SYSTEM DEVELOPMENT FOR ANALYSIS OF GAS TUNGSTEN ARC WELDING By Anna Katherine Albrecht Thesis Submitted to the Faculty of the Graduate School of Vanderbilt University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE in Electrical Engineering May, 2006 Nashville, Tennessee Approved: Date: George E. Cook Alvin M. Strauss ACKNOWLEDGEMENTS I would like to thank all those with whom I have had the pleasure to work, especially, Dr. George E. Cook for his guidance and dedication. This work would not have been possible without him. I also would like to thank Dr. Strauss for his guidance. I really enjoyed working with everyone. This experience has taught me more than I ever thought it would. I also would like to thank Dr. Francis Wells for his help throughout all my educational plans. He supported me in my decision to go to graduate school. Without him, I would not be writing this. I will always remember my experiences, friends, and associates whom I have met while at Vanderbilt University. ii TABLE OF CONTENTS Page ACKNOWLEDGEMENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ii LIST OF FIGURES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . v LIST OF TABLES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xi NOMENCLATURE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xii Chapter I. INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1 Problem Statement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 Approach . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 Equipment: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 Welding Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 Imaging System and Macro Lens System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3 II. BACKGROUND . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5 Gas Tungsten Arc Welding Process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5 Advantages and Disadvantages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9 Power Source . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9 Alternating Current (AC) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 Direct-Current Electrode Negative (DCEN) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 Direct-Current Electrode Positive (DCEP) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 The Electrode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 Electrode Material . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .13 2% Thoriated Tungsten . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 2% Ceriated Tungsten . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 1½% Lanthanated Tungsten . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .15 Zirconiated . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 Pure Tungsten . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 Electrode Diameter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 Grind Angle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17 Tip Diameter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 Joint Types and Positions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .20 Geometry of Weld Bead . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 Weld Pool Shape . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 Shielding Gas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 Argon . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 Helium . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 Argon-Helium Mixtures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 Argon-Hydrogen Mixtures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 Multi Input Output System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 Automatic Voltage Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 Applications of GTAW and Welding Automation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 Digital Camera . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .33 Lens Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .42 Digital Image Processing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .45 iii Basic Image Processing Techniques . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .47 Filtering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .49 Gradient and Laplacian Filters. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53 Smoothing Filters and Edge Enhancement Filters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .57 Fourier Transform . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61 Optimal and Sub-optimal Filters. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .68 Fourier Domain Correlation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69 Fast Fourier Transform . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71 High Speed Imaging System and Macro Lens Viewing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .72 Digital Camera and Macro Lens System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72 Image Acquisition Board and Software . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76 III. EXPERIMENTAL METHOD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79 Welding Parameters for the Gas Tungsten Arc Welding System . . . . . . . . . . . . . . . . . . . . . . . . . .79 Signal and Image Acquisition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .81 IV. HIGH SPEED DIGITAL IMAGING SYSTEM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83 Viewer Program . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83 Spatial Filters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87 Convolution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88 LabVIEW Programming Definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89 V. RESULTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95 VI. DISCUSSION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96 VII. CONCLUSIONS AND RECOMMENDATIONS FOR FUTURE WORK . . . . . . . . . . . . . . . . . . . . . . . 98 APPENDIX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100 A. LabVIEW Programs and Overview of Welding Process. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100 B. Dalsa Camera Data Sheets. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107 REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .109 iv LIST OF FIGURES Figure Page 1. The GTAW process. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 2. GTAW process with an optional optical probe to collect specular reflections of the weld pool’s surface. