A Passive Imaging System for Geometry Measurement for the Plasma Arc Welding Process

Abstract

Automatic and flexible geometry measurement of the weld pool surface can help better understand the complex welding processes and even provide feedback to better control this process. Most of existing imaging systems use an additional source of illumination to remove the light interference coming from the welding arc but it is usually costly. This paper introduces a novel low-cost optical-sensor-based monitoring system working under passive mode to monitor the wire + arc additive manufacture process, particularly for plasma arc welding. Initially, configurations and parameters of camera are investigated to achieve good visualization of weld pool. A novel camera calibration methodology using the nozzle of a computer numerical control (CNC) machine is then proposed for this imaging system, allowing estimation of the camera position with respect to the inspecting surface and its orientation in an easy-to-use approach. The verification tests show that the average error of the calibration is less than 1 pixel. As a case study, an image analysis routine is proposed to measure the width of the bead during the welding process. The results show that the proposed system is effective to measure the dimension of weld pool. Index Terms-Additive manufacturing (AM), camera calibration, edge detection, plasma arc welding (PAW), wire + arc additive manufacture (WAAM). I. INTRODUCTION A DDITIVE manufacturing (AM) is a process of threedimensional (3-D) printing in which parts are built by adding materials layer by layer. Compared to traditional subtrac

Current Status and Perspectives on Wire and Arc Additive Manufacturing (WAAM)

“…Traditionally, in fusion welding, monitoring is made through an evaluation of current, voltage, shielding gas flow rate, travel speed, and wire feed speed. In addition, during WAAM, sensors can be used to monitor the temperature at different regions [151], measure the size and geometry of beads [152,153], determine the weld pool characteristics, monitor the acoustic signal of deposition [154], detect electrical conductivity variations [155], and measure oxygen levels [156]. Normally, in fusion-based welding, the process parameters are held constant, but in WAAM, due to differences of thermal behavior throughout parts fabrication, geometric variations and mechanical properties are established and adjustments are necessary.…”

Building an Omnidirectional 3-D Color Laser Ranging System Through a Novel Calibration Method

“…Camera calibration is the process of determining the internal geometric and optical characteristics of a camera (intrinsic parameters) and/or the position and orientation of a camera relative to a world coordinate system (extrinsic parameters) by only using 2D images from the camera [5].…”

“…Later, he also proposed another camera calibration technique based on 1D calibration objects [11]. Recently, Font comas et al [5] presented a camera calibration methodology by using a checkerboard pattern for a passive imaging system.…”

Measurement and estimation of the weld bead geometry in arc welding processes: the last 50 years of development

“…Among the methods proposed in the available literature [4][5][6], vision sensing is one of the promising solutions. The use of video cameras to measure the weld bead width and reinforcement is possible, as shown in [7][8][9][10][11]. These methods need optimal light conditions and are difficult to applicate in the industrial environment.…”