• Journal of the Korean Society for Precision Engineering
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• v.14 no.8
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• pp.21-28
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• 1997

This paper presents the influence of the process parameters on the change in dynamic behavior of a lathe turning system. With variation of feed rate, depth of cut, direction of tool motion, cutting speed and tool location along the workpiece, the dynamic characteristics of stable cutting, chatter transition and fully developed chatter regions are demonstrated. The workpiece vibration during machining is continuously measured at different tool locations along the workpiece and quantitatively analyzed. Complex linear behavior due to change of process parameter values as well as fundamental wystem nonlinearity due to change of process configuration indicated by a tool path dependence of the locations of chatter onset and disappearance are described. Finally, the structural characteristics of the turning system which can have large and nonlinear effects on system behavior are presented.

• Korean Journal of Materials Research
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• v.15 no.11
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• pp.705-710
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• 2005

NIL (nanoimprint lithography) technique has demonstrated a high potential for wafer size definition of nanometer as well as micrometer size patterns. During the replication process by NIL, the stiction between the stamp and the polymer is one of major problems. This stiction problem is moi·e important in small sized patterns. An antistiction layer prevents this stiction ana insures a clean demolding process. In this paper, we were using a TCP (transfer coupled plasma) equipment and $C_4F_8$ as a precursor to make a Teflon-like antistiction layer. This antistiction layer was deposited on a 6 inch silicon wafer to have nanometer scale thicknesses. The thickness of deposited antistiction layer was measured by ellipsometry. To optimize the process factor such as table height (TH), substrate temperature (ST), working pressure (WP) and plasma power (PP), we were using a design of experimental (DOE) method. The table of full factorial arrays was set by the 4 factors and 2 levels. Using this table, experiments were organized to achieve 2 responses such as deposition rate and non-uniformity. It was investigated that the main effects and interaction effects between parameters. Deposition rate was in proportion to table height, working pressure and plasma power. Non-uniformity was in proportion to substrate temperature and working pressure. Using a response optimization, we were able to get the optimized deposition condition at desired deposition rate and an experimental deposition rate showed similar results.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.39 no.9
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• pp.923-928
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• 2015

In this paper, we propose an ultrasonic magnetic abrasive polishing (US-MAP) technique to effectively machine a high-strength material, and we prove the efficiency of hybrid finishing. We use Taguchi's experimental method to determine the influence of each parameter. Based on the results, US-MAP exhibited a higher polishing efficiency than traditional MAP, and a suitable frequency for hybrid finishing was 28 kHz. When investigating the effect of the parameters on the surface roughness, the ultrasonic amplitude had the greatest effect. However, when machining with $55-{\mu}m$ amplitude, the machining efficiency decreased as the magnetic flux density varied.

• Korean Journal of Materials Research
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• v.20 no.11
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• pp.559-569
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• 2010

The liquid-phase sintering method was used to prepare a glass lens forming core composed of SiC-$Al_2O_3-Y_2O_3$. Spark plasma sintering was used to obtain dense sintered bodies. The sintering characteristics of different SiC sources and compositions of additives were studied. Results revealed that, owing to its initial larger surface area, $\alpha$-SiC offers sinterability that is superior to that of $\beta$-SiC. A maximum density of $3.32\;g/cm^3$ (theoretical density [TD] of 99.7%) was obtained in $\alpha$-SiC-10 wt% ($6Al_2O_3-4Y_2O_3$) sintered at $1850^{\circ}C$ without high-energy ball milling. The maximum hardness and compression stress of the sintered body reached 2870 Hv and 1110 MPa, respectively. The optimum ultra-precision machining parameters were a grinding speed of 1243 m/min, work spindle rotation rate of 100 rpm, feed rate of 0.5 mm/min, and depth of cut of $0.2\;{\mu}m$. The surface roughnesses of the thus prepared final products were Ra = 4.3 nm and Rt = 55.3 nm for the aspheric lens forming core and Ra = 4.4 nm and Rt = 41.9 for the spherical lens forming core. These values were found to be sufficiently low, and the cores showed good compatibility between SiC and the diamond-like carbon (DLC) coating material. Thus, these glass lens forming cores have great potential for application in the lens industry.

• Journal of Korean Tunnelling and Underground Space Association
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• v.8 no.2
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• pp.183-196
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• 2006

Rock joint roughness obtained from the camera-type 3D scanner was classified into waviness and unevenness. The classification criteria were established in the previous study; digital filtering was used to distinguish one from another. The classified and original profiles were used to produce metal moulds. For accurate machining of the moulds, the WEDM(Wire-cut Electric Discharge Machining) was adopted. Specimens were cast using high strength gypsum, and joint shear tests were performed by varying normal stress from low value to high one. Roughness mobilization characteristics depending on the asperity scale and the applied normal stress were investigated. A new equation was proposed to predict shear strength of rock joint, which can consider the characteristics of roughness mobilization and roughness parameters. The roughness quantification composed of waviness and unevenness was found to be a useful method to predict the joint shear strength.

