고출력 CW Nd:YAG 레이저를 이용한 Inconel 718 박판의 절단특성 분석 및 3차원 유한요소 해석에 관한 연구

Abstract

ABSTRACT

Investigation into the characteristics and finite element analysis of laser cutting process for CSP 1N sheet using high power CW Nd:YAG laser

Byun, Kyung-Won Advisor : Prof. Ahn, Dong-Gyu, Ph. D. Dept. of Mechanical Engineering Graduate School of Chosun University

Inconel sheets have been widely applied to industrial area, including a shipbuilding industry, the energy industry, a defense industry and other, to enhance corrosion and heat resistances of parts. Recently, in order to manufacture rapidly a part with a complex shape using a thin sheet of Inconel, several research works on laser cutting of the Inconel sheet have been actively in progress. The objective of this research work is to investigate into laser cutting characteristics of the Inconel 718 sheet with thickness less than 2 mm when CW Nd:YAG laser with a high power is utilized as the cutting heat source. In order to examine the influence of process parameters, such as the power of the laser, the travel speed of the laser and the thickness of the workpiece, on a practical cutting region, the kerfwidth, the surface roughness of the cut section, and the formation of the cut section, several linear cutting tests have been performed. Through preliminary linear cutting tests, practical cutting regions for each thickness of workpiece have been obtained. From the results of the linear cutting tests, the effects of the process parameters on the kerfwidth and characteristics of the cut section, including the surface roughness, the formation of the striation, the cut and break ratio and microstructures, have been quantitatively evaluated. Angular and loop cutting tests have been performed to examine the effect of the corner angle and the size of loop on the formation of the sharp corner. From the results of the angular cutting tests, the influence of the corner angle on the melted area of the sharp corner and the quality of the cut section in the vicinity of the sharp corner has been quantitatively investigated. From the results of the loop cutting tests, a proper size of the loop with a minimum melted area for each combination of process parameters has been estimated. Three dimensional heat transfer analysis has been carried out to investigate into the effects of the process parameters on characteristics of the heat transfer in the workpiece using a commercial code SYSWELD V9.0. The laser cutting process has been assumed as a quasi-stationary and the steady state process. The laser has been assumed as a three dimensional volumetric heat source with Gaussian distributions in a longitudinal plane of the laser and the linear variation of the Gaussian distribution. From the comparison of the results of the experiments and those of the FE analyses, proper models of the FE analyses have been obtained. In addition, the influence of the process parameters on the temperature distribution and characteristics of the heat transfer during the cutting of the workpiece has been quantitatively examined. Based on the above results, optimum cutting conditions and a proper cutting path of Inconel 718 sheets could be obtained when the Nd:YAG laser with a high power is utilized as cutting tools.