• Journal of the Korean Society for Precision Engineering
• /
• v.19 no.3
• /
• pp.101-106
• /
• 2002

This paper presents an experimental investigation of high speed machining of dies and molds. Several critical issues involved with the high speed machining of QRO90 tool steel of hardness up to HRc62, have been studied and explained from a detail analysis of experimental observations. The experiments were performed using ball end mills. The effect of different process parameters on tool life and surface finish produced was also investigated. The cutting parameters involved were; cutting speeds in the range of 100 to 40 / m/min, axial depth of cut from 0.1 to 0.5mm, pick feed of 0.1 to 0.5mm. Run out and acceleration signals were observed during the experiment to investigate cutting slates. Compressed air and flood coolant were used and the effect of coolant on tool life was also determined.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.12 no.5
• /
• pp.1035-1042
• /
• 1988

The acoustic emission(AE) signal is monitored in milling operation in order to investigate the relationship between the progressive tool wear and the AE signals. A signal processing technique so called time domain averaging(TDA) is presented for the elimination of the influences of the noise imbedded in the periodic signals. The relationship between the progressive tool wear and the AE signals is investigated by varying the cutting speed, feed, depth of cut and the number of insert. From the measured data, it is observed that the averaged level of the AE signal increases at first with the increase of flank wear to a certain critical value, and then stays almost constant or fluctuates with further increase of the flank wear.

• International Area Studies Review
• /
• v.18 no.3
• /
• pp.231-248
• /
• 2014

The relationship between market structure and social welfare outcomes has received considerable critical attention in the field of competition policy research. In particular, it is necessary to study in greater depth the impact of market power on social welfare in the telecommunications industry, which is highly likely to form a monopolistic market structure. This is because, when market powers are concentrated on few upper carriers, there are negative effects on social welfare due to an excess of profits. Against this background, the present study investigates the relationship between the market structure of the mobile communications industry (the level of market power) and social welfare outcomes (the retail rate cut) through an international comparison. The results demonstrate that both the market structure and competition status of the Korean market have had significant gaps in global trends. It also points out that the monopolistic market structure (when the leading provider has more than 50% of the market share) has significantly negative effects on consumer welfare (the retail price cut). In addition, the findings of this study suggest that the direction of competition policy should focus on not only improving market concentration(HHI), but also on mitigating the monopoly of power of a dominant operator.

• Journal of the Korean Society for Precision Engineering
• /
• v.27 no.8
• /
• pp.62-69
• /
• 2010

Internal lathe machining with a boring bar is weak with respect to vibration because the bar is long and slender. Therefore, it is important to study the dynamic characteristics of a boring bar. The purpose of this study was to identify the effects of overhang and cutting conditions on the dynamic response characteristics of a boring bar. For an efficient experiment, an $L_g(3^3)$ orthogonal array was applied and the results were quantitatively analyzed by ANOVA. Overhang, feed per revolution, and depth of cut were selected as independent variables. Meanwhile, dynamic stiffness, damping ratio, damping coefficient, and acceleration were chosen as dependent variables. The vibration signal was obtained from an accelerometer attached to the boring bar, followed by visualization by a signal analyzer. The effect of overhang was found to have a significant effect on the dynamic stiffness, damping ratio, and damping coefficient, but the other variables did not. As the length of the overhang increased, the dynamic stiffness decreased and the damping ratio increased. In addition, the damping coefficient increased until the length of the overhang was 4D (where D is the shank diameter), after which it remained constant. The acceleration decreased until the overhang length was 4D, and then increased sharply when the overhang was increased further. From these results, the behavioral trend of the damping characteristics changed when its overhang length was 4D. Consequently, there is a critical point that the dynamic characteristics of boring bar change.