Sungmo Nam

Optimized Machining Condition Selection for High-Quality Surface in High-Speed Finish Milling of Molds

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.

Reliability Prediction of Centerless Grinding Machine

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.

Measurement of the Piping Elbow Integrity Using the Fiber-Optics Technique

This paper deals with the development of a non-destructive conditioning monitoring technique for low alloy steel piping elbows. The objective is to develop a technique, which enables on-line monitoring of the flow induced wall thinning of the elbows. The technique involves use of optic interferometry sensors for the measurement of a flow-induced vibration. The special feature of this system is that it provides a non-destuctive method and enables measurement of the very small displacements caused by wall-thinning. The system configuration and the proposed methodology to be employed related to this developmental work has been discussed. The data and information collected on the vibration characteristics of the piping elbows using fiber optic accelerometers has been analyzed. The application feasibility of the proposed fiber optic interferometer in condition monitoring for nuclear power plant has also evaluated. The results obtained so far are very encouraging with respect to the measurement of wall-thinning in the piping elbows. Introduction Pressure vessels and heat exchangers such as steam generators in nuclear power plants have very sophisticated piping systems operating in a very aggressive erosion/corrosion environment of a turbulent flow with a high temperature and pressure. These adverse operating environments make a piping system very vulnerable to accelerated wear and degradation. The condition monitoring of the tube bundles in a steam generator and piping elbows in a secondary system in nuclear power plants is one of the most interesting issues for nuclear inspection and maintenance activities.[1] Several methods to measure the wall-thinning effect of a pressure tube have been developed. One is the electro-chemical approach such as a pH sensor, and an electro-chemical corrosion potential sensor.[2] But these sensors require the penetration of the pressure piping to contact the measured fluid, therefore, are not a non-destructive method. The second is the ultrasonic method, which is widely used in the nondestructive technology. Even though the ultrasonic transmitter has a good capability to measure the wall thickness of pressurized piping under a single phase fluid within the piping, it is difficult to measure the wall thickness when two phase and turbulent fluid exists in the pressurized piping.[3] The last is a passive method which is to measure the changes of the physical phenomena of the passive components such as elastic waves, and pipe or tube vibrations due to fluid flow. The measurement of vibration generally requires the determination of the displacement of a surface as a function of time. The measurement is to determine the amplitude and frequency content of the vibration. In general, measurements are not required to respond to vibrations over the range of 1 Hz to 1 MHz with amplitudes ranging from a few millimeters to a sub-angstrom. Many of the standard means of monitoring vibration utilize accelerometers, which are contact devices and have limited resonance bandwidths. If the vibrating target can be incorporated into an interferometer, this Key Engineering Materials Online: 2004-08-15 ISSN: 1662-9795, Vols. 270-273, pp 750-755 doi:10.4028/www.scientific.net/KEM.270-273.750

Neutron yield dependence on deuterium ion energy distribution from deuterated methane clusters with an intense femtosecond laser

Neutron generation experiment with deuterated methane (CD4) clusters exposed to a femtosecond laser beam (620 mJ, 28 fs) was done. The relation of ion energy distribution to cluster size was studied. By analyzing TOF ion signals, neutron yield was estimated to be 2 × 105 per laser shot.

Neutron generation induced by laser fusion by using a 10TW femtosecond Ti:Sapphire laser

A 10 TW Ti:sapphire laser is used to generate DD fusion neutrons and the characteristics of plasma has been investigated. Neutrons are generated from deuterium clusters which are formed from deuterium gas jet when cooled down to liquid nitrogen temperature.