Eun Sang Lee

Development of a Micro Machining Technology for Fabrication of Micro Parts

Recently, ultra-precision machining and MEMS technology have taken an increasingly important position in machining of micro parts, such as PDP and IT components, as the application field of micro parts is extended. The micro machining center is effective for the fabrication of micro parts because of its benefits of low power consumption, high precision, and low machining cost. Therefore, we studied the possibility of its application to micro machining and analyzed the machining characteristics of micromachining. Furthermore, in this paper the application technology on micro parts is reported.

Microstructure and Mechanical Properties of Silicon Nitride/h-BN Based Machinable Ceramics

The effects of h-BN content on the microstructure, mechanical properties, and machinability of Si3N4 ceramics were investigated. The relative density of the sintered compact decreased with increasing BN content. The flexural strength also decreased with h-BN content, mainly due to lower Young’s modulus of h-BN compared to Si3N4. With increasing h-BN content, Si3N4/h-BN based ceramic composites revealed enhanced crack resistance (R-curve) behavior. The Vickers indentation crack paths in specimens are sinusoidal due to bridging and pull out of grains during crack propagation. The grain size of ß-Si3N4 slightly decreased with h-BN content. During milling and micro-drilling process, monolithic Si3N4 ceramic could not be machined, due to brittle fracture. However, thrust forces measured for Si3N4/h-BN composites decreased with increasing h-BN content, showing the excellent macro and micro machinabilty.

Machinability in Precision Grinding of Aspheric Optical Lens with Diamond Wheel

In order to do the precision grinding of optical aspheric lens, it is essential to achieve high quality surface roughness. Experiments show that the contacting area between the wheel and workpiece in a grinding process is critical to influence the surface roughness for a fine grit size resin bonded wheel. The precision grinding are performed with BK7 optical lens. This paper deals with the grinding of an aspheric surface optical lens by diamond wheel. This study also compares each machining parameter (work spindle speed, wheel spindle speed, feedrate, etc.) in rough grinding, fine grinding and polishing on the aspheric lens. In this study, several experiments were carried out BK7 optical glass lens by using vitrified, metal, resin bond diamond wheel and the polisher of urethane ball was used to remove the tool marks with an ultra-precision in-line grinding system. It was found that machining parameters significantly influence the surface roughness of aspheric optical lens.

Microstructure and Mechanical Properties of AlN-BN Based Machinable Ceramics

AlN based machinable ceramics with h-BN contents in the range of 5 to 30 vol% were prepared by hot-pressing at 1800°C for 2 h, using 3 wt% Y2O3 as sintering aids. The effects of hBN content on microstructure, mechanical properties, and machinability were investigated. The relative density of sintered compact decreased with increasing h-BN content. The four-point flexural strength also decreased with increasing h-BN content, mainly due to the much lower Youngs modulus of BN compared to AlN. In addition, the residual tensile stress, formed by the thermal expansion coefficient difference between AlN and h-BN, might cause the drop of the strength. The h-BN particles had the desired crack deflection increasing effect. However, the fracture toughness decreased with h-BN content. During end-milling process, feed and thrust forces measured for all kinds of specimens decreased with increasing h-BN particles. From the experimental works, excellent machinability of the composites was investigated, and good surface roughness of specimens is observed after machining process. Also, irrespective of h-BN content, relatively good surfaces with roughness less than 0.5 μm (Ra) could be achieved within short lapping time. Introduction Aluminum nitride (AlN) is an excellent candidate for use as substrates in electronic packaging and electrical, optical material field because of high thermal conductivity, high translucent properties and thermal expansion coefficient close to that of silicon (Si) [1]. It is need to precision machining in order to expand those applications for precision parts. However, high resistance force of cutting and difficulty of machining due to brittle fracture behavior of ceramics makes it a difficulty for manufacture as complicated shapes in various products. Though it is possible to machining by diamond abrasive [2] and cutting by laser tool [3], it has a limitation to manufacture complicated shapes and a problem of price [4]. AlN-BN based ceramics can be machined easily since cleavage plane of h-BN can facilitate crack propagation during machining, thereby decreasing cutting resistance [5,6]. The purpose of this study is to optimize machinability of AlN-BN composite by investigating the effect of h-BN content on microstructure, mechanical properties, and machinability. Experimental Procedure In this experiment, AlN (2.9 μm, Tokuyama) and h-BN (2.6 μm, T.D.K) in range from 0 to 30 vol% was used. As sintering aids, 3 wt% of Y2O3 (<0.5 μm, Shinestu Chemical Co.) were added. The powder mixture was prepared by wet ball milling in ethanol for 72 h in alumina pot. After mixing, Key Engineering Materials Online: 2004-05-15 ISSN: 1662-9795, Vols. 264-268, pp 873-876 doi:10.4028/www.scientific.net/KEM.264-268.873

A Study on the Optimum Condition Selection of Rotary Dressing System of Ultra-Precision Centerless Grinding Machine for Ferrule

The optimum condition selection of rotary dressing operations using Hall and AE sensor is presented. The acquired current signals from a hall sensor were studied as one of the method to obtain the optimum condition of dressing and the correlations between dressing condition and AE signals were also evaluated with the root mean square (RMS). Dressing operation was performed to investigate the effects of depth of cut, rotating speed and coolant. In order to verify the optimum condition of dressing, AE and hall sensor signals were compared in RMS with the surface micrograph of grinding wheel. This verification experiment demonstrates the effective dressing condition selection for centerless grinding.

