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Needham [ref. 36] stated that in order to maintain stability in dip transfer the ratio between the arcing time and the short-circuiting time (so called "M ratio") must be kept within a specific range as constant as possible. Mitta et al. [ref. 37] developed an objective method for assessing process stability by correlating statistical features obtained from the current and voltage waveforms with the results from a subjective assessment of process stability performed by a skilful welder. The authors [ref. 37] found that no single feature correlates well with process stability at all current levels. Therefore, they used multiple regression analysis to obtain an empirical model that relates the normalised standard deviation of short-circuiting time, arcing time, average short-circuiting current and average arcing current to the welder's subjective assessment of process stability. Dilthey et al. [ref. 38] also used a similar method to obtain rules for assessing stability. They have proposed models, based on standard deviation to mean value ratios, for assessing both short term and long term stability in short-circuiting, pulse and spray GMAW. A different approach was adopted by Shinoda and Nishikawa [ref. 39] for the stability assessment of dip transfer welding. They suggested that the use of current- voltage (I-V) line diagrams, instead of the commonly adopted time dependent voltage and current waveforms, would provide information on the effect of both variables as well as of their interaction on the process stability. The proposed method consisted of measuring the area in the I-V diagram corresponding to each short-circuiting cycle and calculating the standard deviation of these areas over a specified number of cycles. The authors [ref. 39] claim that the method was successfully used for assessing the stability characteristics of different wire compositions [ref. 40]. In contrast to the established practice of using descriptive statistical measures some authors are using ratios developed from the features of the welding current and voltage transient waveforms for stability assessment [refs. 41,42,43,44,45,46,47, 48,49,50]. Dyurgerov [ref. 41] found that stable metal transfer and optimum stability are attained at a certain ratio between the short circuit and the mean welding currents. This ratio was also used by Lebedev et al. [ref. 42] to. assess power source dynamics. Lipei et al. [ref. 43] and Jennings [ref. 45] found that the ratio relates qualitatively to the amount of spatter generated. Lipei et al. [ref. 43] state that the ratio should be between 1.5 and 2, in order to keep the weld pool stable and prevent spatter while Lebedev and Sidoreiko [ref. 44] found that the ideal value for the ratio is 1.75 but this can be up to 1.95. Jennings [ref. 45] set the maximum value for the ratio at 2.35, while Lebedev [ref. 46] set its minimum value at 1.35. Lebedev [ref. 46] also uses the ratio of the minimum to mean current to select welding parameters for dip transfer; the minimum permissible value for this ratio is 0.29, below which poor metal transfer and are instability were reported to occur. Vorouin and Goloshcapov [ref. 47] used the ratio of the short circuit time to the droplet transfer cycle time (called the time ratio) to assess process stability in dip transfer; the optimum welding condition was reported to be achieved for ratio values between 0.2 and 0.25. Popkov et al. [ref. 48] found dip transfer conditions to be optimum if the ratio of arcing time to cycle time is between 0.6 and 0.8. Needham [ref. 49] used the ratio of arcing time to short circuiting time (called the M ratio) to 11
establish the stable conditions for dip welding. Gupta et al. [ref. 50] found the ideal value of M ratio to be between 2 and 3. The use of indices formed from the the welding current and voltage waveforms for process assessment was further extended by Ogunbiyi [ref. 51]. This author observed that, when moving from dip to globular and spray transfer, the variation range on the welding current and voltage waveforms reduces, or, in other words, the minimum and maximum current and voltage approach the respective welding average values. Based on this fact, three ratios, so called Transfer Stability Index (TSI)8, Transfer Index (TI)9, and Dip Consistency Index (DCI), were proposed as a means of classifying the mode of metal transfer and its stability. The first two ratios were based on features extracted from the current waveform and would give indication about mode of metal transfer and stability respectively. DCI was based on the voltage waveform and was used to predict and confirm the mode of metal transfer. Equations (2.3), (2.4) and (2.5) define the indices: 77= 'mean I -I mean min TSI = 'mix (2.4) 1.. Vmear - DCI = Vbk (2.5) V. I. where IHR is the arithmetic average of the welding current transient samples acquired in a fixed time period; is the minimum value in the welding current transient samples; I,,,, is the maximum value in the welding current transient samples; mea is the arithmetic average of the welding voltage transient samples acquired in a fixed time period; Vbk is the arithmetic average of all the voltage transient samples less than or equal to V. ". The indices were combined to form monitoring rules, which were successfully applied for assessing mode of metal transfer and stability when welding with different power sources and wire and gas combinations [refs. 35,51]. In a further analysis, Ogunbiyi [ref. 51] observed that the arc power oscillates during metal transfer and that the degree of the fluctuation would depend on the mode of metal transfer. As a result, a new ratio was defined and used for a quick assessment of mode of metal transfer and process stability. This ratio was called Power Ratio (PR): 8 TSI was initially proposed by Dyurgerov [ref. 41] 9 TI was initially developed by Lebedev [ref. 46] 12 (2.3)
