Advanced Welding Processes: Technologies and Process Control

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∑ low current: 0.1–15 A; ∑ intermediate current: 15–200 A; ∑ high current: above 200 A. Advanced gas tungsten arc welding 89 Low-current or ‘microplasma’ welding: In the low-current range the principal advantage of the process over GTAW is the excellent arc stability even at levels of 1–2 A at which it would be difficult to operate a GTAW arc. Restricted arc root area and improved directionality are added advantages. At low currents, the pilot arc ensures reliable main arc starting and can also be used to illuminate the joint before welding. These features of the process make it suitable for joining very thin materials, for the encapsulation of electronic components and sensors, the joining of fine-mesh filter elements [98] or repair of turbine blades. Intermediate-current plasma welding. In the range 15–200 A, the process is similar in characteristics to GTAW but, for the same mean current, higher speed or improved melting efficiency may be achieved. In addition, the plasma process is more tolerant to variations in stand-off and the tungsten electrode is protected from accidental touch-down and contamination. The process has been used in this range for the joining of silicon iron transformer laminations where contamination of the electrode presents problems in the GTAW process. High-current plasma operation. At high currents, the keyhole mode of operation may be used. This makes it possible to perform single-pass square butt welds from one side in plate thicknesses up to about 9 mm. Accurate alignment of the torch and stable travel speed are important in this mode to avoid undercut. Typical applications of keyhole plasma welding are highspeed longitudinal welds on strip and pipe. The process has also been used for root runs in thick-wall pipe. 6.3.8 Multicathode GTAW One of the principal factors which limits the maximum welding speed of the GTAW process is the occurrence of undercut [99] (see Section 6.4 below) and although dual-shield and plasma techniques increase the potential heating efficiency of the arc, they also have a tendency to increase the risk of undercut and this, in turn, limits their usefulness for high-speed welding. This problem may be overcome by creating an elongated heat source using two or more arcs in series (Fig. 6.12). This technique is called multicathode GTAW and was originally developed in the 1970’s. [100] The welding speed obtained is determined by the number of electrodes and their separation but, as shown in Fig. 6.13, these are significantly higher than the travel speeds obtained with conventional GTAW. This process variant has been used mainly for specialized applications in the high-speed welding of the longitudinal seams in tube mills. In order to avoid the tendency for the arcs to deflect under the influence
90 Advanced welding processes Gas shield Three electrically isolated electrodes 6.12 Multicathode GTAW. Welding speed (mm min –2 ) 2500 2000 1500 1000 500 a b c Elongated weld pool 0 50 100 150 200 250 Current (A) a c Three cathodes Single electrode b Two cathodes 6.13 Increases in welding speed achieved using multiple electrodes for full-penetration butt welds. (Material used: 1.2 mm 304-type stainless steel.)
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Advanced welding processes i
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Advanced welding processes Technolo
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Contents Preface ix Acknowledgement
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Contents vii 10.4 Automated control
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Welding has traditionally been rega
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Acknowledgements I would like to ac
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1.1 Introduction Welding and joinin
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An introduction to welding processe
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Stage 1 Stage 2 An introduction to
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Slag deposit on weld surface An int
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∑ no heavy slag - reduced post-we
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Electro slag SAW multi wire SAW FCA
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Weld metal used (kg m -1 ) 40 35 30
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Advanced process development trends
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% consumed 70 60 50 40 30 20 10 Adv
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Advanced process development trends
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Mains input Power regulation Contro
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Welding power source technology 29
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Three-phase transformer Three-phase
Page 52 and 53: Mains input Welding power source te
Page 54 and 55: Off line storage Operator interface
Page 56 and 57: Welding power source technology 43
Page 58 and 59: 4.2.1 Improved toughness Filler mat
Page 60 and 61: Filler materials for arc welding 47
Page 62 and 63: Flat strip Solidified slag on weld
Page 72 and 73: Gases for advanced welding processe
Page 76 and 77: CVN impact energy (J) 200 150 100 5
Page 78 and 79: ∑ argon plus 15-25% carbon dioxid
Page 80 and 81: 25 23 21 19 17 15 13 11 9 7 20 18 1
Page 84 and 85: Ozone emission (ml min -1 ) 4 3 2 1
Page 86 and 87: Table 5.3 Continued Argon + 1 to 7%
Page 88 and 89: Advanced gas tungsten arc welding 7
Page 90 and 91: Power source Advanced gas tungsten
Page 92 and 93: Number of arc starts 35 30 25 20 15
Page 98 and 99: Water cooling 6.7 Dual-shielded GTA
