Advanced Welding Processes: Technologies and Process Control

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Advanced gas tungsten arc welding 99 Table 6.4 Principal control parameters for GTAW and plasma processes Control parameters GTAW Current, pulse parameters, current rise/decay times, electrode polarity, welding speed, electrode geometry, shielding gas type, shielding nozzle size, shielding gas flow stabilisation (gas lens), shielding gas flow rate, electrode protrusion Additional control parameters for PLASMA Electrode set back, nozzle geometry, orifice diameter, plasma gas type, plasma gas flow, pilot arc current use of alternative shielding gases, surface active coatings and sophisticated power sources, as well as fundamental variations such as the dual-gas and plasma welding systems. The application of these techniques can offer improved weld quality and increased productivity. A better understanding of the way in which the process control variables influence joint quality has been developed and this has enabled further advances to be made in the automation of the process. Some of the resultant developments will be discussed in Chapter 11.
7.1 Introduction Due to its high operating factor and deposition rate, gas metal arc welding (GMAW) has the potential to improve productivity over that obtained with the GTAW and SMAW processes. Although the requirement to exploit the economic benefits of the process has led to a clear trend towards greater use of GMAW worldwide, it has in the past proved difficult to obtain reliable quality. The main thrust of development has therefore been to improve control and achieve more consistent quality. In order to discuss the advances which have been made in this direction it is necessary to reconsider the process fundamentals, in particular metal transfer in GMAW and control of conventional GMAW. 7.2 Metal transfer in GMAW The way in which material is transferred from the tip of the consumable electrode into the weld pool has a significant influence on the overall performance of GMAW: it affects process stability, spatter generation, weld quality and the positional capabilities of the process. Phenomenological studies of the mode of metal transfer have been carried out using high-speed cine or stroboscopic cine and video techniques. [109] The various natural types of transfer have been classified into groups. A simplified basic classification is shown in Fig. 7.1. In free-flight transfer an arc is maintained between the electrode and the workpiece and the metal is transferred across the arc in the form of droplets. The size of the droplets and frequency of transfer may vary considerably and several subdivisions of free-flight transfer are necessary to accommodate these variations. The common free-flight modes are: ∑ globular (drop and repelled); ∑ spray (drop projected streaming). 100 7 Gas metal arc welding
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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
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Mains input Welding power source te
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Off line storage Operator interface
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4.2.1 Improved toughness Filler mat
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Filler materials for arc welding 47
Page 62 and 63: Flat strip Solidified slag on weld
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Page 72 and 73: Gases for advanced welding processe
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Page 78 and 79: ∑ argon plus 15-25% carbon dioxid
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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%
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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 102 and 103: ∑ low current: 0.1-15 A; ∑ inte
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
Page 150 and 151: High-energy density processes 137
Page 152 and 153: High-energy density processes 139 P
Page 154 and 155: Arc voltage 30 25 20 15 10 High-ene
Page 156 and 157: High-energy density processes 143 N
Page 158 and 159: Reflecting mirror Laser cavity Powe
Page 160 and 161: 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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