Papers by Author: Seok Woo Lee

Abstract: In this work, machining test was carried out in various machining conditions using ultrasonical vibration capable CNC machine. For work material, alumina ceramic (Al2O3) was used while for tool material diamond electroplated grinding wheel was used. To evaluate ultrasonical vibration effect, grinding test was performed with and without ultrasonic vibration in same machining condition. In ultrasonic mode, ultrasonic vibration of 20kHz was generated by HSK 63 ultrasonic actuator. On the other hand, grinding forces were measured by KISTLER dynamometer. And an optimal sampling rate for grinding force measurement was obtained by a signal processing and frequency analysis. The surface roughness of the ceramic was also measured using stylus type surface roughness instrument and atomic force microscope (AFM). Besides, the scanning electron microscope (SEM) was used for observation of surface integrarity.

Abstract: Micro turning test was performed on nickel plated roll die using ultra precision lathe and lenticular shape single crystal diamond (SCD) tools. For the test, fresh tools were used for each experiment to observe tool wear evolution at the cutting distances. Finite element method (FEM) simulation based on Lagrangian method was also used to calculate contact stress on the cutting surface during the machining process. For the tool wear measurement, scanning electron microscope (SEM) and 3D Nano View, which can provide surface topography of the tools, were used. In addition, Kistler dynamometer was utilized for cutting force measurement. From the experimental result, it was found that a dominant wear mechanism was abrasion due to high contact stresses on the cutting tool surface. And it was also observed that high cutting speed caused high wear rate but slighlty reduced the cutting forces.

Abstract: In this work, grinding test was performed in terms of machining parameters, such as grinding speed, feed rate, etc., in order to study effect of ultrasonic vibration in grinding. The design of experiment (DOE) approach was used for an optimal condition of ultrasonic assisted grinding, which can minimize the grinding forces. In DOE, ultrasonic amplitude power, feed rate, and rotation speed of spindle were chosen as the major machining factors. The grinding forces were measured and compared between the conventional grinding and ultrasonic assisted grinding. From the experiment, it was found that the grinding forces decreased as the ultrasonic vibration power and the rotation speed of spindle increased while the grinding force was reduced as the feed rate increased. In addition, regression model was formulated for obtaining optimal grinding condition.

Abstract: In this paper, a ultrasonic horn, which can vibrate longitudinally with a frequency of 20㎑, was designed using finite element method (FEM). And the ultrasonic horn was fabricated for ultrasonic assisted grinding. To evaluate machining performance of the fabricated ultrasonic horn, grinding test was conducted on alumina ceramic (Al2O3). In the grinding test, grinding forces was measured and compared between the conventional grinding and the ultrasonic assisted grinding. The results showed that the grinding force in the ultrasonic grinding was lowered than the conventional grindign by 3~20%.

Abstract: An FE model can be usedfor better understanding the micro cutting process. To identify an edge wear effect, the cutting forces and contact stress on the cutting tool were measured as edge wear progress. On the other hand, a series of orthogonal cutting tests was also carried out forcomparisonwith FEM simulation results in termsof chip formation and cutting forces. A scanning electron microscope (SEM) was used to observe the tools and chips for the purpose of taking measurements. A Kistler dynamometer was also utilized for cutting forces measurement. The FEM micro cutting simulation showed good agreement with experimentalresults in terms of the cutting forces and chip formation. And it was observed in both FEM simulations and experiments that larger edge wear caused higher cutting forces.

Abstract: The application of an ultrasonic vibration is one of promising means in machining micro-holes. In this study, the differences of in the geometric machining mechanism between the ultrasonic and the conventional drilling were investigated. Specifically, the uncut chip thickness before machining and the tool trajectories of the cutting edges were formulated and compared with machining results. Through the machining experiments, it was found that those these parameters well matched with the appearance of both the disposed chips and the machined surface. Furthermore, the results indicated that the change of uncut chip thickness resulted in decreased machining resistance as well as improvement of the machined surface

Abstract: Today, the trend in die and mold manufacturing is to pursue high-quality surface topology using high-speed finish milling operation. This paper presents a new approach to optimize machining conditions according to the required material removal rate (MRR), focusing on obtaining a high-quality surface. In this approach, the prediction model of surface roughness using the 2-staged artificial neural network (ANN) is employed for the objective function. Furthermore, an additional surface quality criterion is also used for the optimization problem using the genetic algorithm. It has been investigated that optimized machining conditions can be selected to obtain the high-quality surface within allowable reliability while maintaining a high-quality surface, under the given desired MRR.

Abstract: FIB equipment has the ability to perform etching and chemical vapor deposition simultaneously. It is very advantageously used to fabricate micro structure components having 3D shape because it has a minimum beam size of Φ 10nm and smaller. Currently, FIB technology has been studied the research fields relating to two problems such as low accuracy and low productivity due to redeposition and a charging effect. This paper focuses on applying FIB technology to the field of micro mold fabrication and repair. As such, the simple micro pattern fabrication techniques and the experimental characteristics are studied on FIB-CVD according to ion beam condition and scanning area. We have encountered some remarks that the result of the experiments according to beam current of 8 pA, shows superior CVD yield. But the result of 1318 pA shows the pattern etched off. Furthermore, we also analyzed the scanning area effect for FIB-CVD yield and suggest the maximum yield condition of the chemical vapor deposition for micro part fabrication.

Abstract: Along with the recent developments in the optical communication industry, the demand for optical communication components has increased. Ferrule is a significant element that determines transmission efficiency and quality of information in the optical communication area. Most ferrule machining entails grinding and this requires high processing precision. Therefore, the ultra precision centerless grinding machine for ferrule grinding was designed. The centerless grinding machine is composed of a high damping bed, grinding wheel spindle unit, regulating wheel spindle unit, feeding table and dressing unit. Reliability prediction is very important for the high quality design. In this study, reliability of the centerless grinding machine was predicted.

Abstract: This paper carried out some experimentation and verification of the chemical vapor deposition induced ion beam and sputtering using the SMI8800 manufactured by SEIKO. FIB-CVD is very useful tools to repair the mask or IC with sub-micrometer precision. However it need to be much studied in some fields such as FIB-CVD mechanism and the characteristics of pattern accuracy and yield of CVD according to many parameters related to ion beam, beam scanning methods and type of specimen etc. Therefore the verification on FIB-CVD characteristic such as accuracy and yield according to scanning area and scanning time is carried out in this study. And it suggests the optimization parameters, various mechanisms of the chemical vapor deposition induced ion beam and sputtering effect for simple pattern.