Papers by Author: Young Tae Yoo

Abstract: The objective of the present paper is to examine the effects of process parameters, such as laser power, cutting speed of the laser and thickness of the workpiece, on characteristics of the cut section in the cutting of cold rolled steel sheets using a high-power Nd:YAG laser with a continuous wave (CW). From the results of the experiments, the influence of the process parameters on surface roughness and average striation angle has been quantitatively investigated. In addition, critical cutting speeds with a minimum surface roughness and a maximum average striation angle has been obtained. Finally, the optimum cutting conditions for each workpiece thickness have been estimated to improve both the quality of the cut section and the cutting efficiency.

Abstract: Laser welding process is widely used in the industrial field due to its numerous advantages: a small heat affected zone(HAZ), deep penetration, high welding speed, ease of automation, single-pass thick section capability, enhanced design flexibility, and small distortion after welding. In this paper, the laser weldability of Austenite stainless steel and INCONEL600 at dissimilar metal welds using a continuous wave Nd:YAG laser are experimentally investigated. INCONEL600 is being used in a steam generator tubing of pressurized water reactor(PWR) exposed to some corrosion. Therefore stress corrosion cracking can occur on this material. A research work is conducted to determine effects of welding parameters, on eliminating or reducing the extent welding zone formation at dissimilar metal welds and to optimize those parameters that have the most influence parameters such as focus length, laser power and welding speed were tested.

Abstract: Laser welding process is widely used in the industrial area due to its less affects to base metal than general welding. Laser welding has characteristics that highly affect ratio, deeply penetration depth and small heat affected zone(HAZ) due to its in a short time melting and then solidification by a high energy absorption rate. The objective of this research work is to investigate the optimum conditions of a cold rolled carbon steel(SCP1) in a laser welding process using a Nd:YAG laser with a continuous wave(CW). The determination of optimum conditions were performed to change the laser power, beam speed, focus length and then carry out an butt welding. From the results of the investigation, it has been shown that the optimal welding condition without defects in the vicinity of the welded area and with a good welding quality is 1325W of the laser power, 1.4m/min of laser welding speed and 0mm of focus position.

Abstract: Dissimilar metal welding (DMW) are used widely in various industrial applications due to the practical importance from the technical and economic aspect. However, DMW have several fabricative and metallurgical drawbacks that can often lead to in-service failures. For example, the most pronounced fabrication faults are hot cracks. Recently, DMW have used the several of heat source to decrease such as faults. Laser welding process has, in recent years, attracted more attention due to its special features: a small heat-affected zone and narrow weld bead due to the low heat input; welding at high speed; welding can be carried out in areas of difficult access; contactless energy transfer; welding in an exact and reproducible manner; possibilities for automation and robotization, and welding performed in various atmospheres. In this paper, the weldability on dissimilar metal welding of austenite stainless steel and carbon steel using Nd:YAG laser with a continuous wave was experimentally investigated.

Abstract: The purpose of this research is stability estimation of plant structure through classification and recognition about welding flaw in SWP(Spiral Welding Pipe). And, In this research, we used nondestructive test based on ultrasonic test as inspection method, and made up inspection robot in order to control of ultrasonic probe on the SWP surface, and programmed to signal processing code and pattern classifying code by user made programming code. Inspection robot is simply constructed as 2-axes because of welding bead with fixed pitch. So, inspection of welding part can be possible as composition of inspection part for tracking on welding line. For evaluation of flaw signal is reflected on welding flaw, user-made program codes are composed of signal processing and Bayesian classifier and perceptron neural network and back-propagation neural network. And then, we confirmed to superiority of neural network method compared with Bayesian classifier for classification and recognition rate. According to this result, we selected back-propagation neural network as classification and recognition method about the system of SWP stability Estimation[2]. Through this process, we proved efficiency on the system of SWP stability Estimation, and constructed on the base of the system of SWP stability Estimation for the application in industrial fields.