As products life cycles are becoming shorter, the reduction of die and mold manufacturing cost and time is becoming more crucial in the machinery, automotive, and electronics industries. Over the past decades, many initiatives have been made to develop high performance free-machining steels without significant degradation of mechanical properties. To develop a modified AISI P20 free-machining steel, we studied the effects of B, N, and S additives on the variations of the cutting forces and metal structures such as grain size, density, and distribution of free-machining inclusions. From a set of experiments, it was observed that an appropriate addition of B and N additives reduces the resulting cutting force by approximately 6.3% and delays the tool wear progress. During the solidification B and N additives form hBN precipitates, with a layered and planar structure, within the steel matrix. The hBN precipitates’ weak shear strength results in lowering the required milling force. It is also confirmed that machinability is prominently improved when a large number of microsized hBN precipitates are distributed uniformly in the steel matrix. This study could contribute to the development of high performance BN-added free-machining steels for die and mold applications.
A spectral-domain interferometer with dual reference paths and orthogonal polarization states to avoid measurement errors when interference signals overlap is proposed and realized. In our previous study, by using dual reference mirrors, two inherent problems of the spectral-domain interferometer, the non-measurable range and the directional ambiguity problem, were successfully solved. However, because of the overlap of interference signals, the absolute distance values were distorted. In this study, the polarization states of beams from two reference paths were made orthogonal to eliminate the interference signal between them, so that the overlap can be essentially avoided. First, we performed a numerical simulation on the measurement error with respect to the degree of superposition of the interference signals. Simulation results show that with the previous method the measurement error can be up to approximately 1 μm within the overlap region, but the proposed method drastically reduced this error to below 100 nm. Then, the proposed method was experimentally realized and verified. In conclusion, the proposed method can measure the absolute distances without the inherent problems as well as the measure errors caused by the overlap of the interference signals.
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Sub-100-nm precision distance measurement by means of all-fiber photonic microwave mixing Yoon-Soo Jang, Jungjae Park, Jonghan Jin Optics Express.2021; 29(8): 12229. CrossRef
The purpose of this study was to suggest the method for automated locomotion modes (Level Walking, Stair Ascent, Stair Descent) detection based on the Radial Basis Function Support Vector Machine (RBF-SVM) for the hip gait assist robot. The universal hip gait assist robot had a limit in detection of the walking intention of users because of the limited sensors’ quantity. Through the offline training, using MATLAB, we trained the collected gait data of users wearing the hip gait assist robot and obtained the parameter of the RBF-SVM model. In the online test, using LabVIEW, we developed the algorithm for the locomotion modes decision of individuals using the optimized parameter of the RBF-SVM. Finally, we executed the gait test for three terrains through the walking environment’s test platform. As a result, the locomotion modes decision rate for three terrains was 98.5%, 99%, and 98% respectively. And the decision delay time of algorithm was 0.03 s, 0.03 s, and 0.06 s respectively.
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The study focused on the development of the CAM system restricted to the fabrication of variable pitch screws by using turning centers. To develop the dedicated CAM system at a low cost, open source programming language was used as much as possible. A commercially available 3D-CAD system was used to model variable pitch screws. The edge data of the variable pitch screw was extracted from 3D-CAD data of the variable pitch screw, and then a number of the edge data were copied by the amount of feed in the longitudinal direction of the screw to make a cutter path. The successive cutter path was repeatedly generated by reducing the size of the edge data. The advantage of this method of generating the cutter path is very simple and easy to use, compared with the conventional CAM systems. During the cutter path generation, the system can detect the collision between the cutting tool and the workpiece. As a result, the validity of the developed CAM system for variable pitch screws fabrication was confirmed from several examples of the cutter path generation.
The purpose of this study was to investigate the springback behavior of magnesium alloy (AZ31B) at high temperature with respect to the holding time in the die-set. The changes of microstructure in the springback during V-Bending were analyzed. The springback of the magnesium alloy sheet showed a tendency to decrease as the forming temperature and the retention time in the die increase. In the microstructure analysis, there was minimal change in the microstructure at room temperature, while at high temperature the microstructure changed markedly. The increasing material holding time in die has been shown to reduce springback from internal energy reduction because of recrystallization and grain growth at high temperature.