Page 1 and 2: CRANFIELD UNIVERSITY GC CARVALHO AN
Page 3 and 4: ABSTRACT The aim of this work was t
Page 5 and 6: I dedicate this work to the memory
Page 7 and 8: FIGURES TABLES APPENDICES NOTATION
Page 9 and 10: 3.3.2.1 Welding parameters generato
Page 11 and 12: References Further reading Appendic
Page 13 and 14: Figure 3.12 Offsets for weld start
Page 15 and 16: Figure 6.31 Voltage step input test
Page 17 and 18: Figure J. 2 Plot of stand-off varia
Page 19 and 20: Table A. 1 Welding extended entity
Page 22 and 23: NOTATION A, Electrode sectional are
Page 24 and 25: Pr(ign) Possibility measure of proc
Page 26 and 27: 1. Introduction Welding is the thir
Page 28: Chapter 4 describes the on-line pos
Page 31 and 32: In pulse transfer, the welding curr
Page 33 and 34: Pd = Pv - pzh-s (2.1) where Pd is t
Page 35: the bridge. Another factor that ind
Page 39 and 40: Philpott [ref. 21] developed an on-
Page 41 and 42: current peak at the moment the tip
Page 43 and 44: obot on the line must be individual
Page 45 and 46: collision detection capabilities wh
Page 47 and 48: cause dynamic variation in the seam
Page 49 and 50: Another type of robot static calibr
Page 51 and 52: spatter the gas nozzle is particula
Page 53 and 54: Table 2.1: Joint positioning tolera
Page 55 and 56: In order to minimise the undesirabl
Page 57 and 58: c) Ultrasonic sensors; d) Through-t
Page 59 and 60: where K,, K2, K3 and K4 are constan
Page 61 and 62: Philpott [refs. 21,131], based on t
Page 63 and 64: centre. This is attributed to the m
Page 65 and 66: technique must be employed to preve
Page 67 and 68: " digital hardware, which is basica
Page 69 and 70: " Maximum value, W.: Wmý = max(W )
Page 71 and 72: process studied over a small range.
Page 73 and 74: In-process welding control is a muc
Page 75 and 76: volume caused by the presence of a
Page 77 and 78: SHIELDING GAS IN CONSUMABLE ELECTRO
Page 79 and 80: Arc voltage Anode Arc length I Anod
Page 81 and 82: computed ideal procedure optimisnti
Page 83 and 84: CONSTANT CURRENT POWER SOURCE `j' O
Page 85 and 86: Original Surface New Surface Electr
Page 87 and 88:
otating welding wire direction weld
Page 89 and 90:
3.1.1.1 Robot errors A robot arm is
Page 91 and 92:
3.2.2 Programming error correction
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3.3.2 Off-line programming module I
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Pen is the weld penetration (side p
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a. 2) Geometrical constraints from
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Step 11 Step 12 Step 13 Step 14 Ste
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Step 21 Step 22 If the wire feed sp
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the Y'-axis results in a positive "
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_ p1e0a - pORoba m31 Ilp! - poll (3
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of a robot in its zero position12 w
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frame points to the front of the ro
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CAD Off-line (AutoCAD) programming
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Z Surface 4 A Y 7 M2 Open Edge Join
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WCF World Co-ordinates Frame 2a = J
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x Torch Co-ordinates Frame o Indica
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vo Ö 't7 Y7 't O m O 'S O O S O S
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ýý aý 0 oA aW ö A O Zt A OO 't
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Ti 9ý-! i4 *Tx t ap31 jx ý- ymin
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errors', (i. e. joint positioning,
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was considered to be outside the sc
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Table 4.3 - Linguistic representati
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The introduction of such a reduced
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Table 4.8 - Final welding process c
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the collection of welding data corr
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Step 4- Calculate the confidence of
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Z Table Co-ordinates Frame Y X Robo
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5.3 Monitoring system The monitorin
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the torch end. Only one degree of f
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Current: 500 Position: 234.5 5.7.3
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I" va JI ºr ö C 3 r" r" rl f_ £-
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IgurC a. H -I UI qur vCiSUJ JpCCU C
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126
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Table 6.1 - Welding trials carried
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Table 6.3 - Coefficients of Ogunbiy
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Note that the calibration model sho
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Table 6.6 - Welding parameters used
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constant set-up welding parameters
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stickout lengths and the temperatur
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of the dip mode of metal transfer.
