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Gas Tungsten Arc Welding of Plate

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1 Gas Tungsten Arc Welding of Plate
Chapter 16 Gas Tungsten Arc Welding of Plate

2 Objectives Name the applications for which the gas tungsten arc welding process is more commonly used Discuss the effects on the weld of varying torch angles Explain why the filler rod end must be kept inside the protective zone of the shielding gas and how to accomplish this Tell how tungsten contamination occurs and what should be done when it happens

3 Objectives (cont'd.) Explain what can cause the actual welding amperage to change Determine the correct machine settings for the minimum and maximum welding current for the machine used, the types and sizes of tungsten, and the metal types and thicknesses List factors that affect the gas preflow and postflow times required to protect the tungsten and the weld

4 Objectives (cont'd.) Determine the minimum and maximum gas flow settings for each nozzle size, tungsten size, and amperage setting Compare the characteristics of low carbon and mild steels, stainless steel, and aluminum in respect to GTA welding Describe the metal preparation needed before GTA welding

5 Objectives (cont'd.) Demonstrate how to properly make GTA welds in butt joints, lap joints, and tee joints in all positions that can pass the specified standard

6 Introduction Gas tungsten arc welding Also called GTA welding
Can be used to for nearly all types and thicknesses of metal Fluxless, slagless, and smokeless Welders have fine control of the welding process Used when appearance is important Setup of equipment affects weld quality Charts give correct settings Field conditions affect the variables

7 Torch Angle Key points Torch should be held as close to perpendicular as possible May be angled zero to fifteen degrees from perpendicular for better visibility As the gas flows out it must form a protective zone around the weld Too much tilt distorts protective shielding gas zone Velocity of shielding gas affects protective zone as torch angle changes

8 Filler Rod Manipulation
Filler rod must be kept inside the protective zone If removed from the gas protection Oxidizes rapidly: oxide is added to weld pool Rod tip becomes oxidized: cut it off Weld is temporarily stopped Shielding gas must be kept flowing Rod should enter shielding gas as close to base metal as possible Angles under 15 degrees prevent air from being pulled in welding zone

9 FIGURE 16-2 The hot filler rod end is well within the protective gas envelope.
Larry Jeffus

10 FIGURE 16-5 Filler being remelted as the weld is continued.
Larry Jeffus

11 Tungsten Contamination
Most frequent problem Tungsten becomes contaminated if it touches molten weld pool or filler metal Surface tension pulls contamination up onto the hot tungsten Extreme heat causes some of the metal to vaporize and form a large oxide layer

12 FIGURE 16-8 Contaminated tungsten.
Larry Jeffus

13 Tungsten Contamination (cont'd.)
Contamination forms a weak weld Weld and tungsten must be cleaned before any more welding can be done Tiny tungsten particles will show up if the weld is X-rayed Contamination can be knocked off quickly by flipping the torch head

14 FIGURE 16-8 Contaminated tungsten.
Larry Jeffus

15 Current Setting Amperage on machine's control is the same at the arc when: Power to machine is exactly correct Lead length is very short All cable connections are perfect Arc length is exactly right Remote current control is in full on position

16 Experiments Designed to help new welders learn basic skills Learn more
Help troubleshoot welding problems Learn more Subtle changes will become more noticeable Even experienced welders make changes

17 Figure 16-10 Melting first occurring.
Larry Jeffus

18 Gas Flow Gas preflow and postflow times depend upon:
Wind or draft speed Nozzle size Tungsten size Amperage Joint design Welding position Type of metal welded Maximum flow rates must never be exceeded

19 Practice Welds Grouped according to weld position and type of joint
Mild steel Inexpensive Requires the least amount of cleaning Aluminum Cleanliness is a critical factor Try each weld with each metal Determine which metal will be easier to master

20 Low Carbon and Mild Steels
Two basic steel classifications Most common During manufacturing small pockets of primary carbon dioxide gas become trapped Do not affect strength Porosity: likely when not using a filler metal Most filler metals have some alloys (i.e., deoxidizers) Prevent porosity caused by gases trapped in base metal

21 Stainless Steel Setup and manipulation
Nearly the same as for low carbon and mild steels Welds show effects of contamination Precleaning is important Most common problem Bead color after the weld Using a low arc current with faster travel speeds is important Carbide precipitation

22 Aluminum Molten aluminum weld pool
High surface tension Preheat base metal in thick sections Preheat temperature is around 300 degrees Fahrenheit Cleaning and keeping the metal clean Time consuming Aluminum resists oxidation at room temperature Rapidly oxidizes at welding temperatures

23 FIGURE 16-15 Aluminum filler being correctly added to the molten weld pool.
Larry Jeffus

24 Metal Preparation Base and filler metals Must be thoroughly cleaned
Contamination will be deposited into the weld Oxides, oil, and dirt are the most common Contaminants can be removed mechanically or chemically

25 Summary Position yourself to control the electrode filler metal and to see the joint Experienced welders realize they need to see only the leading edge of the weld pool Good idea to gradually reduce your need for seeing 100% of the weld pool Increasing this skill is significant advantage Welding in the field May have to be done out of position

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