Jeong-Suk Kim

Development of an on-line tool-life monitoring system using acoustic emission signals in gear shaping

Sensing techniques for monitoring machining processes have been one of the focuses of research on process automation. This paper presents the development of on-line tool-life monitoring system for gear shaping that uses acoustic emission (AE). Characteristics of the AE signals are related to the cutting condition, tool material and tool geometry in the cutting of metals. The relationship between AE signal and tool wear was investigated experimentally. Experiments were carried out on the gear shaping of SCM 420 material with a pinion cutter having 44 teeth. Root-mean-square (RMS) AE voltages increase regularly according to tool wear. It is suggested that the maximum value of RMS AE voltage is an effective parameter to monitor tool life. In this study, not only the acquisition method of AE signals for rotating objects but also the signal-processing technique were developed in order to realize the in-process monitoring system for gear shaping. The on-line tool-life monitoring system developed has been successfully applied to gear machining processes.

Tool wear measuring technique on the machine using CCD and exclusive jig

Abstract Recently the applications of high speed machining have increased due to the need for high precision and high accuracy machining and machining of difficult-to-cut material. However, the high speed machining also accompanies problems: the product quality can be degraded due to the tool wear and the product cost can be increased due to frequent tool replacements. Therefore, it is necessary to develop a technique of quantitative tool wear measurement to determine the precise timing for tool replacement. In this respect, this study suggests a reliable technique for the reduction of error components by developing a system using a CCD camera and an exclusive jig to be able to precisely measure the size of tool wear in a direct manner, in addition to partly introducing Taguchi method.

A study on the precision machinability of ball end milling by cutting speed optimization

Abstract This study proposes an optimization cutting speed program developed to improve the machining precision and tool life in high speed machining using the ball end mill. This program optimizes the cutting speed that varies during free surface machining. As for the technique of optimization cutting speed, the NC code generated from CAD/CAM goes through a reverse post process and cutting simulation and the effective tool diameter of the ball end mill is obtained. Then the range of critical cutting speed suitable for the workpiece is selected and the spindle revolution is changed according to the effective tool diameter within the range of the critical cutting speed. In this paper, the machining precision and tool life were compared in the free surface machining conducted by the general cutting method and the technique of optimization cutting speed.

Chip load prediction in ball-end milling

Abstract In the modern manufacturing of sophisticated parts with 3D sculptured surfaces such as dies and molds, ball-end milling is one of the most widely used machining processes to remove unwanted material. However, the machining processes are accompanied by cutting forces that cause tool chattering and dimensional errors. In this paper, a calculation algorithm for the chip load along the cutting edge is proposed, so that it is can be used for predicting cutting forces and the region with excessive dimensional error in the ball-end milling process. For this purpose, an exact chip engagement surface (ECES) from cutting edge geometry is suggested to be a mathematical model with the feed rate effect of cutter, instead of a semi-spherical surface. With the calculated chip load distribution, a simplified method for calculating cutting force at a cutter location is also proposed.

Right Ventricular Wall Hematoma Secondary to Percutaneous Coronary Intervention

Intramyocardial hematoma is known to be associated with myocardial infarction, chest trauma, coronary artery bypass operation, and complication of percutaneous coronary intervention (PCI). We describe here a rare case of 50-year-old man with a huge right ventricular (RV) wall hematoma which was newly developed two hours after PCI. The patient was treated conservatively with a successful outcome. We discuss plausible mechanisms for the development of RV wall hematoma and treatment options for the case.

Machining Characteristics of Micro-Flow Channels in Micro-Milling Process

□ This article presents a method for machining micro-flow channels on dies for precise and effective mass production of metallic bipolar plates of proton exchange membrane fuel cells (PEMFCs). To find an effective method for machining micro-flow channels on dies of metallic bipolar plates, machining experiments are conducted on micro-flow channels using a micro-scale milling process under various machining conditions. Machining variables are axial depth of cut, feed per tooth, supply/non-supply of cold wind, and single-tool/multi-tool cutting processes. The machining process is monitored by acquiring cutting force signals and acoustic emission signals while conducting the experiments. Surface conditions of machined micro-flow channels are analyzed. In this study, a cold-wind process is better than other processes in terms of burr generation and surface roughness. A cold-wind process with multi-tool process has a particularly better surface quality than the other processes.

