• Journal of the Korean Society for Precision Engineering
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• v.20 no.7
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• pp.227-232
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• 2003

In order to make a deep and precise micro-hole, electrode wear and clearance between the electrode and the workpiece are important parameters using micro-electrical discharge machining. In this study, experiments were carried out to show the characteristics of electrode wear and radial clearance with respect to the depth of machined hole. Electrode wear varied with respect to the depth of hole. With deeper machined hole, bigger clearance was observed. Also it was found that the diameter of electrode influences machining characteristics of deep holes.

• Composites Research
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• v.25 no.6
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• pp.186-190
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• 2012

With the wide application of fiber-reinforced composite material in aero-structures and mechanical parts, composite joint have become a very important research area because they are often the weakest sites in composite structures. In this paper, the failure strengths of the bolted joint and pin joint which have variable hole clearance were evaluated and compared. From the tests, the first failure loads of the bolted joint and pin joint with $880{\mu}m$ hole clearance have decreased by 24.2 % and 51.3 % compared to those of joints with $0{\mu}m$ hole clearance, respectively. Also, the failure index of the joints were calculated by the finite element method and compared with experimental results.

• Journal of the Korea Furniture Society
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• v.28 no.1
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• pp.53-59
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• 2017

Wooden dowels are commonly used to join the particleboard members together in many types of structures, But little information is available concerning their holding properties in domestic particleboard. This study was performed to determine the withdrawal loads and strengths on the effect of diameter of dowel and hole clearance. The test block was manufactured from 15 mm thick domestic particleboard. The dowel was manufactured 6, 8 and 10 mm diameters from korean castanea, korean pine and tuliptree. Research reported here indicates that withdrawal loads increase, but withdrawal strengths decrease, as the dowel diameter increases. This study also indicates that dowel withholding load and strength for particleboard less decrease than those for domestic wood as a hole clearance decreases.

• Journal of Mechanical Science and Technology
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• v.18 no.10
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• pp.1849-1858
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• 2004

For examining friction-factor characteristics of round-hole pattern surfaces which are usually applied on damper seals, flat plate test apparatus is designed and fabricated. The measurement method of leakage and pressure distribution along round-hole pattern specimen with different hole area is described and a method for determining the Fanning friction factor is discussed. Results show that the round-hole pattern surfaces provide a much larger friction factor than smooth surface, and the friction factor vs. clearance behavior yields that the friction factor generally decreases as the clearance increases unlike the results of Nava's flat plate test. As the hole depth is decreased, the friction factor is increased, and maximum friction factor is obtained for 50% of hole area. Since the present experimental friction factor results show coincident characteristics with Moody's friction factor model, empirical friction factors for round-hole pattern surfaces are obtained by using the Moody's formula based on curve-fit of the experimental data. Results of Villasmil's 2D CFD simulation support the present experimental test result.

• The KSFM Journal of Fluid Machinery
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• v.13 no.6
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• pp.5-12
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• 2010

Comparative study on the flow measurement by 5-hole and 7-hole probes was conducted in a linear cascade with tip clearances of 2.3%, 3.1%, and 4.4% of the blade span. Calibration range of the 5-hole and the 7-hole probes were ${\pm}25$ and ${\pm}50$ degrees, respectively. Results show that the secondary flow and total pressure loss measured by the 5e-hole and 7-hole probes were similar at small tip clearance cases. However, at the tip clearance of 3.1% and 4.4% of the blade span cases, flow angles exceeding the calibration range of the 5-hole probe were observed. Because of the wider calibration range, larger flow angle by strong leakage vortex could be measured by the 7-hole probe.

• Transactions of Materials Processing
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• v.23 no.1
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• pp.23-28
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• 2014

The aspect ratio of a hole is defined as the ratio of the thickness to the diameter of the sheet metal. Most holes in the sheet metal industry are made by piercing. However, for thick sheets, which have an aspect ratio greater than 2, a machining process like drilling instead of piercing is usually used to make holes. In the current study, piercing, which is a shearing process, is evaluated to punch a hole with a high aspect ratio by using a newly designed die set-up. The piercing die was manufactured to prevent the punch from buckling and also to improve the alignment between the die components. An aluminum alloy sheet was selected for the experiments. The influence of several process parameters such as sheet thickness, clearance and stripping force were investigated. Experimentally, a hole with an aspect ratio of 5 was pierced. The resulting hole had a clean surface and the dimensional accuracy of pierced hole was considerably improved with decreasing clearance between punch and die. It is also shown that the larger penetration depth of the effective sheared surface can be achieved for high aspect ratio piercing relative to conventional piercing with a low aspect ratio.

• Transactions of Materials Processing
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• v.13 no.3
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• pp.190-204
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• 2004

The objective of this study is to develop a highly accurate micro tool alignment system applicable to the micro machining technology. In a specific application such as micro hole punching, radial clearance between micro tools is order of a few micron. Under this micron scale tool clearance, accuracy of tool alignment is very important for ensuring hole quality. In the present study, a two-way image acquisition system was developed, which can produce overlapped image of both micro tools that face each other, and applied to the tool alignment in the micro punching. Also, to meet alignment accuracy of tools within $1\mu\textrm{m}$, the cross correlation image processing algorithm was employed. With this system, $25\mu\textrm{m}$ punching tools with $1\mu\textrm{m}$ radial clearance could be accurately aligned.

• Journal of the Korean Wood Science and Technology
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• v.44 no.5
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• pp.736-742
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• 2016

Wooden dowels are commonly used to join the wooden members together in many types of structures, But little information is available concerning their holding properties in domestic wood. This study was performed to determine the withdrawal loads and strengths on the effect of diameter of dowel and hole clearance. The test block was manufactured from 15 mm thick korean red pine and korean pine. The dowel was manufactured 6, 8 and 10 mm diameters from korean castanea, korean pine and tuliptree. Research reported here indicates that withdrawal loads increase, but withdrawal strengths decrease, in a linear fashion as the dowel diameter increases. This study also indicates that dowel withholding load and strength increase in a linear fashion as a hole clearance decreases.

• Journal of Advanced Marine Engineering and Technology
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• v.26 no.3
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• pp.353-361
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• 2002

The tip leakage flow passing through the clearance between rotor blade tip and casing shroud has been known to occupy an important portion of the rotor overall loss. In this study, flow characteristics in axial flow rotors with different tip clearances is investigated by experimental and numerical methods. The experimental study was carried out to measure static pressure and velocity profiles at the real rotating test rig. The axial flow rotors used for the experiments have ten blades and three different rotor diameter. The tip clearance heights are 1mm, 3mm, and 4.5mm. Measurements were done using spherical type five-hole probe by non-nulling method. The numerical study was carried out to calculate pressure distributions and velocity vectors at the same condition as the experiments in the flow fields of axial flow rotors using Phoenics code.

• Transactions of Materials Processing
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• v.14 no.3 s.75
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• pp.277-281
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• 2005

LTCC(Low temperature co-fired ceramic) is being recognized as a significant packaging material of electrical devices for the advantages such as relatively low temperature being needed for process, low conductor resistance and high printing resolution. In the process of LTCC electrical devices, the punched via-hole quality is one of the most important factors on the performance of the device. However, its mechanism is very complicated and optimization of the process seems difficult. In this paper, to clarify the process, via-hole punching experiments were carried out and the punched holes were examined in terms of their burr formation. The effects of thickness of PET sheet, ceramic sheet and punch-to- die clearance on via-hole quality were also discussed. Optimum process conditions are proposed and a factor $\kappa$ is introduced to express effect of the process variables.