Application of Powder Blasting Techniques to Micro-Pattern Making Process for Si3N4-hBN Composites

In this study, micro powder blasting techniques are applied to micro-pattern making process using developed Si3N4-hBN composites. Material properties of the developed machinable ceramics according to the variation of h-BN contents, those are used to give good machinability to the ceramics, are evaluated. And, a series of required experimental works are performed to determine optimum powder blasting conditions for micro-pattern making. The experiments are performed for the prepared samples with no mask, and samples with three different mask patterns. As the results, it can be observed that the machinability of the developed Si3N4-hBN composites increases as the h-BN contents in the composites. Also, from the experimental results, it is possible to determine the optimum blasting conditions for micro-pattern making process with Si3N4-hBN composites.

Machinability Evaluation of Si3N4-hBN Composites for Micro Pattern Making Processes

In this study, machinablilty evaluation of Si3N4-hBN composites is performed for micro pattern making processes. First, R-curve behavior of Si3N4-hBN composites is investigated to understand its machinability. And, micro-powder blasting and micro-drilling processes are performed for the machinability evaluation of the composites. In the micro-powder blasting process, the machining effects on the erosion depth of samples using three different mask patterns are analyzed by varying the nozzle scanning times and compositions of h-BN. Also, in the micro-drilling process, small holes are drilled using micro-drilling machine under variable conditions. Finally, machinablity of Si3N4-hBN composites is investigated based on the obtained data. Introduction Si3N4 composites are very difficult-to-cut materials because of its high strength and hardness. Their machining mechanism can be characterized by cracking and brittle fracture due to relatively high strength and temperature resistance. However, the Si3N4-hBN composites are well known as one of the machinable ceramics, which can be easily machined with hard-alloy cutting tools. Si3N4-hBN composite materials have been used as special refractory nozzles, tubes, break rings for the continuous casting of steel, etc, owing to their high temperature resistance with chemical inertness and thermal shock resistance. Also, recently, development of special purpose parts, such as parts for semiconductor processing, parts and sensors for micro-machine fabrication, etc., has been expanded. Thus, it is essential to develop micro-machining technologies for hard and brittle materials such as glass, ceramics, etc. In this study, machinability of the Si3N4-hBN composites is evaluated for micro-pattern making processes. As a first step, R-curve behaviors of the composites are analyzed to predict the machinability. And, micro-powder blasting and micro-drilling processes are performed for the machinability evaluation of the Si3N4-hBN composites in real situation. In the micro-powder blasting process, the machining effects on the erosion depth of samples with three different mask patterns are analyzed by varying the nozzle scanning times and contents of h-BN. Also, in the micro-drilling process, small holes are drilled using micro-drilling machine under variable conditions. Finally, the machinablity of the Si3N4-hBN composites is investigated based on the obtained data. R-curve behavior analysis for machinability evaluation The Si3N4 powder used in this study is highly pure except the oxygen content of 0.8 wt% and has an average particle size of 0.17 μm, and the BN has a hexagonal crystal phase. The h-BN content in Si3N4 is varied from 0 to 30 vol%. They are hot-pressed at 1800°C for 2 hours in a nitrogen Key Engineering Materials Online: 2004-05-15 ISSN: 1662-9795, Vols. 264-268, pp 869-872 doi:10.4028/www.scientific.net/KEM.264-268.869

A Study on the Characteristics of Micro Electropolishing for Stainless Steel

Electropolishing, the anodic dissolution process without contact with tools, is a surface Treatment method to make a surface planarization using an electrochemical reaction with low current density. Stainless steel can be put various applications which require purity and high precision surface of products. The aim of this study is to investigate the characteristic of electropolishing effect for stainless steel workpieces. In order to analyze the characteristics of electropolishing effect, surface roughness and micro-burr size were measured in terms of machining conditions such as current density, machining time and electrode gap. The tendencies about improvement of surface roughness by electropolishing for stainless steel workpieces were determined.

Micro Electrochemical Polishing of TiNi Alloy for Medical Stent

The medical stent is using widely for a surgical operation, because it can reduce the pain of cardiac. When it was developed initially, medical stent was made of stainless steel, however, the TiNi alloy is widely using presently instead of stainless steel. Because, TiNi alloy has not only super elasticity and Smart Material Effect (SME) but also excellent organism compatibility. For these reason, the TiNi alloy is currently highlighted for medical stent material better than other materials. Nevertheless, this TiNi alloy is not suitable to traditional machining process. When the traditional machining process is conducted to the TiNi alloy, it cannot be discharged the machining heat and inner stress. Also, traditional machining process makes a lot of microscopic burrs on the TiNi alloy surface. This microscopic burrs and the rough surface makes injury on vascular, so, it should be necessary non-traditional machining process without defect of traditional machining. In this paper, microscopic burrs on TiNi alloy for medical stent are removed, and surface roughness of the medical stent is evaluated by Electrochemical Polishing (EP) which is one of the non-traditional machining.

An Experimental Investigation of Optimal Grinding Condition for Aspheric Surface Lens Using Full Factorial Design

To enhance the precision and productivity of ultra precision aspheric surface micro lens, the development of ultra-precision grinding system and process for the aspheric surface micro lens are described. In this paper, an ultra-precision grinding system for manufacturing the aspheric surface micro lens was developed by considering the factors affecting the grinding surface roughness and profile accuracy. This paper deals with the mirror grinding of an aspheric surface micro lens by resin bonded diamond wheel and with the spherical lens of BK7. The optimization of grinding conditions with respect to ground surface roughness and profiles accuracy is investigated by design of experiments.