VOL. 15, NO. 5, MARCH 2020 ISSN 1819-6608 ARPN Journal of Engineering and Applied Sciences ©2006-2020 Asian Research Publishing Network (ARPN). All rights reserved. www.arpnjournals.com 607 OPTIMIZATION OF HIGH-FREQUENCY RESISTANCE WELDING PROCESS USING MECHANICAL PROPERTY OF FINNED TUBE SA-192 STEEL Montri Sangsuriyun 1 , Prayoon Surin 1 and Krittee Eidhed 2 1 Department of Advanced Manufacturing Technology, Faculty of Engineering, Pathumwan Institute of Technology, Bangkok, Thailand 2 Faculty of Engineering, King Mongkut’s University of Technology North Bangkok, Bangkok, Thailand E-Mail: montri.sang@npuac.th ABSTRACT The objective of this study is to investigate the effects of welding parameters in the welding process on the mechanical properties and micro structure to compare the design of experiment (DOE) for the high-frequency resistance welding process (HFRW) of ASTM SA-192high-carbon steel. The different butt weld T joints of finned-tubes were prepared by varying the welding parameters, including current (A), voltage (kV) and frequency (rpm) which were also related to the heat input and mechanical properties. DOE analysis of the welding parameters was performed at 9A, 13kV, 250 rpm and heat input of 474 J/mm. The results showed that the ultimate tensile strength was 749 MPa which meets the standard requirements of the Association of Finned Tube Manufacturers and is at a good level in the production viewpoint.However, the examination of the micro-and macrostructure of the weld line using an inverted microscope showed some melting on the specimens and it was found that some specimens had high weld width and weld depth. In addition, the tensile strength was also higher . However, too high tensile strength was changed the material structure, the cause of HAZ. Through the validation of the welding process which was compared to the fatigue strength, the following results were indicated: (1) the ultimate tensile strength at the highest tensile stress was not the ultimate fatigue strength and the heat input affected the weld width and weld depth of the weld line . (2) In the welding process, the weld width and weld depth must be also considered since they can affect the specimen failure during the experiment . Therefore, extreme care must be taken when using a high-frequency resistance welding process. Keywords: welding parameters, mechanical property, resistance welding process, finned-tubes. 1. INTRODUCTION There are many types of stainless-steel heat exchangers, such as shell and tube heat exchanger, plate heat exchanger and finned tube heat exchanger, etc. The finned tube heat exchanger is widely used and has a variety of applications in industries such as oil refineries, power plants and petrochemical industry due to the advantages of a finned pipe which can improve heat dissipation by increasing heat transfer surface area. Thus, it reduces the number of pipes and related equipment sizes, which can also reduce project costs [1]. The high- frequency resistance welding (HFRW) process is considered as the resistance welding that uses high- frequency current in the welding process. HFRW can generate heat and relies on the compression force in welding the specimen. Besides, controlling the welding speed results in heat conduction during the welding process, which affects the weld depth of the material. If the welding speed decreases, the heat inside the specimen increases, increasing the weld depth of the material [2, 3]. A common problem in the heat exchange of stainless steel is the cracks in the tube and the fin surface. These cracks are caused by stress corrosion cracking (SCC). Local stress level resulting from the combination of loads affects the fracture in the material. Although stainless steel has excellent resistance to fatigue or corrosion, high heat or temperature in the welding process can lead to cracks and risk of corrosion. SCC is induced by stress along with the exposure of the corrosive environment [4, 5, 6]. In addition, fatigue caused by external forces and vibration due to the environment affects the optimization of welding parameters or welding processes, because unsuitable parameters accelerate cracking and corrosion [7, 8]. Therefore, this study aimed at determining the optimum parameters by using the Design of Experiment (DOE) principle for the high-frequency resistance welding process and the comparison the mechanical properties of the material, including tensile stress, fatigue and macro- and microstructure of SA-192 finned tube, the causes of failure in welding of pipe and fin. 2. EXPERIMENTAL PROCEDURE 2.1 Materials and welding standards In this study, the finned tube heat exchanger was investigated. This heat exchanger was made of ASTM SA- 192 high-carbon steel with 0.6-0.18% C, 0.27-0.63% Mn, 0.25% Si, 0.035% P and 0.035% Sand with 0.83mm diameter and 3.2 mm wall thickness. The fin was 16mm high and 1mm thick shown in Figure-1. The tests were conducted in accordance with the finned tube production standard [9].