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Analysis of acoustic emission signals during bending deformation of magnesium alloy sheet Jae-Hyeong Yu, In-Gyu Choi, Jung-Sik Yoon, John S. Kang, Wan-Jin Chung, Chang-Whan Lee Nondestructive Testing and Evaluation.2025; : 1. CrossRef
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When a building is detonated, the debris generated collides with the ground with very high energy and bounces back. This phenomenon is called ricochet. Ricochet increases risk by increasing the moving distance of the debris. The ricochet of debris is affected by the shape of the debris. In this paper, the behavior and moving distance of debris along the shape of debris were studied. For various initial conditions, the ricochet of debris was studied through the FEM, and the results were fitted to a 3D curved surface to predict the speed and angle after the ricochet. The moving distance of the debris was calculated using the trajectory formula considering the drag coefficient using the MATLAB. The ricochet of debris is affected by the contact area with the medium. As the contact area increases, the reflection angle increases because of the increase of the repulsive force. As the size of the debris increases, the energy loss also increases because of the increasing of the contact area. Thus, the moving distance of the cylinder debris is shorter than that of the sphere debris.
In CNC machining, NC data created by CAM software is usually linearly interpolated. This linearly interpolated tool path, however, may degrade the dynamic motion performance of the machine tool and the geometric accuracy in comparison with the reference CAD data. Tool path smoothing can be an effective way to address these problems. In this paper, a five-axis tool path smoothing method is proposed based on dual cubic B-spline curves. The proposed smoothing method includes two steps. First, the tool orientation is adjusted to reduce drastic changes in tool orientation movement. Then, dual B-spline curves are generated for smooth interpolation of tool position and orientation, wherein their control points are created by using modified internal division points between the top and bottom points of the tool defined by given tool position and orientation vectors. The B-spline curves pass through the junctions of straight line segments comprising the top and bottom points, respectively. Smooth tool position and orientation vectors are finally obtained by simultaneous interpolation of the B-spline curves. The proposed method is implemented in a PC-based five-axis control system and experimentally demonstrated to show improvements in the dynamic motion performance and the geometric accuracy compared with the conventional linear interpolation.
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Research on three-section type tool path planning algorithm for tooth hot pressing model cutting Lijun Zhang, Shaowei Fang, Jiayi Xu, Ning Yang, Weijian Guo, Hang Wang, Changliang Li Computers & Industrial Engineering.2022; 163: 107817. CrossRef
For esthetic and functional implant prosthesis, the retention type of implant should be selected considering the oral condition of the patient. However, studies on the differences in biomechanical stability of the retention type are scarce. The purpose of this study was to evaluate the biomechanical effects between retention types in implant prosthesis using 3- dimensional finite element analysis. Two retention types (Cement and Screw-Cement) were considered for the implant complex consisting of the ComOcta abutment, SS type implant, and screw all implanted in the mandibular segment of the bone block. Static finite element analysis was performed under external loads of 200 N (Vertical Load) and 100 N (Oblique Load) to each cusp tip. We measured the von-Mises stress fields in abutment and implant, and the principal strain distribution of the mandibular bone to evaluate the risk of fatigue failure in the bone. Separations between the implant components were also evaluated. The results show that with the ComOcta abutment Cement type provided enhanced stability.
The necessity for printing multi-materials has increased as the importance of 3D printing grew in various industries. Many studies have undertaken for printing multi-materials simultaneously. In ME (Material Extrusion) type 3D printers, the method of printing different materials using multi nozzles is generally commercialized. Polymers with different composition are hardto-mix with each other, making it difficult to maintain the structural strength of printer parts. So the MJ type 3D printer uses a unique method that mixes multi-materials in a liquid state before printing. In the ME type 3D printer, there were also efforts to mix materials in a melted state, but they were mainly demonstrated for multi-colored parts. In this study, the effect of multi-material mixing on structural strength changes was tested. Multi-Materials were printed with the ME type 3D printer by using one nozzle with a multiple filament feeding system. The bending and tensile tests were conducted to verify the structural characteristics.
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Analysis of Correlation between FDM Additive and Finishing Process Conditions in FDM Additive-Finishing Integrated Process for the Improved Surface Quality of FDM Prints Ji Won Yu, Hyung Jin Jeong, Jae Hyung Park, Dong Hun Lee Journal of the Korean Society for Precision Engineering.2022; 39(2): 159. CrossRef
Study on the Reduction of Food Fabrication Time in Additive Manufacturing Process Using Dual Nozzle Seung Yeop Baik, Ju Ho Park, Sang In Kang, In Hwan Lee Journal of the Korean Society for Precision Engineering.2021; 38(11): 879. CrossRef
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