ORIGINAL ARTICLE Study on automatic control of arc gap in robotic TIG welding Mohammad Reza Karafi & Ramin Narimani & Yousef Hojjat & Mojtaba Gheybi Received: 19 October 2008 / Accepted: 3 February 2010 / Published online: 6 March 2010 # Springer-Verlag London Limited 2010 Abstract This paper presents a method for automatic control of arc length in tungsten inert gas (TIG) welding process using the arc voltage. By using this method, the role of operator in arc length control is played by an automatic control system based on a predefined arc voltage value for any special welding operation. A dynamic model for feed-rate mechanism and the relation between variations of arc length and voltage are described in details. Using a proportional-integral controller, variations of arc length in welding path is compensated with an automatic feed-rate mechanism in a normal direction to the welding path. By keeping the voltage constant during the process, a stable weld with higher quality and better appearance is obtained specially in welding of uneven surfaces. Theo- retical and practical investigations show that the sug- gested method is able to control the TIG welding process successfully. Test results show that an accurate weld is obtained without the interference of the operator, and by comparing the predefined values of arc voltage with what is practically obtained, the welding gap is automatically adjusted. Keywords TIG welding . Control . Arc length . Tungsten . Automation 1 Introduction Welding is a basic method for joining materials, which is very important in manufacturing industries, and automation of welding processes is widely considered by different industries because intelligent and automated welding is crucial in improving productivity, decreasing production costs, and improving the safety of working environment [1]. Gas tungsten arc welding (tungsten inert gas (TIG)) is known for its high weld quality and low pollution and is widely used in practices such as vessel and pipe welding. Automation of TIG welding could promote its development in industry [2]. In particular, all-position TIG welding has not been devel- oped to a great degree [3]. To develop an automatic welding control system that could replace manual welding, the main challenge is the control of arc length in welding, in order to preserve the arc stability during the welding process. In conventional TIG welding process, the skilled operator tries to keep the arc length constant. By using the robotic system, the role of operator in arc length control is played by an automatic control system, which is the main goal of the study. Welding performance can be improved by appropriate inverter control methods [4]. Different control methods have been proposed. More desirable welding performance can be achieved by incorporating an instantaneous arc voltage control. However, its implementation into an actual welding system is complex, since it requires an optimum arc voltage reference input and sophisticated adjustment of the voltage controller. To obtain a stable welding process, it is important to choose the appropriate welding parameters, such as the arc current and arc voltage. In a TIG welding process, a relatively small variation in the arc length, ranging from a few millimeters to a few tenths of millimeters, will induce enormous arc voltage fluctuations, which may exceed the maximum allowable range of the power source. Therefore, M. R. Karafi (*) : Y. Hojjat : M. Gheybi Mechanical Engineering Department, Tarbiat Modares University, Tehran, Iran e-mail: karafi@modares.ac.ir R. Narimani Mechanical Engineering Department, University of Science and Technology, Arak, Iran Int J Adv Manuf Technol (2010) 50:953–960 DOI 10.1007/s00170-010-2564-z