Lab on a fabric: Mass producible and low-cost fabric filters for the high-throughput viable isolation of circulating tumor cells

Circulating tumor cells (CTCs) play an important role in estimating the presence and the metastatic relapse of tumor. Despite of their importance, isolation of viable CTCs is still struggling, since chemical or mechanical damages are unavoidable when separating less than 1000 of CTCs out of billions of other blood components. Furthermore, the current CTC isolation devices show low productivity, since they are produced after a series of complicated fabrication processes. Here, we present a low-cost and mass-producible fabric filters for the viable CTC isolation and the further molecular assay for profiling cancer-associated markers. The fabric filter, produced by polyester monofilament yarns, can be massively produced at extremely low-cost, by showing productivity of ~22filters/s at ~59filters/USD. By utilizing size-based sorting method, the fabric filter is capable to isolate both epithelial and mesenchymal CTCs, while slots with curved walls are beneficial for preventing the cell rupture by reducing 21.6% of mechanical stress compared to the conventional straight-walled slots. We applied our filter to 11 human blood samples and found that the number of CTCs was closely related to the expression level of Ki-67, which is highly overexpressed in proliferative tumors. The fabric filter might be an appropriate caner-screening tool in developing countries, where people suffer from insufficient healthcare services.

Point of tool change time and monitoring program for microscale milling process

In this article, a point in time at which tool change should take place and a program to monitor tool condition are proposed for microscale milling processes. The response surface method, which is one of designs of experiments, was used to determine cutting conditions. The independent variables were the spindle speed, axial depth of cut, and feed per tooth; each variable was divided into five levels. After tool life measurement experiments were performed with the determined cutting conditions, a second-order tool life equation was derived, and optimal cutting conditions were obtained by means of the tool life equation. A point of tool change time for the microscale milling process was proposed by analyzing the characteristics of cutting force signals and acoustic emission signals acquired during the experiments. Then the values were determined by analyzing the experimental results and were used to determine the tool change time in a machining monitoring program. The results of this study may be used to enhance machining efficiency in microscale milling processes.

Analysis on the correlation between cutting signals and surface quality in milling process of Ti-6Al-4V

The application of Titanium alloys has gradually increased because of its superior thermal and mechanical properties. Ti-alloys have higher strength and light weight compared to steel. However, Ti-alloys have poor machineability due to their low thermal conductivity and stiffness. As the machining proceeds, the tool wear is accelerated and abnormal conditions such as chipping and fracture of cutting edge occur. This paper presents an investigation on the effect of tool wear on surface quality in milling process of Ti-6Al-4V. The cutting force signals and acceleration signals are acquired during the machining experiments. And the machined surface is observed to check tool marks and surface roughness. The experiments are conducted until the milling tool is completely worn out. The changes of cutting force, acceleration, and surface condition according to tool wear are analyzed in machining process.

Investigation on the correlation between micro burrs and AE signal characteristics in micro-scale milling process

Micro burrs are likely to occur due to the size effect associated with cutting edge radius in a micro-scale milling process. Micro burrs reduce the machined surface quality and cause damages to the contact surfaces of micro parts, so it should be removed through the deburring process. However, the micro burrs formed by micro cutting process are not easy to remove, and require much time and cost for deburring process. Therefore, it is necessary to suppress the generation of micro burrs by the optimization of machining process. Also, it is important to detect the generation of micro burrs in advance through real-time monitoring of cutting signals to change in cutting conditions. In this paper, the influence of each cutting variables on the size of micro burrs and the correlation between micro-burrs and cutting signals are investigated through micro channel machining experiments in micro-scale milling process. The feed per tooth and spindle speed in the cutting variables are selected as independent variables. Each variable is divided into 3 levels and a total of 9 cutting conditions are derived. The size of micro burrs formed on the micro-channels is measured, and the effect of each cutting variable on the generation of micro burrs. Also signal characteristics such as AE RMS, band energy, AE count are extracted through signal processing of AE signals and the correlation between the size of micro burrs and the AE signal characteristics is figured out.