Since metal transfer in the gas metal arc welding (GMAW) has a significant effect on weld quality, investigation has been carried out extensively to analyze the mechanism of metal transfer. Recently, the pulsed GMAW process has been utilized to improve weld quality by controlling metal transfer through detaching a droplet per current pulse. In this work, mechanical vibration of welding wire is employed to detach the molten droplet in a controlled way. Analytic modeling and experiments are conducted to investigate the dynamic effects of the vibrating electrode on drop detachment in GMAW.
In order to achieve this goal, a dynamic force balance model (DFBM) is proposed as an extension of the previous static force balance model to simulate the metal transfer in arc welding. Dynamics of the pendant drop is modeled as the second order system, which consists of mass, spring and damper. The spring constant of a spherical drop at equilibrium is derived in the closed-form equation, and the inertia force caused by drop vibration is included in the drop detaching condition. Based on the proposed DFBM, simulation of the vibrating electrode is performed numerically, and effects of the GMAW system including the power source, wire melting and welding arc on metal transfer are analyzed. Experiments were performed under various welding conditions using a simple apparatus including the goose-neck torch and motor, which vibrates the torch sinusoidally in the axial direction. Simulated and experimental results are compared to verify the proposed model and effectiveness of vibrating electrode system.
The simulation results show the small inertia force in the low current range. With current increase, the inertia force grows larger than the gravitational force and reaches half of the electromagnetic force at the transition current, which demonstrates considerable effects on drop detachment at the high current. The proposed dynamic force balance model predicts the detaching drop size more accurately than the previous static force balance model. The dynamic behavior of the GMAW system under mechanical vibration is also simulated using a dynamic force balance model for free-flight transfer mode and short-circuit transfer model, and these are incorporated with the characteristic equations for the power supply, wire and arc. The behavior of the GMAW system is described more precisely and variation of welding parameters are simulated continuously during short-circuit as well as free-flight transfer modes. The calculated results are in broad agreements with the experimental results for argon shielding. While some improvements of weld quality are observed using the vibrating electrode system under limited welding condition, it may not be acceptable to be utilized in practice considering the degree of improvements and complexity in the vibrating device.
