Recently, film cooling has been continuously studied to increase the efficiency of gas turbines. A turbine inlet temperature increase occurs as a way to improve the efficiency. However, it is essential to improve the cooling performance of the blade surface because of the melting point of the part. In this paper, a side hole shape wherein a general cylinder hole and two auxiliary holes are combined, is proposed to improve the film cooling efficiency, and the blowing ratio was set to 0.4, 0.8, 1.2, and 2.0. When side hole was applied, the vortex interference at the hole entrance occurred less than that of the cylinder hole. That is, the flow rate of the coolant adsorbed to the surface increased to improve the cooling performance. In conclusion, compared to the cylinder hole, the cooling efficiency of the shape to which the side hole was applied was excellent, and in particular, the average area cooling efficiency with spanwisely designed side holes improved by 83%.
In the selective laser melting (SLM) process, a three-dimensional part is manufactured based on the formation of numerous molten tracks. Consequently, the generated melt pool in the scanning process of each track exhibits close relation to the internal defect formation and the quality of the fabricated part. In this study, a numerical model of single-track scanning of the SLM process is presented to analyze the melt pool characteristics for various process conditions. The presented model considers the thermal behavior of the powder material including the phase change and densification during the SLM process. The temperature-dependent energy absorption and the increase in effective energy absorptivity due to the keyhole mode melting are also incorporated in the heat flux model to evaluate the process conditions in the presence of high energy density. Moreover, the single-track specimens were manufactured under various process conditions for validation of the proposed model. The predicted melt pool dimensions, as well as the melting modes (Conduction/Keyhole), demonstrated good agreement with the experimental measurements. Based on the analysis results, the process boundaries (Keyhole/Lack-of-Fusion) for the SLM process of AlSi10Mg are provided and the potential application of the proposed model for exploring the process window is discussed.
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Extreme gradient boosting-based multiscale heat source modeling for analysis of solid-state phase transformation in additive manufacturing of Ti-6Al-4V Yeon Su Lee, Kang-Hyun Lee, Min Gyu Chung, Gun Jin Yun Journal of Manufacturing Processes.2024; 113: 319. CrossRef
The multi-lumen catheter with complex and small cross section is widely used for interventional radiology and minimally invasive surgery. It is manufactured in the polymer extrusion process with many manufacturing parameters. The profile of the extrudate is difficult to predict because it depends on the die shape and many parameters. In this paper, the effects of the manufacturing parameters for multi-lumen catheter extrusion are studied. The commercial software ANSYS Polyflow is used to simulate the polymer flow and predict the profile of the extrudate. The optimized die shape is used to achieve the target profile of the extrudate. The extrudate profiles are investigated with respect to the puller speeds at the end of the extrudate and blowing air pressure of each lumen. Circularity and major diameter are compared for the different manufacturing parameters. The effects of the manufacturing parameters on the profile of the extrudate are examined. The target profile of the extrudate is obtained with optimized manufacturing parameters.
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Study on Improvement of Catheter Tip Forming Process according to Plating Characteristics in Mold Han Chang Lee, Jinhyuk Jung, Gyu Ik Lee, Woojin Kim, Gyu Man Kim, Bong Gu Lee Journal of the Korean Society for Precision Engineering.2022; 39(9): 711. CrossRef
Development of a Subpath Extrusion Tip and Die for Peripheral Inserted Central Catheter Shaft with Multi Lumen Han Chang Lee, Jinhyuk Jeong, Seunggi Jo, Dong Yun Choi, Gyu Man Kim, Woojin Kim Polymers.2021; 13(8): 1308. CrossRef
A Study on Die Design Optimization for Microcatheter Extrusion Processes Seunggi Jo, Euntaek Lee Journal of the Korean Society of Manufacturing Process Engineers.2021; 20(1): 34. CrossRef
This paper describes the development of a power assistive device controller with user intention detection for fire fighters. In order to detect the intention of users, an F/T sensor frame was designed for the power assistive device controller. Using the numerical approach, each directional strain value of the F/T sensor frame was evaluated singly to determine the optimum point to mount the strain gauge under varying load conditions. The numerical analysis was conducted using the commercial program Ansys v11.0. The finite element model for the F/T sensor frame consisted of 37,547 elements and 157,154 nodes. A sensor bonding device and calibration jig were designed for the F/T sensor frame. In an effort to obtain the decoupling matrix for the F/T sensor frame of the proposed power assist device, calibration tests were conducted in the x-direction, y-direction, z-direction, My-direction and Mz-direction. In addition, the operating system was tested using the power assistive device controller that comprised of the F/T sensor frame.
