Dong Sam Park

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.

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.

Characteristics of Micro-Precision Machining of Glasses by Powder Blasting

Powder blasting is similar to sand blasting and effectively removes hard and brittle materials. With an increase in the need for machining of ceramics, semiconductors, electronic devices and LCDs, micro abrasive jet machining has become a useful technique for micro-machining. In this study, we first investigated the effects of the blasted glass surface’s characteristics and shape under different blasting parameters; second, we examined the predictive models for material removal and surface roughness that have been developed in terms of blasting pressure, scanning speed and abrasive flow, using response surface methodology by experimental data. The established equation shows that the blasting pressure was the main factor influencing the material removal and surface roughness. In addition, analysis of variance for the firstorder model of material removal and surface roughness shows that the coefficient of determination (R2) is 99% and 98%, respectively. The associated p-value for the two models was lower than 0.01, indicating that the models are statistically significant.

Machining Characteristics of AlN-hBN Composites in End-Milling and Precision Lapping Processes

In this study, the machining characteristics of developed AlN-hBN composites were investigated in the end-milling and precision lapping processes. To achieve the objectives, material properties of the developed AlN-hBN composites were evaluated according to the variation of hBN contents. And, required experimental works were performed to investigate the machining characteristics of the composites. First, the machiniability of the composite was evaluated in the end-milling process under various cutting conditions, such as spindle speed, feederate, and depth of cut variations. Also, generated micro cracks caused by the cutting process were investigated via SEM photographs. Next, precision lapping experiments were performed under various conditions, and the results were estimated.

Micro Pattern Making Method on AlN-hBN Composites Using Powder Blasting Process

In this study, micro patterns were formed on the developed AlN-hBN composites using powder blasting techniques, which have been considered as one of the most appropriate micro machining methods for hard and brittle materials such as ceramics. To achieve the objective, first, material properties of the developed AlN-hBN composites were evaluated according to the variation of h-BN contents. And, a series of required experiments were performed, and the results were analyzed. As the results, it was investigated that the machiniability of the developed AlN-hBN composites increased with the increase of the h-BN contents in the composites. From the experimental results, it was possible to determine optimum blasting conditions for micro pattern making on the developed AlN-hBN composites.

Micro Groove Machining Characteristics of Si3N4-hBN Composites

In this study, the analysis of micro groove machining characteristics of Si3N4-hBN composites are performed to determine optimum micro machining conditions for related applications. As a first step, material properties of the Si3N4-hBN composites are investigated. Then, a set of micro groove machining experiments are performed to investigate the micro groove machining characteristics with variable h-BN contents and different conditions. From the results, it can be investigated that the cutting forces decrease with the increase of h-BN contents. It can be concluded that the results of this study can be applied for the micro parts production using Si3N4-hBN composites.

Micro Groove Forming on AlN/hBN Composites Using Powder Blasting Process

In this study, powder blasting techniques are applied for micro groove forming on the developed AlN/hBN composites. First, material properties of the composites are evaluated according to the variation of h-BN contents. And, a series of required experimental works are performed to determine optimum powder blasting conditions for micro groove forming. The experiments are performed for the prepared samples with masked patterns. As the results, it can be observed that the machiniability of the developed AlN/hBN composites increases as h-BN contents in the composites. Also, from the experimental results, it is possible to determine the optimum blasting conditions for micro groove forming on the developed AlN/hBN composites.