• Korean Chemical Engineering Research
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• v.47 no.1
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• pp.72-78
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• 2009

For the electro-discharge machining of an electro-conductive anisotropic composite, an unsteady state formulation was established and solved by Galerkin's finite element method. The distribution of temperature on work piece, the shape of the crater and the material removal rate were obtained in terms of the process parameters. The $12{\times}12$ irregular mesh that was chosen as the optimum in the previous analysis was used for computational accuracy and efficiency. A material having the physical properties of alumina/titanium carbide composite was selected and an electricity with power of 51.4 V and current of 7 A was applied, assuming the removal efficiency of 10 % and the thermal anisotropic factors of 2 and 3. As the spark was initiated the workpiece immediately started to melt and the heat affected zone was formed. The moving boundary of the crater was also identified with time. When the radial and axial conductivities were increased separately, the temperature distribution and the shape of the crater were shifted in the radial and axial directions, respectively. The material removal rate was found to be higher when the conductivity was increased in the radial direction rather than in the axial direction.

• Journal of Korean Society of Industrial and Systems Engineering
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• v.44 no.4
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• pp.12-22
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• 2021

This article suggests the machine learning model, i.e., classifier, for predicting the production quality of free-machining 303-series stainless steel(STS303) small rolling wire rods according to the operating condition of the manufacturing process. For the development of the classifier, manufacturing data for 37 operating variables were collected from the manufacturing execution system(MES) of Company S, and the 12 types of derived variables were generated based on literature review and interviews with field experts. This research was performed with data preprocessing, exploratory data analysis, feature selection, machine learning modeling, and the evaluation of alternative models. In the preprocessing stage, missing values and outliers are removed, and oversampling using SMOTE(Synthetic oversampling technique) to resolve data imbalance. Features are selected by variable importance of LASSO(Least absolute shrinkage and selection operator) regression, extreme gradient boosting(XGBoost), and random forest models. Finally, logistic regression, support vector machine(SVM), random forest, and XGBoost are developed as a classifier to predict the adequate or defective products with new operating conditions. The optimal hyper-parameters for each model are investigated by the grid search and random search methods based on k-fold cross-validation. As a result of the experiment, XGBoost showed relatively high predictive performance compared to other models with an accuracy of 0.9929, specificity of 0.9372, F₁-score of 0.9963, and logarithmic loss of 0.0209. The classifier developed in this study is expected to improve productivity by enabling effective management of the manufacturing process for the STS303 small rolling wire rods.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.19 no.6
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• pp.73-79
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• 2020

Although engineering plastics that are light-weight and have excellent mechanical performance have been widely applied in various industries in place of steel structures to reduce the burden of cost and time, there have been few studies related to their surface roughness. This study aims to evaluate the optimal effects of feed rate, cutting speed, and depth of cut as cutting parameters as well as nose angle on the surface characteristics of MC nylon in CNC lathe machining. To determine the best conditions under different nose radii, the experiments were performed based on the Taguchi L9(34) orthogonal array method, in which the resulting data was analyzed using the S/N ratio and ANOVA. Results indicate that the most significant contribution was feed rate followed by nose angle and cutting speed, whereas the depth of cut did not influence the performance. This study demonstrates that the suggested method for improving the surface finishing of MC nylon is efficient compared with results obtained from experimentation and prediction.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.28 no.6
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• pp.860-866
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• 2004

In the end milling operation the deflection of the cutter is an important factor affecting the accuracy of machining, with implications on the selection of cutting parameters and economics of the operation. Several studies were devoted to the end mill deflection and its effects, notably, providing a useful insight into the problem. Although the deflection affects adversely the accuracy, the flexibility of the cutter is beneficial in attenuating the overload in a sudden transient situation, as well as in attenuating chatter. The deflection of the end mill was studied both experimentally with strain gauge, tool dynamometer, laser measuring apparatus and on a finite element model of the cutting using ANSYS software. The deflection of machining tool with various helix angles was studied with FEM simulation and experiment. ANSYS analysis performed on the finite element model of the end mill provides deflection results which agree within 15.0% with the experimental ones.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.06a
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• pp.1597-1600
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• 2005

Recently, the trends of TFT-LCD are large scale and thin thickness, so, the demands of Light Guide Panel(LGP) which is able to substitute for prism sheets are appeared. Functions of LGP obtaining polarization of light of the prism sheet as well as the incidence and reflection of light are demanded. This prismless type LGP to complete functions of the existing LGP and polarization at once must be supported by micro machining technology of LGP surface. In this research, we have used the STAMPER method for the mass product and In-Line process, and the optimized conditions are established by analyzing the cutting force and conditions according to the material and processing properties when the prismless type LGP mold is fabricated. Parameters of the cutting condition were the workpiece and cutting depth.