• 한국공작기계학회논문집
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• 제15권5호
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• pp.79-84
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• 2006

In modem manufacturing, many products that have geometrically complicated features, including three-dimensional sculptured surfaces, are designed and produced. In the production of these complex-shaped mechanical components, e.g. automobile dies, molds, and various engineering applications, the ball-end milling process is one of the most widely used NC machining processes that consists of roughing, semi-finishing and finishing. In semi-finishing, cusps remained after roughing according to the used tools that have two patterns of stairs and wave shapes. These cusp shapes have air-cut in cutting and instability caused by high cutting speed that affects the cutting characteristics such as cutting force and tool wear. Cutting characteristics are measured and analyzed through cutting force, FFT analysis of cutting force and tool wear along cutting length according to low tool paths with same metal removal rate. As a results of the experiments, this study suggests the optimal conditions of tool path and cutting direction. This approach for the cutting characteristics of semi-finishing provides a useful aid for the productivity and efficiency improvements of NC machining processes.

• 대한기계학회논문집A
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• 제24권10호
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• pp.2589-2596
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• 2000

As current manufacturing processes require high spindle speed and precise machining, increasing accuracy by reducing volumetric errors of the machine itself, particularly thermal errors, is very important. Thermal errors can be estimated by many empirical models, for example, an FEM model, a neural network model, a linear regression model, an engineering judgment model, etc. This paper discusses to make a modeling of thermal errors efficiently through backward elimination and fuzzy logic strategy. The model of a thermal error using fuzzy logic strategy overcomes limitation of accuracy in the linear regression model or the engineering judgment model. It shows that the fuzzy model has more better performance than linear regression model, though it has less number of thermal variables than the other. The fuzzy model does not need to have complex procedure such like multi-regression and to know the characteristics of the plant, and the parameters of the model can be mathematically calculated. Also, the fuzzy model can be applied to any machine, but it delivers greater accuracy and robustness.

• 한국기계가공학회지
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• 제15권5호
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• pp.1-7
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• 2016

In the present study, a plastic surface end-milling was implemented to investigate the effects of processing parameters on surface quality. The end milling can be considered an efficient method for rapid prototyping of thermoplastic bio-systems since it exhibits several beneficial functions including short fabrication time and high dimensional accuracy. In this regard, putative biocompatible thermoplastic materials, such as PMMA, PET, and PC, were chosen as workpiece materials. Among the relevant processing parameters influencing the surface quality of the final product, depth of cut, feed rate, and spindle speed were considered in the present study. The roughness of surfaces machined under various conditions was measured to elucidate the effect of each parameter. We found that the cut depth was the most significant factor. Heat generation during machining also had a remarkable effect. From these investigations, an appropriate combination of processing conditions specific to each type of use and end-product could be found. This optimization can be useful in end-milling of thermoplastic bio-systems.

• 한국공작기계학회:학술대회논문집
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• 한국공작기계학회 2000년도 춘계학술대회논문집 - 한국공작기계학회
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• pp.537-542
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• 2000

Wire deflection, surface roughness and roundness were observed on changing discharge time for electrical discharge machining(EDM) of STD-11 in various conditions of thickness. The wire deflection was decreased as increasing discharge time and wire tension. The deflection is the smallest at the speed of wire of 10.6m/min and the water specific resistivity of 5k$\Omega$.cm. The deflection is found to be decreased as increasing dwell time. But if the water pressure is high, it is found not to be changed after the vibration of 4sec. The component of copper(Cu) and zinc(Zn), which is the main material of wire electrode, is observed for rough wire-cutting EDM of STD-11. This phenomena is found to be similar in spite of the change of EDM energy level. But it will be improved by changing the material and the shape of wire. The roundness of middle is found to be worse than that of upper and it is increased as the thickness of material is increased.

• 한국정밀공학회지
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• 제19권9호
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• pp.125-132
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• 2002

We use a compound-cam twin arm structure and random tool access method to achieve a faster ATC (Automatic Tool Changer) system for the accurate position and rotation control of a tool magazine and an exchange am. Based on the data obtained from various sensors, it is possible to follow the sequence of commands in each control step for an exchange arm. However, it is not so easy to reduce the exchange time of the system because of the slow responses of the sensors and execution mode delays of PLC (Programmable Logic Controller) scan time. In this paper, we propose a new programmed limit-switch position control method to obtain the shortest possible delays for the random tool access method and compound-cam twin arm structure. With some experimental results, we have achieved below 0.9sec tool exchange time with the proposed method.

