A femtosecond laser is used in various fields such as microscale machining, OLED repair, micro 3D structure fabrication, and eye surgery. Particularly, because of non-thermal property, ablation and ablation threshold are the most representative characteristics of femtosecond laser. The ablation system is accompanied by many optics, stage, or gantry. In the case of the gantry, an ordinary optic system delivers a beam where mirrors and lens are required. If the gantry moves to the sample, external stimulation such as vibration will occur. Vibration has an influence on optics such as transforming beam path and becomes an error that decreases accuracy, precision, and spatial resolution. Generally, Fiber Optic Beam Delivery System (FOBDS) is used to solve this issue. But in the case of the femtosecond laser, FOBDS is incompatible. Recently, another FOBDS model that is compatible with the femtosecond laser has been developed. In this paper, the ablation threshold was obtained by FOBDS and femtosecond laser. The results present a possibility of ablation without external stimulation.
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257 nm Deep UV Femtosecond Laser Ablation with Minimized Crack and Chipping on Display Ultra-Thin Glass Kwangwoo Cho, Junha Choi, Changdeok Ko, Muhyun Kim, Joohan Lee, Eunhyang Eom, Sung-Hak Cho International Journal of Precision Engineering and Manufacturing.2024; 25(2): 271. CrossRef
Chemical mechanical planarization (CMP) is a wafer planarization process that uses chemical reactions initiated by slurry and mechanical actions by pad asperity. The progression of CMP causes temperature deviation on the pad surface. Increase in process temperature results in increased material removal rate (MRR). So, pad temperature distribution is closely related to With-In Wafer Non-Uniformity (WIWNU). In this study, the pad temperature distribution is modelled from the energy perspective and slurry supply location is suggested to reduce temperature deviation. An energy supplying expression was created by setting the micro area and substituting the applied pressure, relative velocity, and process time. The energy and temperature distributions were observed as quite consistent and the temperature peak matched well with highest friction heat point (HFHP). Based on the model expression, the slurry injection position was set to the center of pad, the HFHP and wafer center, and change in temperature distribution was measured. A comparative analysis was carried out employing the existing method that uses multiple nozzles rather than single nozzles and the deviation was reduced by about 18.5% when slurry was supplied to the HFHP for a single nozzle and by 24.7% when the largest flow rate was supplied for multiple nozzles.
The directed energy deposition (DED) process has been used for enhancement of the mechanical property, repair, and part manufacturing. Post-process machining is required due to the low quality of the DED printed part. Even if the part is printed under similar conditions, dimensional variations occur frequently due to the accumulation of small printing errors. Due to tool overfeeding and the occurrence of the non-cutting area due to this variation, the quality of the finished part is not guaranteed. Therefore, the post-process machining should be carried out considering the actual printed part shape. Herein, the flexible post-process machining is proposed by utilizing the shape information through the on-machine measurement (OMM) of DED printed parts. The process margin for machining the design shape is calculated through the OMM of the geometric dimension of the printed part. Feedrate (Override) and machining path of each printing parts are flexibly determined depending on the process margin. This technique is applied to the pocket shape part printed with STS 316L material, and the rough and finish machining conditions are established. Rough machining time was reduced by adjusting the feedrate flexibly. The final form of accuracy and surface roughness were achieved under 30 and 0.25 μm, respectively.
In this study, a free-fall drop tester was studied to test the impact reliability of small electronic components. The electronic component was fixed to the drop table and the table was fallen along guide rods. The impact energy was adjusted by the initial drop height, and the impact duration time was adjusted by inserted soft layers under the drop table. Table acceleration was achieved in the form of a half-sine that conforms to international standards. The developed tester was evaluated by a small printed circuit board. It was observed that the developed tester was fully utilized for the impact reliability assessment of electronic components.
This study is to numerically investigate the Aero-Acoustics of Turbocharger compressor. The turbocharger compressor is high-speed turbomachinery that rotates faster than 200,000 RPM. The Aero-Acoustics with five different rotational speeds (120,000, 150,000, 180,000, 200,000, and 220,000 RPM) is used herein. The fluid domain is designed by CATIA V5R21 and analyzed by ANSYS FLUENT V19.1 with compressible momentum equation. The Pressure-velocity coupling method of the solver is the coupled algorithm and calculated by a pressure-based method. Numerical analysis of the aero-acoustics by broadband noise sources model provides calculated sound-source and acoustic-level based on steady RANS. At the industrial site, it is important to quickly analyze the noise source. APL (Acoustic Power Level) with five different rotational speeds and sound characteristics based on flow factor at the compressor wheel was numerically calculated for the noise-based design. The maximum APL is located at blade tips in case of 120,000, 150,000 and 180,000 RPM. In the case of 200,000 RPM, the maximum APL is located at splitter tips. At more than 220,000 RPM, the maximum APL is located at the balancing cutting section of the wheel. In order to optimally design the high-speed turbomachinery, cutting sections and side locations of the wheel are essential factors to reduce physical noise.