Page 110 and 111: Surface tension Surface tension Adv
Page 114 and 115: 7.2.1 Globular drop transfer Metal
Page 116 and 117: Gas metal arc welding 103 projected
Page 118 and 119: Droplet forming 7.6 Drop spray tran
Page 120 and 121: Number of counts 100 80 60 40 20 0
Page 122 and 123: Metal cored Rutile Basic Self-shiel
Page 124 and 125: F d Fem F v F st F g 7.13 Balance o
Page 126 and 127: Gas metal arc welding 113 is the cu
Page 128 and 129: Stick out Dip transfer Pulse/spray
Page 130 and 131: Gas metal arc welding 117 V = M + A
Page 132 and 133: Voltage (V) 50 40 30 20 10 Gas meta
Page 134 and 135: Pulse current t p 7.23 Pulsed trans
Page 136 and 137: Gas metal arc welding 123 The mean
Page 138 and 139: Wire feed rate (m min -1 ) 11 10.5
Page 140 and 141: Gas metal arc welding 127 Improveme
Page 142 and 143: Gas metal arc welding 129 and a num
Page 144 and 145: Current (A) 500 400 300 200 100 0 G
Page 146 and 147: Pulse amplitude (A) 500 400 300 200
Page 148 and 149: Gas metal arc welding 135 otherwise
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High-energy density processes 139 P
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Arc voltage 30 25 20 15 10 High-ene
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High-energy density processes 143 N
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Reflecting mirror Laser cavity Powe
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High-energy density processes 147 H
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Laser beam Gas lens Plasma control
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High-energy density processes 151 P
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High-energy density processes 153 M
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High-energy density processes 155 a
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High-energy density processes 157 l
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High-energy density processes 159 p
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8.4.5 Practical considerations High
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Sliding particle stop Undeflected b
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9.1 Introduction 9 Narrow-gap weldi
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6-16 mm Parallel-sided with backing
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Water cooling Main Shielding-gas po
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Narrow-gap welding techniques 171 T
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9.7 ‘Twist arc’ narrow-gap GMAW
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GMAW torch The NOW process GMAW tor
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Narrow-gap welding techniques 177 T
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10.1 Introduction 10 Monitoring and
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Monitoring and control of welding p
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PROJECT: WELDING CODE : WELDING PRO
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TYPE TOUGHNESS TEST TYPE No. TEMP R
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Data RAM ADC I/O device Monitoring
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Current I(A) 150 140 130 120 110 Mo
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Table 10.5 Stability criteria Monit
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CCD camera Travel direction Torch M
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Welding automation and robotics 219
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Table 11.1 Robot applications Weldi
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∑ evaluate alternatives; ∑ eval
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Option Manual metal arc Gas metal a
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Appendices Appendices 247
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Arc Metal arc Manual metal arc Resi
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Tensile strength Appendices 251 Des
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Appendices 253 Exx16 Basic low-hydr
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GMAW stainless steel c Wire feed sp
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Appendix 4 American, Australian and
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Appendices 259 Carbon Manganese ste
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Consumable type Features Applicatio
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Appendix 7 Plasma keyhole welding o
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References [1] British Standards In
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References 267 [40] Anon, 1989 ‘S
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References 269 [88] Boughton P and
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References 271 Century Conference (
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References 273 [178] Benn B, 1988
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References 275 [224] Philpott M L,
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References 277 [269] UK Patent 8411
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Activated TIG (A-TIG) 91, 97 adapti
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digital measuring systems 189-90 di
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high-frequency high-voltage arc ini
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current measurement 194-6 determina
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carbon dioxide 63-4, 64-6 chlorine
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Advanced Welding Processes: Technologies and Process Control

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