all positions

  45. Introduction • Gas tungsten arc is also called GTA welding • GTA welding can be used to for nearly all types and thicknesses of metal • GTA welding is fluxless, slagless, and smokeless • Welders have fine control of the welding process • GTA welding is ideal for close-tolerance welds • Some GTA welds make the critical root pass • GTA used when appearance is important

  46. Introduction (continued) • Setup of GTA equipment affects weld quality • Charts give correct settings • Field conditions affect the variables in the charts • Experiments designed to evaluate the appearance of a weld • After welding in the lab, troubleshooting field welding problems is easier • To make a weld is good: to solve a welding problem is better

  47. Torch Angle • As close to perpendicular as possible • May be angled 0-15 degrees from perpendicular for better visibility • As the gas flows out it forms a protective zone around the weld • Too much tilt distorts protective shielding gas zone

  48. Figure 16-5 Filler being remelted as the weld is continued. Courtesy of Larry Jeffus.

More Related