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 3. The GTAW circuit. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 4. Gas tungsten arc welding: (a) overall process (b) welding area enlarged. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 5. GTAW Electrode Polarity. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 6. Diagram of the electrode showing diameter, tip diameter, and included angle. . . . . . . . . . . . . . . . . . . . . . . . . . .17 7. Arc shape and fusion zone profile as a function of electrode included angle. . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 8. Welding positions and primary joints. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 9. Comparison of weld pool shapes under different travel speeds and the average grain growth direction. under different heat source travel speeds. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 10. Comparison of weld pool shapes and grain growth under different travel speeds. . . . . . . . . . . . . . . . . . . . . . . . 24 11. The different classifications of penetration. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .25 12. Variation of heat input to the workpiece with power density of the heat source. . . . . . . . . . . . . . . . . . . . . . . . . 26 13. Arc welding depicted as a multiple-input, multiple-output system. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 14. CCD architectures with different arrangements of image section and storage section: full frame transfer, interline transfer, and frame transfer. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34 15. Spectral sensitivity of silicon and the human eye. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .38 16. Spectral characteristics of the red, green, and blue filters used in RGB color cameras. . . . . . . . . . . . . . . . . . . . . 38 17. Test pattern with different realizations of γ (γ = 0.6, 1.0, 1.6 from left to right). . . . . . . . . . . . . . . . . . . . . . . . . . 39 18. Lens selection. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 19. Diagram of a lens system. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45 20. A simple digital image: (a) The image and (b) the corresponding array of numbers. . . . . . . . . . . . . . . . . . . . . . 48 21. Form of a typical point spread function h(t). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51 22. Digital Convolution: The output at a point is given by the sum of the input values around the point, each multiplied by the corresponding term of the h array. To compute the next v output value, the h array is shifted, and the multiply and sum operation repeated . . . . . . . . . . . . . . . . . . . . . . . 52 23. The Laplacian as pushing a pixel away from its neighbors. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59 24. The definitions for the forward and inverse transforms for each of these cases (The three letters starting at each line indicate Continuous/Discrete, 1 dimension or 2, and Forward or Inverse transform). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63 25. Comparison of standard and optical transforms: (a) The standard form of the Fourier transform in upper left, and (b) the transform rearranged into the optical form in upper right. (c), in lower left, shows the origin and coordinate systems for the two forms. The reordering to convert from one to the other in two dimensions is shown in (d). . . . . . . . . . . . . . . . . . . . . . . . . . 67 26. Comparison of multiplication operations using spatial and Fourier correlation. . . . . . . . . . . . . . . . . . . . . . . . . . 70 27. Photograph showing the overall layout of the macro camera system. The digital camera and the associated computer hardware is shown in the upper left area of the picture. . . . . . . . . . . . . . . . . . . . . . 73 28. Macro camera imaging system showing linear array and digital frame grabber camera . in position for measurements Camera magnification is 28.86x. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74 29. The Dalsa CA-D1-0128A camera. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .75 30. Photograph showing the orientation between the macro camera. the GTAW torch and the workpiece. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76 31. The IMAQ library palette shows basic, advanced, and color VIs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78 32. Program used for saving images from camera system. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82 33. The main program which calls each subsequent programs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84 34. Window of the program used to open images to be used by the viewer program. The block diagram can be seen in the appendix. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85 35. The Front Panel of the LabVIEW Viewer Program. Note: Begin 40 19 122, End 8 34 0, Gradient 74 71 255 The last number is cut off in the image. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86 36. Portion of LabVIEW Viewer Program Showing Convolution of the Image. . . . . . . . . . . . . . . . . . . . . . . . . . . . 92 37. Portion of Labview Program Showing the Spreadsheet Command. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93 38. Front panel and block diagram of the LabVIEW subprogram used to get pixel data over each frame from the original image. Index and Index 2 corresponds to the coordinates of the pixel. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94 39. This is frame number 48 out of the 1800 frames in the image, 79d.log. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95 vi LIST OF TABLES Table Page 1. Commonly Available Tungsten Electrodes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 2. Commercially sold tungsten types, their American Welding Society (AWS) and International. Standards Organization (ISO) classifications, and the amount and type of oxide contained in the electrode. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 3. Advantages and disadvantages of electrode tip diameters. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 4. Advantages and disadvantages of electrode tapers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 5. Properties of shielding gases used for welding. