Eligible CO2 content in Ar-CO2 mixture shielding gas for improving metal transfer in metal-cored arc welding
Ngoc Quang Trinh, Shinichi Tashiro, Khoi Dang Le, Tetsuo Suga, Tomonori Kakizaki, Kei Yamazaki, Ackadech Lersvanichkool, Anthony B. Murphy, Hanh Van Bui, Manabu Tanaka
Abstract
• This study presents a quantitative measurement of the metal transfer frequency of a metal-cored wire under various argon-CO2 shielding gas mixtures (5, 10, 15, 20, 25,50, and 100%) and compares it with that of a solid wire. • Through shadowgraph observation and arc plasma investigation, the mechanism of the effect of CO2 concentration on the metal transfer of the metal-cored wire was proposed. • The metal transfer frequency of solid wire was monotonically decreased when CO 2 content increased, while that of the metal-cored wire reached a peak at a critical CO 2 concentration of 15%. • The equilibrium between arc attachment and the length of unmelted flux at the wire tip was found to influence droplet detachment behavior. Both factors were notably influenced by the CO 2 content, with equilibrium being attained at a CO 2 concentration of 15%. Metal transfer frequencies in a gas metal arc welding process with a metal-cored wire were quantitatively measured for the first time as a function of the CO 2 content (i.e., 5, 10, 15, 20, 25, 50, and 100%) in argon-CO 2 shielding gas mixtures at welding currents of 220, 250, and 280 A, and the results were compared with those of a solid wire. As a result, the metal transfer frequency of solid wire was monotonically decreased with the CO 2 content owing to an increase in the arc pressure, which prevented droplet detachment. However, the metal transfer frequency of the metal-cored wire presented a maximum value at 15% CO 2 under all the current levels. The transfer behavior was supposed to depend on the relation between the arc attachment position and the tip of the unmelted flux position inside the cored wire. When the CO 2 concentration was low, the arc was attached higher than the unmelted flux, causing the electromagnetic force to be ineffective in droplet separation. When the CO 2 concentration increased slightly, the arc was moved downward to the tip of the unmelted flux. That tendency temporarily facilitated the neck formation at the wire tip due to enhanced electromagnetic force flowing through the molten metal on the wire tip. Nevertheless, when the CO 2 content increased over a critical value, the arc pressure became a dominant factor to hinder the droplet detachment, which caused a decrease in transfer frequency. Consequently, the metal transfer frequency of metal-cored wire became maximum at 15% CO 2 .