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8.2.2 Integration between geometrical design and weld design In order to illustrate how the geometrical data available in the component CAD drawings could be used to generate positional data for off-line programming and how welding models could be used to generate welding procedures, a special program, written in AutoLisp programming language, was developed to be utilised as an AutoCAD application. The program was designed for linear fillet joints and consists of two main modules: (a) welding parameters generator and (b) robot programming module. Both modules and the algorithms used in the modules are fully described in sections 3.3.2.1 and 3.3.2.2. The welding parameters generator uses an adaptation of the algorithm developed by Ogunbiyi [ref. 51] to predict welding parameters which are expected to produce the required weld quality. It outputs a list containing all the possible combinations of welding parameters which are expected to produce the required quality, giving the user the option of selecting the preferred combination based on criteria such as possible risk of defects (e. g. undercut) or productivity requirements (e. g. minimum welding speed). The algorithm in this work was implemented in a flexible way that allows the use of different coefficients for the welding models. Each set of coefficients is stored in a specific file, in a special format (see Appendix B). Before the user starts defining a weld, he must choose the set of coefficients (defined by the combination of shielding gas, wire type, jigging system and power source), which correspond to the actual welding cell. Ideally, this means that new model coefficients should be obtained for each different combination, implying more welding trials. This could be viewed as a restriction to the implementation of the method. However, the process controller developed in this work incorporates an automatic voltage tuning algorithm designed to optimise the welding voltage (see sections 4.2 and 7.1), which means that fewer welding trials would be needed to develop new welding procedures, even if different power sources, welding wires and shielding gas types were used [refs. 35,199]. Also, based on conclusions from previous work by Luijendijk and Hermans [ref. 29], which state that for Argon rich gases with 5% to 20% CO2 there are no significant changes in the short circuiting frequency and deposition rate, it could be assumed that no further welding trials would be necessary to define new coefficients for gases in this range (Ar +5% to 20% C02), if all the other variables are kept constant. 8.2.3 Extraction of positional data for off-line programming The advantage of integrating the off-line programming into the CAD system is that it makes it possible to directly extract the joint geometry data' and transform it into a suitable robot path. The software developed in this work used the solid modelling techniques provided by the AutoCAD Modelling Extension (AME) to define the weld joint. The joint line was obtained by extracting the geometrical data from the intersection line between two adjacent semi-planes which formed a fillet joint. i Joint position and orientation, joint length and start and end points. 189
Although only linear joints were implemented in this work, it should be noted that non-linear joints could also be included for off-line programming by sub-dividing the non-linear curves obtained from the intersection between two adjacent surfaces into small linear segments and treating these as a series of successive linear joints. This could increase the application scope of the program to deal with, for example, fillet welds in pipe sections. It should also be noted that the currently available robots are limited to linear and circular interpolation. That is, they can only perform ruled paths either passing through specified points in the form of a line between two teach- points or an arc passing through a third teach-point located between the teach-points which define the start and end of the arc. Hence, a non-linear non-circular robot path can only be defined as a series of successive linear paths with the torch orientation changing linearly between the teach-points. The benefit of integrating the welding procedure generation and the geometrical data extraction for off-line programming into the CAD software is that the resulting welding data2 and the weld positional data3 can be stored in the same CAD drawing file in the form of data associated with the line segment which defined the weld joint. Therefore, if a different welding cell and robot is used, the only modification needed for generating the new robot teach-points would be the definition of the CAD-to-Robot transformation matrix. It should be noted that the definition of this transformation matrix depends on a set of points which are located using the robot. The orientation of the torch relative to the joint line was set by default as being perpendicular to the joint line at the point being defined (start or end point) and contained in the joint bisection plane. For example, for a 90 deg included angle flat position fillet joint, the default orientation would be parallel to the gravitational vector. This orientation could be changed by the user if required. Also, an offset for the position of the weld start and end points along the joint line was introduced to ensure that there would always be base material to receive the weld metal. No transversal tolerance was allowed, however this could be easily implemented. This could be necessary for welding steels with different heat sink characteristics in each side of the joint. The rules used to generate the orientation necessary for the welding torch to achieve different joint approach and withdrawing directions were devised from prior on-line programming experience of a welding robot with a specific torch configuration. Therefore, for a different robot/welding torch combination, a modification in the angles of the planes defining the different orientation regions would be necessary (see section 3.3.2.2). The teach-points defining the welding torch approach and withdrawing paths relative to the joint were generated based on the assumption that the component, once fixed in the jigging system, would not be moved until the completion of the welding operation. This implies that the component clearance box (see section 3.3.2.2) would also be fixed and, therefore, the approach and withdrawing points and vectors. However, different rules could be defined in situations where the component 2 Required welding quality and chosen welding procedure 3 Relative to the CAD coordinates frame. 190
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CRANFIELD UNIVERSITY GC CARVALHO AN
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ABSTRACT The aim of this work was t
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I dedicate this work to the memory
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FIGURES TABLES APPENDICES NOTATION
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3.3.2.1 Welding parameters generato
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References Further reading Appendic
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Figure 3.12 Offsets for weld start
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Figure 6.31 Voltage step input test
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Figure J. 2 Plot of stand-off varia
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Table A. 1 Welding extended entity
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NOTATION A, Electrode sectional are
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Pr(ign) Possibility measure of proc
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1. Introduction Welding is the thir
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Chapter 4 describes the on-line pos
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In pulse transfer, the welding curr
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Pd = Pv - pzh-s (2.1) where Pd is t
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the bridge. Another factor that ind
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establish the stable conditions for
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Philpott [ref. 21] developed an on-
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current peak at the moment the tip
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obot on the line must be individual
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collision detection capabilities wh
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cause dynamic variation in the seam
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Another type of robot static calibr
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spatter the gas nozzle is particula
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Table 2.1: Joint positioning tolera
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In order to minimise the undesirabl
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c) Ultrasonic sensors; d) Through-t
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where K,, K2, K3 and K4 are constan
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Philpott [refs. 21,131], based on t
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centre. This is attributed to the m
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technique must be employed to preve
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" digital hardware, which is basica
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" Maximum value, W.: Wmý = max(W )
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process studied over a small range.