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 6. Gas Tungsten Arc Welding parameters for the welds (images of the welds) obtained. . . . . . . . . . . . . . . . . . . . . . 81 vii Welding Terminology Acetone A flammable, volatile liquid used in acetylene cylinders to dissolve and stabilize acetylene under high pressure. Acetylene A highly combustible gas composed of carbon and hydrogen. Used as a fuel gas in the oxyacetylene welding process. Air-Acetylene A low temperature flare produced by burning acetylene with air instead of the carbon arc. Alloy A mixture with metallic properties composed of two or more elements, of which at least one is a metal. Alternating current An electric current that reverses its direction at regularly recurring intervals Arc length The distance between the tip of the electrode and the weld puddle Arc voltage the voltage across the welding arc Arc welding A group of welding processes in which fusion is obtained by heating with an electric arc or arcs, with or without the use of filler metal. As welded the condition of weld metal, welded joints, and weldments after welding and prior to any subsequent thermal, mechanical, or chemical treatments. Bare electrode An arc welding electrode that has no coating other than that that incidental to the drawing of the wire. Base metal The metal to be welded or cut. In alloys, it is the metal present in the largest proportion. Bead weld A type of weld composed of one or more string of weave beads deposited on an unbroken surface. Beading see string bead welding and weave bead. Bevel Angle The angle formed between the prepared edge of a member and a plane perpendicular to the surface of the member. Buckling Distortion caused by the heat of a welding process Buildup sequence The order in which the weald beads of a multipass weld are deposited with respect to the cross section of a joint. viii Case hardening A process of surface hardening involving a change in the composition of the outer layer of an iron base alloy by inward diffusion from a gas or liquid, followed by appropriate thermal treatment. Typical hardening processes are carbonizing, cyaniding, carbonitriding, and nitriding Coated electrode An electrode having a flux applied externally by dipping, spraying, painting, or other similar methods. Upon burning, the coat produces a gas which envelopes the arc. Covered electrode A metal electrode with a covering material which stabilizes the arc and improves the properties of the welding metal. The material may bean external wrapping of paper, asbestos, and other materials or a flux covering. Crater depression at the termination of an arc weld Critical Temperature The transition temperature of a substance from one crystalline form to another. Concavity The maximum perpendicular distance from the face of a concave weld to a line joining the toes. Current density amperes per square inch of the electrode cross sectional area Cylinder A portable cylindrical container used for the storage of a compressed gas. Defect A discontinuity or discontinuities which, by nature or accumulated effect render a part or product unable to meet the minimum applicable acceptance standards or specifications. This term designates rejectability. DCEN Direct current electrode negative The arrangement of direct current arc welding leads in which the work is the positive pole and the electrode is the negative pole of the welding arc DCEP direct current electrode positive The arrangement of direct current arc welding leads in which the work is the negative pole and the electrode is the positive pole of the welding arc Depth of fusion distance from the original surface of the base metal to that point at which fusion ceases in a welding operation Drag The horizontal distance between the point of entrance and the point of exit of a cutting oxygen stream. Duty Cycle The percentage of time during an arbitrary test period, usually 10 minutes, during which a power supply can be operated at its rated output without overloading. Electrode holder A device used for mechanically holding the electrode and conducting current to it. Joint Penetration ix The maximum depth a groove weld extends from its face into a joint exclusive of reinforcement The temperature at which a metal begins to liquefy melting point Melting range temperature range between solidus and liquidus Melting rate the weight or length of electrode melted in a unit of time Pass the weld metal deposited in one general progression along the axis of the weld Reverse polarity the arrangement of direct current arc welding leads in which the work is the negative pole and the electrode is the positive pole of the welding arc Slag inclusion non-metallic solid material entrapped in the weld metal or between the weld metal and the base metal String bead A method of metal arc welding on pieces ¾ in. (19mm) thick or heavier in which the weld metal is deposited in layers composed of strings of beads applied directly to the face of the bevel. Solidus is the highest temperature at which a metal or alloy is completely solid Spall small chips or fragments which are sometimes given off by electrodes during the welding operation. This common with heavy coated electrodes Spatter the metal particles expelled during arc and gas welding which do not form a part of the weld Straight polarity the arrangement of direct current arc welding leads in which the work is the positive pole and the electrode is the negative pole of the welding arc. Temper colors colors which appear on the surface of steel heated at low temperatures in an oxidizing atmosphere Toe of the weld The junction between the face of the weld and the base metal. Undercutting An undesirable crater at the edge of the weld caused by poor weaving technique or excessive welding speed. Weave bead type of weld bead made with transverse oscillation Weld a localized fusion of metals produced by heating to suitable temperatures pressure and/or filler metal may or may not be used. The filler material has a melting point approximately the same or below that of the base metals, but always above 800 degrees F (427C) Weld bead weld deposit resulting from a pass Weld gauge a device designed for checking the shape and size of welds Weldment is a unit composed of an assemblage of pieces welded together. Weld metal that portion of a weld that has been melted during welding x