Advanced Welding Processes: Technologies and Process Control

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Welding power source technology 31 characteristics by the user simplifies the operation of the equipment and offers adequate control for many applications. It does, however, restrict the possibility of significant improvements in process performance. 3.4 Electronic power regulation systems The availability of high-power semiconductors has led to the development of a range of alternative, electronic power source designs [27] which may be classified as follows: ∑ SCR phase control; ∑ transistor series regulator; ∑ secondary switched transistor power supplies; ∑ primary rectifier–inverter; ∑ hybrid designs. 3.4.1 SCR phase control Silicon-controlled rectifiers (SCRs) may be regarded as ‘switchable’ diodes. The device only starts to conduct in the forward direction when a signal is applied to the gate connection. Under normal circumstances the device cannot be turned off until the forward current falls to zero. These devices may be used instead of the normal diodes in the secondary circuit of a DC power supply. To regulate voltage output, the delay between the normal onset of conduction and the gate signal is varied (Fig. 3.6). If the amplitude of the voltage waveform is fixed, it is necessary to use a long firing delay to achieve low output levels and the ripple in the output waveform becomes severe. This problem may be reduced by using a three-phase SCR bridge, by using a large output inductance, or by using an inter-phase inductance. Alternatively, the SCR control may be placed in the primary of the transformer, in which case some smoothing is obtained from the transformer itself. The use of inductance in any of the forms described above is an effective means of smoothing, but it does limit the dynamic response of the power source. An AC output may be obtained by using SCRs connected ‘back to back’, one set conducting in the positive half-cycle whilst another set conducts in the negative half-cycle. In addition, by using an inductor or an inverter circuit (Fig. 3.7), it is possible to produce a ‘square’ output waveform which offers process benefits in GTAW, MMA and SAW. The advantages of this type of control are its simplicity, robustness and the large amplification obtained that enables high output levels to be controlled by very low-level electronic signals. The speed of response of the system is limited by the necessity to cross current zero before a revised firing angle becomes effective; hence, the best response expected would be in the range of 3 to 10 ms.
32 Mains input Advanced welding processes 3.6 SCR phase control circuit (three-phase) and controlled wave form for a single phase, a-f in the upper diagram are SCRs. The lower traces show the waveform from a single SCR: (i) small firing delay with high mean output; (ii) large firing delay with low mean output. DC input Main transformer Free-wheel diode a b c d e f Inductor Smoothing inductor (i) Current (ii) Current t Time Time t SCR 1 SCR 3 AC output to arc SCR 2 3.7 Simple secondary inverter for ac welding. SCR 4 Electronic control and firing circuit Even with the limitations of ripple and response rate, it is possible to produce power sources with significantly better performance than previous conventional designs and, in particular, it is possible to stabilize the output of the power source by means of feedback control. The SCR phase control a b c d ef Electronic regulator and firing circuit Shunt Current feedback Voltage feedback 1 2 3 4
Page 2 and 3: Advanced welding processes i
Page 4 and 5: Advanced welding processes Technolo
Page 6 and 7: Contents Preface ix Acknowledgement
Page 8 and 9: Contents vii 10.4 Automated control
Page 10 and 11: Welding has traditionally been rega
Page 12 and 13: Acknowledgements I would like to ac
Page 14 and 15: 1.1 Introduction Welding and joinin
Page 16 and 17: An introduction to welding processe
Page 22 and 23: Stage 1 Stage 2 An introduction to
Page 24 and 25: Slag deposit on weld surface An int
Page 26 and 27: ∑ no heavy slag - reduced post-we
Page 30 and 31: Electro slag SAW multi wire SAW FCA
Page 32 and 33: Weld metal used (kg m -1 ) 40 35 30
Page 34 and 35: Advanced process development trends
Page 36 and 37: % consumed 70 60 50 40 30 20 10 Adv
Page 38 and 39: Advanced process development trends
Page 40 and 41: Mains input Power regulation Contro
Page 42 and 43: Welding power source technology 29
Page 50 and 51: 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 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
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Advanced gas tungsten arc welding 8
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Water cooling 6.7 Dual-shielded GTA
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∑ low current: 0.1-15 A; ∑ inte
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Surface tension Surface tension Adv
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7.2.1 Globular drop transfer Metal
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Gas metal arc welding 103 projected
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Droplet forming 7.6 Drop spray tran
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Number of counts 100 80 60 40 20 0
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Metal cored Rutile Basic Self-shiel
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F d Fem F v F st F g 7.13 Balance o
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Gas metal arc welding 113 is the cu
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Stick out Dip transfer Pulse/spray
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Gas metal arc welding 117 V = M + A
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Voltage (V) 50 40 30 20 10 Gas meta
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Pulse current t p 7.23 Pulsed trans
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Gas metal arc welding 123 The mean
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Wire feed rate (m min -1 ) 11 10.5
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Gas metal arc welding 127 Improveme
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Gas metal arc welding 129 and a num
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Current (A) 500 400 300 200 100 0 G
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Pulse amplitude (A) 500 400 300 200
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Gas metal arc welding 135 otherwise
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High-energy density processes 137
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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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