Papers by Author: Jong Do Kim

Abstract: Laser material processing is a very rapidly advancing technology for various industrial applications, because of its many advantages. A few of its major advantages, less yet better controlled heat input, have been successfully exploited for the very critical application of aluminum alloy welding. This study suggested the source of weld-defects and its solution methods in welding a lithium ion battery with pulsed Nd:YAG laser. In the experiment, battery case has changed over joint geometry from side welding to flat welding. In the case of an electrolyte inlet seal welding, welding was carried out after pressing an Al ball and the degree of eccentricity, the contact length and the gap are presented as major parameters. With the Al ball indent improvement, the eccentricity and the gap were reduced and the contact length was increased. As a result of an experiment, a sound weld bead shape and crack-free weld bead were obtained.

Abstract: In general, magnesium metal is not used as uncoated material on account of its corrosion characteristic. This work was done by preparing 99.99% pure magnesium coating films by RF magnetron sputtering onto SPCC substrates [1]. The individual preparation conditions of gas pressures and bias voltages were 1×10-2 ~ 1×10-3 Torr and 0V ~ -300V, respectively. The analysis about crystal orientation, morphology and electrochemical characteristic of Mg thin films was performed by using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), electrochemical impedance spectroscopy (EIS) etc.. It is as a results of experiment that the morphology of the sputtered films changed from a columnar structure to a granular structure when Ar gas pressure increased or bias voltage decreased. Also, the prepared Mg thin film’s morphology did not have defects and pinholes, and the corrosion resistance was improved by the formation of a homogeneous passive layer.

Abstract: Welding tasks in shipbuilding create great problems for a manual welder since welding takes place in closed area with associated work environmental problems. This paper addresses the problems involved in the welding robot with control algorithm and system. The control system may similarly be modified as a tracking simulation test. The performance of the control system is assessed through the use of field data. The aim of this paper is to determine feasible parameters for a welding procedure with simulation for seam tracking of welding robot system. The main advantage of tracking simulation is its flexibility in that as the welding parameters are modified at a sufficiently high rate. Tracking simulation showed that the development of robot control algorithms should be performed by simulation, since it saves time, expenses and efforts. This paper will contribute to an increased use of automated welding technology with tracking simulation methods. Also, this paper’s results can be used for the optimization of welding process using simulation method with LabVIEW.

Abstract: This study examines for keyhole behavior by observing the laser-induced plasma and investigates the relation between keyhole behavior and formation of weld defect. Laser-induced plasma has been accompanied with the vaporizing pressure of zinc ejecting from keyhole to surface of primer coated plate. This dynamic behavior of plasma was very unstable and it was closely related to the unstable motion of keyhole during laser welding. As a result of observing the composition of porosity, much of Zn element was found from inner surface of it. But Zn was not found from the dimple structure fractured at the weld metal. therefore we can prove that the major cause of porosity is the vaporization of primer in lap position. Mechanism of porosity-formation is that the primer vaporized from the lap position accelerates dynamic behavior of the key hole and the bubble separated from the key hole is trapped in the solidification boundary and remains as porosity.

Abstract: The application of laser welding technology has been considered to shipbuilding structure. However, when this technology is applied to primer-coated steel, good quality weld beads are not easily obtained. Because the primer-coated layer caused the spatter, humping bead and porosity which are main part of the welding defect attributed to the powerful vaporizing pressure of zinc. So we performed experiment with objectives of understanding spatter and porosity formation mechanism and producing sound weld beads in 6
t primer coated steels by a CO2 CW laser. The effects of welding parameters; defocused distance, welding speed, coated thickness and coated position; were investigated in the bead shape and penetration depth on bead and lap welding. Alternative idea was suggested to suspend the welding defect by giving a reasonable gap clearance for primer coated thickness. The zinc of primer has a boiling point that is lower than melting point of steel. Zinc vapor builds up at the interface between the two sheets and this tends to deteriorate the quality of the weld by ejecting weld material from lap position or leaving porosity. Significant effects of primer coated position were lap side rather than surface. Therefore introducing a small gap clearance in the lap position, the zinc vapor could escape through it and sound weld beads can be acquired. In conclusion, formation and suspension mechanism of the welding defects was suggested by controlling the factors.