Control of wire transfer behaviors in hot wire laser welding

Abstract

Hot wire laser welding reduces the requirement of wire feeding accuracy and improves wire deposition efficiency with preheating wire by resistance heat. Due to merits like low heat input and high deposition rate, this method has broad potential applications like welding and additive manufacturing. It is a key problem to maintain stable wire transfer in hot wire laser welding since the preheated wire should be kept contacted with the work piece to maintain high temperature. A high-speed imaging system was used to observe wire transfer behaviors, which are divided into three types: fusing transfer, continuous transfer, and wire hit transfer. Only the continuous transfer is the stable wire transfer, which guarantees good weld formation. The wire transfer behavior is determined by wire temperature, and the temperature criterion of wire transfer is obtained by image analysis and temperature measurement. Two characteristic points P1 and P2 on the filler wire were found out, whose temperatures were used to judge wire transfer behaviors. The temperature criterion of the stable wire transfer is interpreted that the temperature of P1 (T _P1) must be no more than the wire solidus and the temperature of P2 (T _P2) must be no less than the wire liquidus. A heat conduction model of hot wire laser welding was established to calculate T _P1 and T _P2 for the used 308-L stainless wire. The welding parameters, which made up isothermal surfaces of T _P1 = 1398 °C and T _P2 = 1454 °C, respectively, the solidus and liquidus of the used wire, were obtained by iteration calculation of wire temperature. The parameters window of the stable wire transfer was located between the two isothermal surfaces. For the stable wire transfer in hot wire laser welding, the resistance heat of the wire cannot exceed the heat which fuses the wire tip outside the molten pool. Meanwhile, the total heat of the wire, including the resistance heat and the heat conducted from the molten pool, must exceed the heat which melts the wire tip inside the molten pool.