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In-process welding control is a muc
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volume caused by the presence of a
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SHIELDING GAS IN CONSUMABLE ELECTRO
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Arc voltage Anode Arc length I Anod
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computed ideal procedure optimisnti
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CONSTANT CURRENT POWER SOURCE `j' O
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Original Surface New Surface Electr
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otating welding wire direction weld
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3.1.1.1 Robot errors A robot arm is
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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
Page 163 and 164: stickout lengths and the temperatur
Page 165 and 166: of the dip mode of metal transfer.
Page 167 and 168: which would become active by settin
Page 169 and 170: In section 4.2.5 it has been mentio
Page 171 and 172: 300 280 260 240 rd 35- 3D 25 20 15
Page 173 and 174: Figure 6.5 - Measured "versus" Pred
Page 175 and 176: i S 0 -0.1 -0.2 -0.3 -0.7- 68 10 12
Page 177 and 178: 32.0 E 31.5 y 31.0 30.5 30.0 j 29.5
Page 179 and 180: 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
Page 183 and 184: 30 28 26 24 22 SO_act [mm] DipR [mo
Page 185 and 186: 22 20 18 SO_act [mm] DipR [ohm/100]
Page 187 and 188: !: 30 25 20t 10 5-- 0 Dip Transfer
Page 189 and 190: 0.430- - 0.380- - :r 0.330 fPR L- 0
Page 191 and 192: 7.2 Tests with varying stand-off an
Page 193 and 194: Table 7.3 - Bead geometry along the
Page 195 and 196: ö a2 ., u" u,.., g .,. aucyuaac VI
Page 197 and 198: 0 24-- 22-- 18 210 1 90 0 v 170 mm
Page 199 and 200: Q 34 32 3o mIm Viewing direction Fl
Page 201 and 202: ýa 34 mm JO a .. ý nn ýr "u 00 M
Page 203 and 204: 22 20 18 Viewing direction Flange W
Page 205 and 206: 36 33 31 o 29 t 350 310 o 290 U due
Page 207 and 208: I C, x -i 23 21 j 19 Q 240c WFS =10
Page 209 and 210: en 34 32 - vsec 30- 26- 24 + .. ++
Page 211 and 212: 186
Page 213: " to design and build the hardware
Page 217 and 218: for predicting possibility of bad a
Page 219 and 220: 8.4 Process monitoring and control
Page 221 and 222: satisfy the required quality criter
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Page 225 and 226: types of joints and multi-pass weld
Page 227 and 228: [14] NEMCHINSKY, V. A. The effect o
Page 229 and 230: [38] D1LTHEY, U. , REICHELL, T. , S
Page 231 and 232: [64] KING, F-J. and HIRSCH, P. Seam
Page 233 and 234: [86] CARGNELLI, M. and ROGOWSKI, A.
Page 235 and 236: [109] KURKIN, N. S. and DRIKKER, V.
Page 237 and 238: [130] USHIO, M. , LIU, W. , MAO, W.
Page 239 and 240: [151] DAVIS, A. R. Orr-line gap det
Page 241 and 242: [177] COOK, G. E. Feedback and adap
Page 243 and 244: [201] WON, Y. J. and CHO, H. S. A f
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Page 249 and 250: wnum: local variable which defines
Page 251 and 252: Table A. 1 - continuation List item
Page 253 and 254: Imean = a2 + b2*WFS + c2*SO + d2*SO
Page 255 and 256: TCP2 number are also defined. The o
Page 257 and 258: f ROBSET. DAT: This file is created
Page 259 and 260: Figure C. 3 - Main dialogue box of
Page 261 and 262: Choose the set of welding parameter
Page 263 and 264: Water Cooling optic fibre bundle 0
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Figure E. 1 - Main graphical screen
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242
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Table G. 2 - Interface box external
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Robot ii Controller +24W CO . +24Vd
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248
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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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20.00- 15. M y=0.0047x - 1.7922 10.
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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
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Table K. 3 - Continuation Set-up pa
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Table K. 3 - Continuation Setup par
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