• 제어로봇시스템학회논문지
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• 제22권10호
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• pp.847-852
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• 2016

In this paper, important design parameters for parallel kinematic robots are defined, paying special attention to machining errors which may cause kinematic errors at the end effector of a robot. The kinematic effects caused by each design parameter, as well as their upper/lower limits, are analyzed here. To do so, we have developed a novel software program to compute kinematic errors by considering its defined design parameters. With this program, roboticists designing parallel kinematic robots can understand the important design parameters for which upper/lower allowances have to be strictly controlled in the design process. This tactic can be used for the design of high-speed, parallel kinematic robots to reduce the design/manufacturing costs and increase kinematic precision.

• 한국공작기계학회:학술대회논문집
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• 한국공작기계학회 1999년도 춘계학술대회 논문집
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• pp.75-80
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• 1999

As current manufacturing processes require high spindle speed and precise machining, increasing accuracy by reducing volumetric errors of the machine itself, particularly thermal errors, is very important. Thermal errors can be estimated by many empirical models, for example, an FEM model, a neural network model, a linear regression model, an engineering judgment model etc. This paper discusses to make a modeling of thermal errors efficiently through backward elimination and fuzzy logic strategy. The model of a thermal error using fuzzy logic strategy overcome limitation of accuracy in the linear regression model or the engineering judgment model. And this model is compared with the engineering judgment model. It is not necessary complex process such like multi-regression analysis of the engineering judgment model. A fuzzy model does not need to know the characteristics of the plant, and the parameters of the model can be mathematically calculated. Like a regression model, this model can be applied to any machine, but it delivers greater accuracy and robustness.

• 한국기계가공학회지
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• 제18권10호
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• pp.60-67
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• 2019

Recently, lightweight materials such as Ti alloys have been used increasingly in the aerospace and high-tech industries for weight loss and fuel efficiency. Because of built-up edges and workpiece deflection due to low stiffness, the Ti alloys have poor machinability. In our study, systematic experiments were conducted to investigate the milling characteristics of the Ti alloy (Ti-6A1-4V) with endmills. The independent variables in the experiment were spindle speed, feed per tooth, and axial depth. Cutting force, acceleration RMS, and surface roughness were measured. Using the response surface method, the optimal cutting conditions were analyzed to improve machining quality and productivity.

• 한국기계가공학회지
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• 제20권9호
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• pp.90-96
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• 2021

As real-time data of factories can be collected using various sensors, the adaptation of intelligent unmanned processing systems is spreading via the establishment of smart factories. In intelligent unmanned processing systems, data are collected in real time using sensors. The equipment is controlled by predicting future situations using the collected data. Particularly, a technology for the prediction of tool wear and for determining the exact timing of tool replacement is needed to prevent defected or unprocessed products due to tool breakage or tool wear. Directly measuring the tool wear in real time is difficult during the cutting process in milling. Therefore, tool wear should be predicted indirectly by analyzing the cutting load of the main spindle, current, vibration, noise, etc. In this study, data from the current and acceleration sensors; displacement data along the X, Y, and Z axes; tool wear value, and shape change data observed using Newroview were collected from the high-speed, two-edge, flat-end mill machining process of SKD11 steel. The support vector machine technique (machine learning technique) was applied to predict the amount of tool wear using the aforementioned data. Additionally, the prediction accuracies of all kernels were compared.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2002년도 춘계학술대회 논문집
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• pp.108-113
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• 2002

This paper presents a multi-step structural design optimization method fur machine tool structures using a genetic algorithm with dynamic penalty. The first step is a sectional topology optimization, which is to determine the best sectional construction that minimize the structural weight and the compliance responses subjected to some constraints. The second step is a static design optimization, in which the weight and the static compliance response are minimized under some dimensional and safety constraints. The third step is a dynamic design optimization, where the weight static compliance, and dynamic compliance of the structure are minimized under the same constraints. The proposed design method was examined on the 10-bar truss problem of topology and sizing optimization. And the results showed that our solution is better than or just about the same as the best one of the previous researches. Furthermore, we applied this method to the topology and sizing optimization of a crossbeam slider for a high-speed machining center. The topology optimization result gives the best desirable cross-section shape whose weight was reduced by 38.8% than the original configuration. The subsequent static and dynamic design optimization reduced the weight, static and dynamic compliances by 5.7 %, 2.1% and 19.1% respectively from the topology-optimized model. The examples demonstrated the feasibility of the suggested design optimization method.