Yoon-Gyo Jung

A Continuous Control of Cutter Posture Change for Efficient 5-Axis Machining of Impeller

In 5-Axis Machining of impellers, interference problems with tool and neighboring surfaces often take place due to the narrow and deep gap between blades, so the problem of avoiding interference is very important. Also, because the efficiency of turbo machines can be maximized only when fluids smoothly flow due to the characteristics of the impeller, high quality of the machined surface is required. During 5-Axis machining of these impellers, the excessive local interference avoidance, necessary to avoid interference, leads to inconsistency of cutter posture, low quality of machined surface and increase of processing time. Therefore, in order to increase the efficiency of 5-Axis Machining of impellers, it is necessary to minimize the cutter posture changes and create a continuous tool path while avoiding interference. This study, by using an MC-space algorithm for interference avoidance and an MB-spline algorithm for continuous control, is intended to create a 5-Axis machining tool path with excellent surface quality and economic feasibility; finally, this study will verify the effectiveness of the suggested method through verification processing.

Simple monitoring of welding spatter for quantification and observation using a mobile phone

Unstable welding arcs can cause the scattering of molten welding pools, a phenomenon known as welding spatter. Spatter deteriorates product quality and necessitates inefficient secondary processes and their associated costs for its removal. Image processing studies aiming to reduce spatter have been performed, but little effort has been devoted to studying the behavior of and quantifying spatter. Furthermore, most studies use a high-speed camera to obtain welding spatter images; however, expensive high-speed cameras are not suited to practical industrial uses. In this study, the distribution of metal inert gas welding spatters is quantified and obtained using a mobile phone camera. LabVIEW vision modules are used to establish welding spatter monitoring algorithms. The mobile phone camera is installed vertically and horizontally. Sequential images are obtained to analyze welding spatter color and shape data. Vertical welding spatter images are converted to gray scale and the color range is analyzed. Welding spatter shape is extracted through the conversion to grayscale images, and welding spatter distribution is secured by tracking welding spatter shape. With this technique, spatter can be used as an index for exterior quality. Furthermore, these results can be used to measure and reduce fundamental spatter in automated welding lines.

Vibration control for a flexible rotor with a prediction control technique

This paper introduces the rotor dynamic characteristics of the multitask machine supported by magnetic bearings. This paper proposes a simulation method for vibration control of a rotor system using a finite element method and a dynamics program. This paper focuses on the applications of the prediction control technique (PCT) algorithm to vibration control of a rotor system. This thesis proposes a new simulation model method for magnetic bearing-rotor systems with a dynamic rotor system model using a multi-body dynamic analysis tool and with a PCT as a system control algorithm. The advantages of a dynamic model are the following. 1) It enables more accurate behavior observation than previous modeling methods. 2) The computing time of control simulation can be reduced. The PCT is a new control algorithm for a rotor system which can control the system using an adaptive proportional gain and an adaptive phase, which are obtained from periodical input signal. The simulation and experimental results show that the PCT is possible to control.

The Determination of Efficient Super Finishing Conditions for the Mirror Surface Finishing of Titanium

Recently, the demands for superfinishing machines have increased, but the development of superfinishing devices and superfinishing technology remain insufficient. And titanium, with its infinite potential, is widely known as a highly ideal material. It is therefore used in various industries that require precision-machined parts, such as the automobile, chemistry and aerospace industries, due to its outstanding specific strength and corrosion resistance compared to any other alloys. In this study, a series of experiments was performed to determine the mirror surface finishing conditions of titanium as well as efficient superfinishing conditions that can be utilized practically and economically at production sites. The applied conditions were the workpiece rotation speed, the oscillation speed, the contact pressure, the roller hardness and the type of abrasive film used when superfinishing was performed using an abrasive film for titanium-based materials such as pure titanium and titanium alloy. From the experiments, it was confirmed that efficient superfinishing conditions and mirror surface finishing conditions were determined for pure titanium and titanium alloy.