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which would become active by settin
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In section 4.2.5 it has been mentio
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300 280 260 240 rd 35- 3D 25 20 15
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Figure 6.5 - Measured "versus" Pred
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i S 0 -0.1 -0.2 -0.3 -0.7- 68 10 12
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32.0 E 31.5 y 31.0 30.5 30.0 j 29.5
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35 - 30 p 15 10 0.00 2.60 5.42 8.23
Page 181 and 182:
40 35 30 25 20 15 10 A+iIII+F0.17 2
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30 28 26 24 22 SO_act [mm] DipR [mo
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22 20 18 SO_act [mm] DipR [ohm/100]
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!: 30 25 20t 10 5-- 0 Dip Transfer
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0.430- - 0.380- - :r 0.330 fPR L- 0
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7.2 Tests with varying stand-off an
Page 193 and 194:
Table 7.3 - Bead geometry along the
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ö a2 ., u" u,.., g .,. aucyuaac VI
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0 24-- 22-- 18 210 1 90 0 v 170 mm
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Q 34 32 3o mIm Viewing direction Fl
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ýa 34 mm JO a .. ý nn ýr "u 00 M
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22 20 18 Viewing direction Flange W
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36 33 31 o 29 t 350 310 o 290 U due
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I C, x -i 23 21 j 19 Q 240c WFS =10
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en 34 32 - vsec 30- 26- 24 + .. ++
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186
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" to design and build the hardware
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Although only linear joints were im
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for predicting possibility of bad a
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8.4 Process monitoring and control
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satisfy the required quality criter
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198
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types of joints and multi-pass weld
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[14] NEMCHINSKY, V. A. The effect o
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[38] D1LTHEY, U. , REICHELL, T. , S
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[64] KING, F-J. and HIRSCH, P. Seam
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[86] CARGNELLI, M. and ROGOWSKI, A.
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[109] KURKIN, N. S. and DRIKKER, V.
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[130] USHIO, M. , LIU, W. , MAO, W.
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[151] DAVIS, A. R. Orr-line gap det
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[177] COOK, G. E. Feedback and adap
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[201] WON, Y. J. and CHO, H. S. A f
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220
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222
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wnum: local variable which defines
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Table A. 1 - continuation List item
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Imean = a2 + b2*WFS + c2*SO + d2*SO
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TCP2 number are also defined. The o
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f ROBSET. DAT: This file is created
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Figure C. 3 - Main dialogue box of
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Choose the set of welding parameter
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Water Cooling optic fibre bundle 0
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Figure E. 1 - Main graphical screen
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242
Page 269 and 270:
Table G. 2 - Interface box external
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Robot ii Controller +24W CO . +24Vd
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248
Page 275 and 276:
Table 1.1 - continuation Run Vpk M
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10- y =0.001ac 0 r. dSO [mm] $0 '10
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5.00- 0.00 y=0.0019x 1000 1500 2000
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Table J. 7 - Welding data collected
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Table J. 10 - Welding data collecte
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Page 287 and 288:
20.00- 15. M y=0.0047x - 1.7922 10.
Page 289 and 290:
Page 291 and 292:
266
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Table K. 1- continuation Set-up par
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Table K. 1 - continuation Set-up pa
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Table K. 2 - continuation Set up pa
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Table K. 2 - Continuation Set-up pa
Page 301 and 302:
Table K. 3 - Continuation Set-up pa
Page 303:
Table K. 3 - Continuation Setup par
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