• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2002년도 춘계학술대회 논문집
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• pp.947-951
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• 2002

During the hotwire cutting of EPS foam sheet, the dimensional accuracy and part quality of the cut par are highly dependent upon the thermal field in the EPS. The thermal field is determined by operating parameters such as heat input, cutting speed and cutting angle. The objective of this study is to investigate into the influence of cutting angle on the kerfwidth and part quality of the cut part in hotwire cutting of EPS foam using the experiments and the numerical analysis in the case of a single sloped cutting. In order to estimate an accurate temperature field, the transient thermal analysis using a moving coordinate system and the sloped heat flux model is carried out. From the results of the experiments and the analysis, it has been found that the effect of cutting angle on the kerfwidth and the melted area at the edge are 0.1 mm and 0.11 m$m^2$ respectively. The results of the experiments show that the surface roughness is not appreciably influenced by the cutting angle.

• 한국정밀공학회지
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• 제22권10호
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• pp.26-30
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• 2005

• Wind and Structures
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• 제26권5호
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• pp.317-329
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• 2018

Wake characteristics of the flow over a finite square prism at different incidence angles were experimentally investigated using an open-loop wind tunnel. A finite square prism with a width D = 15 mm and a height H = 7D was vertically mounted on a horizontal flat plate. The Reynolds number was varied from $6.5{\times}10^3$ to $28.5{\times}10^3$ and the incidence angle ${\alpha}$ was changed from $0^{\circ}$ to $45^{\circ}$. The ratio of boundary layer thickness to the prism height was about ${\delta}/H=7%$. The time-averaged velocity, turbulence intensity and the vortex shedding frequency were obtained through a single-component hotwire probe. Power spectrum of the streamwise velocity fluctuations revealed that the tip and base vortices shed at the same frequency as that ofspanwise vortices. Furthermore, the results showed that the critical incidence angle corresponding to the maximum Strouhal number and minimum wake width occurs at ${\alpha}_{cr}=15^{\circ}$ which is equal to that reported for an infinite prism. There is a reduction in the size of the wake region along the height of the prism when moving away from the ground plane towards the free end.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2001년도 춘계학술대회 논문집
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• pp.910-913
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• 2001

Rapid Prototyping(RP) techniques have unique characteristics according to their working principle: the stair-stepped surface of a part due to layer-by-layer stacking, low building speed, and additional post-processing to improve surface roughness. A new RP process, Variable Lamination Manufacturing by using expandable polystyrene foam(VLM-S), has been developed to overcome the unfavorable characteristics. The objective of this study is to investigate the thermal characteristics and skeleton size effects as the hotwire cuts EPS foam sheet in order to improve dimensional accuracy of the parts, which is produced by VLM-S. Empirical and analytical approaches are performed to find the relationship between cutting speed and heat input, and the relationship between maximum available cutting speed and heat input. In addition, empirical approaches are carried out to find the relationship between cutting error and skeleton size, and cutting deviation and skeleton size. Based on these results, the optimal hotwire cutting condition and available minimum skeleton size are derived. The outcomes of this study are reflecting in the enhancement of VLM-S input data generation S/W.

• 한국정밀공학회지
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• 제34권1호
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• pp.35-39
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• 2017

We used a construction method using a CNC milling machine, where free-formed molds were made by cutting EPS (Expanded PolyStyrene) foam with the CNC machine, to build free-formed buildings. CNC milling is off-the-shelf technology that can easily cut EPS foam; however its production cost is too high and the time to manufacture an EPS mold is too long. This paper proposes a novel cutting machine with a fast and cost effective mechanism to manufacture EPS concrete molds. Our machine comprises a cutter and Cartesian coordinate type moving mechanism, where the cutter cuts EPS foam using a hotwire in the shape of '$\sqcap$' and is capable of adjusting its cutting angle in real-time while keeping its cutting width. We proved through cutting experiments on the CNC machine that cutting time was greatly shortened compared to the conventional method and that the resulting concrete mold satisfied manufacturing precision.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2002년도 추계학술대회 논문집
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• pp.176-180
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• 2002

All types of VLM-s process include the linear heat cutting of EPS foam to generate a layer with 3D shape. The dimensional accuracy and part quality of the cut part are dependent on the thermal characteristics in the EPS foam. The thermal characteristics are determined by operating parameters such as an effective heat input and cutting angle. The objective of this study is to investigate into the influence of cutting angle on the kerfwidth and the melted length of the cut part using the numerical analysis and the experiments in generally sloped cutting with two cutting angles. In order to estimate an accurate temperature field, the transient thermal analysis using moving coordinate system, the fully conformed mesh and the heat flux model with two cutting angles is carried out. From the results of the analysis and the experiments, it has been found that the influence of the rotational angle about x-axis in which the rotational axis is normal with hotwire cutting direction is appreciably negligible in comparison with that of the rotational angle about y-axis.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2000년도 추계학술대회 논문집
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• pp.763-766
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• 2000

Rapid Prototyping(RP) techniques have their unique characteristics according to the working principles: stair-stepped surface of parts due to layer-by-layer stackin, low build speed caused by line-by-line solidification to build one layer, and additional post processing to improve surface roughness, so it is required very high cost to introduce and to maintain RP apparatus. The objective of this study is to develop software for automatic generation of unit shape part (USP) for a new RP process, Variable Lamination Manufacturing using linear hotwire cutting technique and expandable polystyrene foam sheet as part material (VLM-S). In order to examine the applicability of the developed software to VLM-S, USP's of general three-dimensional shapes, such as an auto-shift lever knob and a pyramid shape were generated.

• 대한기계학회논문집B
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• 제28권2호
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• pp.230-237
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• 2004

This paper suggests and demonstrates a novel flow measurement technique: tunable AC thermal anemometry that allows simple integration, robust measurement, and extremely high accuracy. The principle and simple theoretical analysis of the technique are presented. To find the optimal condition at which the phase lag becomes most sensitive to flow speed change, the phase lag was measured scanning the heating frequency from 1 to 100 Hz, while the flow speed of ethanol was increased stepwise from 0 to 40 mm/s. The sensitivity of phase lag depended on the heating frequency and the flow speed. It was possible to measure the flow speed of 0.7 mm/s with the resolution of 0.1 mm/s at 4 Hz.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 추계학술대회
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• pp.845-850
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• 2003

Unsteady nature of a tip leakage vortex in an axial flow fan operating at a design and off-design operating conditions has been investigated by measuring the velocity fluctuation in a blade passage with a rotating hotwire probe sensor. Two hot-wire probe sensors rotating with the fan rotor were also introduced to obtain the cross-correlation coefficient between the two sensors located in the vortical flow as well as the fluctuating velocity. The results show that the vortical flow structure near the rotor tip can be clearly observed at the quasi-orthogonal planes to a tip leakage vortex. The leakage vortex is enlarged as the flow rate is decreased, thus resulting in the high blockage to main flow. The spectral peaks due to the fluctuating velocity near the rotor tip are mainly observed in the reverse flow region at higher flow rates than the peak pressure operating condition. However, no peak frequency presents near the rotor tip for near stall condition.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 추계학술대회
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• pp.729-734
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• 2003

This paper reports the characteristics of the three dimensional turbulent flow in the rectangular-sectioned 180 degree bends by Hot-wire anemometer. Grande and Kool proposed a cooling law for the measurements of the flow through the narrow passage. The authors noticed that the calibration coefficients of original method are not constant and fairly sensitive to the flow approaching angle. Measured voltages are converted to three velocity and six Reynolds stress components using the modified method in which the coefficients are treated as a function of approaching angle.