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Elastomeric bushings are structural elements and used in automotive suspension systems. An idealized bushing is an elastomeric hollow cylinder between an outer steel cylindrical sleeve and an inner steel cylindrical rod. The outer sleeve is connected with the components of the suspension system and transfer forces and moments from the wheel to the chassis. The accurate determination of the transmitted forces and moments among autocomponents, the motion of the components, the stresses in the components, and energy dissipation are affected by the quality of the elastomeric bushing model. Force- Displacement relation, moment-rotational angle relation, and coupled relations for elastomeric bushings are imperative for multi-body dynamics simulations. The boundary value problem in the bushing response leads to force-displacement relation and moment-rotational angle relations which require extensive computation time for implementation. Herein, an explicit moment-rotational angle relation has been introduced for use in multi-body dynamics simulations, a modified Pipkin-Rogers model is proposed and a boundary value problem is formulated for torsional mode elastomeric bushing response. Lianis" experimental equation and Pipkin-Rogers model are used for numerical experimental research. The proposed method and the prediction of the proposed moment-rotational angle relation are observed to exhibit excellent agreement with the original results.
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Frequency Related Verification of MPR Model of Elastomeric Bushing in Torsional Mode Seong Beom Lee Journal of the Korean Society for Precision Engineering.2021; 38(12): 959. CrossRef
The automobile horn system is an essential part that produces sound for safety reasons. Production of horn system is classified based on two main processes. One of them is the caulking process which makes body assembly and forms the lower part of the horn system. The control dimension of body assembly is a crucial factor for quality control as the sound of the horn is largely determined by the control dimension. In this paper it has been found that plastic deformation of body and its restoration after caulking process is the main reason for the change in control dimension. Typically, 100 specimens of the body assembly were employed and the results were compared (Restore the Length of the Body) with another data set that had the same body but different parts in the assembly. Monte carlo simulation was used for tolerance analysis of control dimension for the body assembly including the deformation of the body in the caulking process. The simulation was identified as a good model to predict the satisfaction ratio of the control dimension with high accuracy and was observed to be useful in designing parts of the assembly and equipment used in the caulking process.
In winter, electric power facilities such as solar panels, substations, power towers, and power lines suffer from freezing or ice accumulation problems due to exposure to harsh external environments. These problems result in unstable power supply, high maintenance costs, and severe economic and social losses. To address these problems, diverse anti-icing or deicing techniques including physical, thermal, and chemical approaches have been developed. However, these conventional approaches have limitations such as requirements for additional external energy, environmental toxicity, and low applicability. Recently, novel anti-icing surfaces based on unique drop bouncing dynamics have been developed by mimicking nano/micro-structures of natural systems. These anti-icing surfaces have attracted attention due to their high energy efficiency and environmental friendliness. It has been found that the superhydrophobic surfaces with specific nano/micro-structures can effectively remove the water droplets before the formation of ice nucleation by minimizing contact area and contact time between the droplets and the surface, thereby demonstrating excellent anti-icing properties. This review introduces recently developed anti-icing techniques based on the drop bouncing dynamics, and briefly describes the future direction of the anti-icing technology for stable power supply.
Additive manufacturing processes have been called by a wide variety of terms since the early days of development. As these names are often mixed academically and industrially, the demand for standardization of terms has gradually increased. Accordingly, the American Society for Testing Materials (ASTM) and the International Organization for Standardization (ISO) are in the process of establishing standards for the names and definitions of important terms related to additive manufacturing. Although Korea has also begun to establish KS standards based on ISO/ASTM standards, the Korean language and definitions of important terms related to additive manufacturing as defined by ISO/ASTM have not been fully organized. Therefore, the similar terms defined in ISO/ASTM in many academic and industrial literature are called by various Korean terms. Thus, this work deals with suggestions on the Korean terminologies and standardization of important terms related to additive manufacturing based on ISO/ASTM standards. Especially, this paper deals with the Additive Manufacturing and seven sub-process classifications.
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