This study investigates epoxy filling rate in the capillary underfill process of flip-chip packaging when the air is not trapped. Various design features were considered, they include; the shape of soldering bump, inlet size, bump height and bump spacing. The geometric models were made by CATIA and the analysis was carried out using commercial CFD software (Moldex3D capillary underfill packaging). In order to improve the usability of the analysis, the spherical bump shape was authenticated by the means of believe as a rhombic shape, and the analysis results were verified. The inlet size did not in any way whatsoever affect the underfill process analysis. From the analysis, we concluded that the epoxy of center parts needs to fill 80% or more of the inside of the edge in order to keep away from the air trapping on the flip-chip. This result can be a guideline for the underfill process conditions that may not be a reason for the air trap in the flip-chip design and manufacturing.
Polymer microlens manufacturing using thermal reflow was simulated and optimized by a numerical approach. Microlenses are used in various industrial fields, such as optical, semiconductor, and observation experiment equipment. Therefore, polymer microlens fabrication using an economical thermal reflow process is important for mass production and cost reduction. The feasibility of a thermal reflow process for microlens fabrication was analyzed in this paper by numerical methods. First, we refer to the previous studies and papers for the theoretical shape of the microlens. Second, for numerical simulation of the process above Tg (Glass Transition Temperature), we studied the multiphase flow simulation using a VOF method and adopted a Cross-WLF model to consider the rheological characteristics of PMMA. Finally, several parametric studies were carried out to compare the simulation profile and the theoretical lens shape in order to optimize the thermal reflow process. The numerical approach presented in this paper would enable a more efficient analysis and provide better understanding of reflow behavior to obtain the optimal process.
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Fabrication and Characterization of Automotive Aspheric Camera Lens Mold based on Ultra-precision Diamond Turning Process Ji-Young Jeong, Hwan-Jin Choi, Jong Sung Park, Jong-Keun Sim, Young-Jae Kim, Eun-Ji Gwak, Doo-Sun Choi, Tae-Jin Je, Jun Sae Han Journal of the Korean Society for Precision Engineering.2024; 41(2): 101. CrossRef
Replication of Microlens Array via Partial-filling Compression Molding NamSeok Lee Journal of the Korean Society of Manufacturing Technology Engineers.2023; 32(1): 17. CrossRef
In this study, a numerical analysis for predicting the internal pressure of the flight vehicle system with relief valve and N2-injection type cooler was conducted to operate the system safely in an unsteady-state condition. By adopting an incompressible ideal gas equation to computational domain at each time step, internal pressure was calculated without iteration. To increase the accuracy of the numerical analysis results, numerical model was correlated by modifying the volume of the computational domain. To modify the volume of computational domain, internal pressure along time was compared with experimental results. It showed good agreement within system operating time. Air mass flow rate at the relief valve is calculated by interpolating the performance curve data. For accurate and rapid calculation of the internal pressure in an unsteady-state condition, time step size convergence study was conducted additionally. By using a correlated numerical model, Pcr of the relief valve is conducted to remain the flight vehicle system within an internal pressure range of 0.6-2.0 atm, in each flight profile. Finally, specific Pcr of relief valve was applied to the system and the experimental results showed that the internal pressure remained in a safe range.
This paper presents a numerical study on the thermal characteristics of a milling process of titanium alloy with nanofluid minimum-quantity lubrication (MQL). The computational fluid dynamics (CFD) approach is introduced for establishing the numerical model for the nanofluid MQL milling process, and estimated temperatures for pure MQL and for nanofluid MQL using both hexagonal boron nitride (hBN) and nanodiamond particles are compared with the temperatures measured by thermocouples in the titanium alloy workpiece. The estimated workpiece temperatures are similar to experimental ones, and the model is validated.
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