Welding Journal - April 2012 - (Page 101-s)

SUPPLEMENT TO THE WELDING JOURNAL, APRIL 2012 Sponsored by the American Welding Society and the Welding Research Council Arc Characteristics in Pulse-GMA Welding with Acute Groove Angles An arc sensor system was investigated for welding a V-groove joint with acute groove angles of 45 and 60 deg by considering the arc characteristics in pulsed GMA welding BY R-H. KIM, G-D. CHOI, C-H. KIM, D-W. CHO, AND S-J. NA ABSTRACT This paper presents the experimental results of arc characteristics in pulsed GMA welding with acute groove angles of 45 and 60 deg. Electrical signals of current and voltage were measured, while the arc behavior was observed by using a high-speed camera, and their relations were investigated and analyzed to provide data that may be used for automatic joint tracking in future research. By understanding the arc characteristics, appropriate threshold current could be determined for electrode turning in a weaving-type arc sensor for pulsed GMA welding in acute groove angles. Introduction With automation of the welding process, a wide variety of sensors are used to detect and track the weld joint, and to monitor the welding phenomena. In particular, tactile, vision, and arc sensors are widely used for automatic weld joint tracking (Ref. 1). Among these sensors, the arc sensor is utilized in measuring the voltage and current of welding arcs and coaxially tracking the joints and monitoring weld quality. Various studies have been carried out, primarily on a DC welding power source for gas metal arc welding (GMAW) (Refs. 2–5). In more recent studies, a new algorithm has been applied to existing arc sensors. Ahn et al. utilized the changes in welding current by the contact tip-toworkpiece distance (CTWD) to more closely examine the arc sensors that are free from weaving (Ref. 4). Kim et al. tracked the weld joints by comparing the changing patterns of welding current, observed in weave welding, thereby obtaining the information on weld joints (Ref. 5). Pulsed GMA welding was developed in R-H. KIM and G-D. CHOI are with Department of Welding Research, Industrial Research Institute, R&D division, Hyundai Heavy Industries, Jeonha-Dong, Dong-Gu, Ulsan, Republic of Korea. C-H. KIM is with Advanced Joining Technology Team, Songdo-Dong, Yeonsu-Gu, Incheon, Republic of Korea. D-W. CHO and S-J. NA (sjoona@kaist.ac.kr) are with Department of Mechanical Engineering, KAIST, Daehak-ro, Yuseong-gu, Daejeon, Republic of Korea. 1960 to address the disadvantages of globular transfer and to take advantage of spray transfer. The most distinctive feature of this method is that it takes the form of a pulse that has the welding current consisting of peak and base current, and thus its average current has a lower value than the transition current of spray transfer. In this case, the base current retains the welding arc while the peak current is maintained for a sufficient period of time so that droplets can be transferred (Ref. 6). Each time the pulse current is applied, one droplet is transferred from the welding electrode to the base metal to maintain the control of metal transfer. Compared to the DC GMA welding power source, less heat input is applied to the base metal, and regular metal transfer enhances the quality of the weld joint (Ref. 7). Welding current values measured in the form of continuous wave (CW) are primarily used in the conventional, constant voltage type of DC GMA welding. Pulsed GMA welding, meanwhile, has a greater number of current-waveform parameters as it involves the peak current and base current KEYWORDS GMAW-P Acute Groove Angle Arc Characteristics Arc Sensor V-Groove Joint (Ref. 8). The power source of pulsed GMAW is widely used in the form of constant current, constant voltage, and a combination of these two forms, while a synergic control and other methods are utilized to control the pulse waveform. For this reason, the use of an arc sensor is not feasible in the existing normal context. Previous studies have applied the arc sensors to certain types of welding power sources, capitalizing on the feature that the peak current or pulse period changes linearly with CTWD. However, little research has been done on the application of the arc sensor to various types of weld joint shapes (Ref. 9). In order to achieve complete penetration of a thick plate, the root opening and groove angle must be adequately selected in the process of welding a butt joint. The deposited metal decreases and productivity increases when the groove angle becomes smaller, but the preceding of the weld pool results in weld defects such as incomplete penetration at the groove face. For this reason, a wide range of groove shapes is tailored to different welding conditions. When the groove joint is welded by weaving, the arc shape differs according to the groove angle and the self-regulation effect of the welding arc by the weaving speed and groove angle, thereby affecting the patterns of the welding signal. Therefore, in an endeavor to identify the arc sensor characteristics for tracking weld joints in pulsed GMA welding, the groove angle and root opening for a Vgroove joint were varied to perform weave welding, and the characteristics of the arc shape and current waveform were examined. Experimental Setup This study utilizes a biaxial stage to move the electrode and an inverter-type synergic pulse-type welding power source, for which an embedded microprocessor controls the pulse parameters. A hall senWELDING JOURNAL 101-s WELDING RESEARCH

Table of Contents for the Digital Edition of Welding Journal - April 2012

April 2012 - TOC Listing
Unlocking Your Gas Metal Arc Welding Potential - A study sponsored by the National Shipbuilding Research Program investigated low-cost modifications to equipment or parameters that improved welding performance - P. A. Blomquist
Community College Welding Program Update - Many community colleges around the country are equipping future workers with the skills manufacturers need D. Postlethwaite
Modern Power Source Technology Drives Process Improvement - New technology in weld monitoring is making it easier to access the data by all the appropriate personnel and understand how it should be applied to benefit weld quality - T. McEllis
Building a Welding Career from the Ground Up - A thirty-two-year career welder shares her passion for the profession with others in hopes of inspiring them to expand their skills and knowledge
How Today’s Power Sources Aid Pulsed GMAW - The advanced welding machines of today can deliver power to the arc in almost any form and can react with split-second timing to avoid adverse arc phenomena - L. Barley
Fiber Lasers Perform Precision Cutting for Medical Devices - There are many methods to cut thin tubular structures often used in medical devices, but fiber lasers are emerging as the precision machines of choice
Arc Characteristics in Pulsed-GMA Welding with Acute - Groove Angles The characteristics of a joint tracking sensor were monitored under conditions of different groove angles and root openings - R-H. Kim et al.
Design of Experiment and Goal Programming Application for the GMAW Process - This study was conducted to determine critical gas metal arc welding variables and ways to optimize them - Y. T. Iç et al.
Predictive and Measurement Methods for Delta Ferrite Determination in Stainless Steels - The advantages and limitations of predictive measurement methods for δ ferrite are outlined - M. A. Valiente Bermejo
Susceptibility of IN740 to HAZ Liquation Cracking and Ductility-Dip Cracking - Conditions that lead to cracking susceptibility of nickel-based IN740 were simulated to determine an action for its prevention - J. E. Ramirez
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Welding Journal - April 2012