Papers by Author: Jeong Hoon Ko

Abstract: Structural SiC (α-type) is believed to be widely applied in hostile environments such as high-temperature, high-corrosive applications in the semiconductor industries due to its superior thermo-physical and mechanical properties. However, the extremely high hardness and brittleness of SiC makes hole drilling difficult by the conventional mechanical drilling (CMD) technique. Laser can be used to drill SiC; but the resultant holes are often tapered and uneven, with tendency for microcracks and thermal damage to occur at the hole entry due to the high thermal shock from the laser. This paper reports on the experimental results of a sequential laser-mechanical drilling (LMD) technique for drilling α-SiC. At first, an Nd:YAG laser was used to drill a series of pilot holes on a 3 mm thick SiC plate. Then a diamond-coated carbide drill was sequentially applied to these holes to obtain desired hole diameter of 0.5 mm. A number of through holes on SiC (aspect ratio: 6) were successfully obtained using this approach. The quality of the drilled holes were assessed in terms of the entrance and exit sizes and conditions, hole taper angle, hole edge shapes, and microcracks. Finally, comparisons of the LMD performances were also made against the holes predrilled by the laser itself and holes of the similar size drilled separately with the CMD technique. The experiment results show that the proposed drilling approach can effectively drill α-SiC ceramics.

Abstract: One-directional ultrasonic vibration assisted milling system is designed and its performance is investigated in terms of machined surface quality under 135,000 rpm. The ultrasonic vibration generator excites the workpiece with a frequency around 40 kHz and amplitude of a few micro meters. The milling tool’s cutting speed is controlled by an air-bearing spindle system. Both feed-directional and cross-feed directional ultrasonic vibration assistance are considered in order to understand the mechanism of ultrasonic vibration assistance for surface roughness generation. A comparison is done on a milled surface which is generated with and without ultrasonic vibration assistance. The experimental results show that ultrasonic vibration assistance can improve the machined surface quality which depended on the cutting edge radius and the feed per tooth.