• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.10a
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• pp.502-505
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• 2005

To overcome some of the limitations in the conventional photolithography technique, MC-SPL which has advantages such as flexibility and high speed was developed in the past. To make a fine pattern using MC-SPL, there are many variables to control, for example, applied load, scribing speed, chemical etching condition, and etc. In this work, the effect of contact load on the width of the pattern was investigated. The load not only influences the width of the pattern but it also affects the wear of the probe tip. It was found that it is beneficial to load the tip in two stages. Futhermore, the experimental results showed that the pattern width was more sensitive to the initial contact force.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.2
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• pp.271-277
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• 2013

Skin pass rolling is a very important process for applying a certain elongation to a strip in the cold rolling and annealing processes, which play an important role in preventing the stretching of the yield point when the material is processed. The exact prediction of the rolling force is essential for obtaining a given elongation with the steel grade and strip size. Unlike hot rolling and cold rolling, skin pass rolling is used to apply an elongation of within 2% to the strip. Under a small reduction, it is difficult to predict the rolling force because the elastic deformation behavior of the rolls is complicated and a model for predicting the rolling force has not yet been established. Nevertheless, the exact prediction of the rolling force in skin pass rolling has gained increasing importance in recent times with the rapid development of high-strength steels for use in automobiles. In this study, the possibility of predicting the rolling force in skin pass rolling for producing various steel grades was examined using foil rolling theory, which is known to have similar elastic deformation behavior of rolls in the roll bite. It was found that a noncircular arc model is more accurate than a circular model in predicting the roll force of high-strength steel below TS 980 MPa in skin pass rolling.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.14 no.8
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• pp.3638-3643
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• 2013

These days, workers in a construction site conduct a rebar bending process with a machine. This bending process has some problems such as long processing time and bad quality of the rebar. In order to manufacture a rebar having precision and machinability, we should study on Spring-back phenomenon. This phenomenon affects a shape of rebar after unloading due to restoration ability of material and it is influenced by bending angle, bending radius and a rebar diameter. The change of spring-back ratio according to the change of the parameters are analyzed by FEM. Consequently, Spring-back increases around $0.1^{\circ}$ as bending angle increases $10^{\circ}$. and it also increases around $0.6^{\circ}$ as diameter of rebar increases from ${\varphi}$ 10mm to ${\varphi}$ 16mm. while we can confirm that it decreases around $0.2^{\circ}$ as bending angle increases $10^{\circ}$.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.12 no.12
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• pp.5412-5419
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• 2011

The need is growing for high-speed spindle because various equipment are becoming more precise, miniaturization and high speed with the development of industries. Air-lubricated dynamic bearings are widely used in the optical lithographic manufacturing of wafers to realize nearly zero friction for the motion of the stage. Air-lubricated dynamic bearing can be used in high-speed, high-precision spindle system and hard disk drive(HDD) because of its advantages such as low frictional loss, low heat generation, averaging effect leading better running accuracy. In the paper, numerical analysis is undertaken to calculate the performance of air-lubricated dynamic bearing with herringbone groove. The static performances of herringbone groove bearings which can be used to support the thrust load are calculated. Electrochemical micro machining($EC{\mu}M$) which is non-contact ultra precision machining method has been developed to fabricate the air-lubricated dynamic bearing and optimum parameters which are inter electrode gap size, concentration of electrolyte, machining time are simulated using numerical analysis program.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2007.05a
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• pp.268-271
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• 2007

A sandwich tube is a structured material that has two inner and outer circular tubes and light material between them. In this paper, a sandwich tube with a pyramidal truss core is introduced. Fabrication method and example made by brazing are shown. The behavior of the sandwich tube under lateral loading is predicted by analytical and numerical method. Comparative study between the sandwich and the monocoque tube is performed at a point of view such as strength and weight saving. As a result, proposed tube is appropriate for application to lightweight structural material

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2007.05a
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• pp.314-317
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• 2007

Automotive rear subframe of aluminum tube was developed by using hydroforming process, based on the numerical analysis and physical tryouts. In the previous study, the effect of prebending was evaluated on the basis of forming limit diagram which had been obtained from free bulging, T-shape forming and cross-shape forming, using the developed tube hydroformability testing system. In order to get the sound products, appropriate internal pressure is to be imposed corresponding to the axial feeding. In this study, the loading path, the combination of internal pressure and axial feeding during the process, was optimized to ensure minimum thickness variation and dimensional accuracy, by using response surface method.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2008.10a
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• pp.77-80
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• 2008

Low-cycle fatigue (LCF) tests were carried out to investigate the effect of loading direction on the cyclic deformation behavior and fatigue resistance of rolled AZ31 magnesium alloy. The as-received alloy showed a strong basal texture indicating that the most of basal planes of hexagonal close-packed structure were located parallel to the rolling direction. Two types of specimens whose loading directions were oriented parallel (RD) and vertical (ND) to the rolling direction. respectively, were used for the comparison. It was found that RD specimens yielded at much lower stresses during compression, while vice versa for the ND specimens, which was mainly attributed to the formation of primary twins. This anisotropic deformation behavior resulted in the different mean stresses during the cycling of RD and ND specimens, affecting the fatigue resistance of two specimens. The ND specimen showed a superior fatigue resistance as compared to the RD specimen under strain-controlled condition.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2003.10a
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• pp.168-171
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• 2003

Instrumented indentation tests have been used for estimating material properties. In order to analyze deformation characteristics with various factors, the unloading stiffness should be properly determined from the elastic behaviour. In general, the unloading stiffness is obtained from shifted power functions fitting to indentation unloading curves. But, the functions give often a poor representation of actual data. In this study, control conditions for fitting unloading curves by shifted power functions were investigated. The current efforts may provide useful information about unloading process and valid unloading stiffness.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.3 no.2
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• pp.60-66
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• 2004

Finite element method is very effective method to simulate the forming processes with good prediction of the deformation behaviour. In this paper, It was focussed on the drawability factors on the square cup deep drawing by PAM-STAMP with using magnesium alloy to reduce car weight as well as to draw much attention from the viewpoint of environmental preservation high rigidity, In order to predict the effect of drawability factors, the relationships between punch load and punch stroke, the relationships between thickness strain and distance, and are used. According to this study, the results of simulation will give engineers good information to access the drawability of square cup deep drawing at warm temperature.

• Transactions of Materials Processing
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• v.7 no.2
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• pp.127-138
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• 1998

Process design of multi-step wire drawing process, conducted by means of finite element analysis and ANN(Artificial Neural Network) has been considered. The investigated problem involves the ade-quate selection of the drawing die angle and the correspondent reduction rate in the condition of desired initial and final diameter. Combinations of the process parameters which are used in finite ele-ment simulation are selected by using the orthogonal array. Also the orthogonal array. Also the orthogonal array and the results of finite element simulation which are related to the process energy are used as train data of ANN. In this study it is shown that the application of new technique using ANN and Othogonal array table to the process design of metal forming process is useful method.