Papers by Author: Yong Hoon Cha

Abstract: Vibrations during lathe machining include vibrations by a sudden clash of a tool against a workpiece as an external excitation, vibrations by irregular tissues of the workpiece, vibrations by regular excitation due to asymmetric torque, and vibrations by bearing defects. Furthermore, machine tools are heated because most of the supplied energy is transformed to heat and becomes the heat source of the machine tool or an internal heat source. In addition, the spindle is one of the largest internal heat sources. The heat distortion of the spindle by this heat source has the most serious effect on the total heat distortion of the machine tool, and the heat distortion of machine tools is the largest cause of the degradation of cutting precision. In order to obtain accurate data about the causes of such vibrations and heat, this study measured the vibrations and thermal changes of each specimen using a vibrometer and an infrared thermography camera.

Abstract: In this research, we used nondestructive test based on ultrasonic test as inspection method, and made up inspection robot in order to control of ultrasonic probe on the SWP surface, and programmed to signal processing code and pattern classifying code by user made programming code. For evaluation of flaw signal is reflected on welding flaw, user-made program codes are composed of signal processing and probability neural network (PNN) and backpropagation neural network (BPNN). And then, we actually confirmed to the theoretical advantage of each neural network method compared probability neural network with backpropagation neural network for classification and recognition rate. For the application of classifier to SWP inspection system, BPNN classifier is adequate in the first stage. And then, the application of PNN classifier is adequate as the next stage. Because of PNN application need enough sample data that is due to probabilistic density function.