Papers by Author: You Min Huang

Abstract: An analytical thin film thickness model based on the geometry of a commercial vacuum coating system is proposed. This model can calculate the profiles of linear variable filters (LVFs), which are used to eliminate overlapping orders of spectra due to the use of a diffraction grating and which are fabricated using a local mask, producing a linearly variable thickness. While the filter transmits the first-order wavelength and blocks the second-order wavelength. The 75% and 25% relative thicknesses deviation between the evaporated film and the theoretical model is less than 5%, indicating good suitability for LVF design and fabrication.

Abstract: During robotic assembly and interactive applications, the robot end-effector must follow a motion trajectory and exert an appropriate force profile against the contacted environment to provide a specified dynamic working compliance. It is a difficult control problem. Here, an embedded robotic control structure is constructed and the related hybrid control software programs are developed. The model-free intelligent fuzzy sliding mode controller is introduced to design force and position controllers, respectively for hybrid impedance control purpose. The experimental results are provided to demonstrate the effectiveness of the proposed hybrid impedance control system.

Abstract: There has been a significant research interest in metal micro-forming for the last ten years. However, neither a methodology nor an exact micro mechanical property has been well determined. Hence, several experiments are carried out in this research to point out the influence of “size effect”. Based on the comparison between the experimental data and relevant parameters, the material characteristics in micro scale can be found. In order to find the mechanical properties in micro scale, this study shows the effect of specimen size and grain size on the micro tensile test of copper material. Firstly, five copper micro-sheets with different thicknesses have been chosen as experimental materials. Since the minimum standard test piece formulated in ASTM is still too big for this micro tensile test, this study decided to shrink the sample size of specimen shape to 1/2 . Then the flow stress decreases with decreasing specimen size. This way is able to get the important factor which influence the flow stress on the micro tensile test. Secondly, these samples of different grain sizes are made by heat treatment. Then these samples of different grain sizes are used to conduct the experiment. According to the experimental result, the change of flow stress, which is influenced by various grain sizes, can be found. Finally, the change in the mechanical behavior between specimen size and grain size is obtained.

Abstract: A methodology of formulating an incremental elasto-plastic three-dimensional finite element model, which is based on Prandtl-Reuss flow rule and von Mises’s yield criterion respectively, associated with an updated Lagrangian formulation, is developed to simulate elliptical cup drawing process. An extended algorithm is proposed to formulate the boundary conditions, such as the yield of element, maximum allowable strain increment, maximum allowable rotation increment, maximum allowable equivalent stress increment, and tolerance for nodes getting out of contact with tool. In order to verify the reliability and accuracy of the FEM code, the fractured thickness of a specimen in the simple tension test is adopted as the fracture criterion of forming limit in simulation. A set of tools was designed to perform the elliptical cup drawing experiment on the hydraulic forming machine. According to the simulation and experimental results, the limit drawing ratio (LDR) amounts to about 2.136 for penetration in the elliptical cup drawing process of this study. This paper also found a comparison of the LDR of different tool radii. According to the definition of LDR, when the die radius is increased from R3.0mm to R9.0mm, the LDR would increase from 2.11 to 2.157. When the punch radius is increased from r3.0mm to r9.0mm, the LDR would increase from 2.07 to 2.181. This paper has provided a better understanding of the elliptical cup drawing process for improving the manufacturing processes and the design of tools.

Abstract: A methodology of formulating an elasto-plastic three-dimensional finite element model, which is based on Prandtl-Reuss flow rule and von Mises yield criterion respectively, associated with an updated Lagrangian formulation. An extended r-min algorithm is proposed to formulate the boundary conditions, such as the yield of element, maximum allowable strain increment, maximum allowable rotation increment, maximum allowable equivalent stress increment, and tolerance for nodes getting out of contact with tool. In order to verify the reliability and accuracy of the FEM code, the fractured thickness of a specimen in the simple tension test is adopted as the fracture criterion of forming limit in simulation. A set of tools was designed to perform the elliptical cup drawing experiment on the hydraulic forming machine. According to the simulation and experimental results, the minimum thickness is concentrated on the contact regions between work-piece and punch major axis, because the camber radius is relatively large along the minor axis, the ones that bear are relatively small to the circular tensile stress, so the thickness does not change much. The limit drawing ratio (LDR) amounts to about 2.136 for penetration in the elliptical cup drawing process of this study. According to the definition of LDR, when the die radius is increased from R3.0mm to R9.0mm, the LDR would increase from 2.11 to 2.157. When the punch radius is increased from r3.0mm to r9.0mm, the LDR would increase from 2.07 to 2.181. This paper has provided a better understanding of the elliptical cup drawing process for improving the manufacturing processes and the design of tools.

Abstract: This study aims to clarify the process conditions of the UO-tube of a sheet metal of steel. It provides a model that predicts not only the correct punch load for drawing, but also the precise final shape of products after unloading, based on the tensile properties of the material and the geometry of the tools used. An elasto-plastic incremental finite-element computer code, based on an updated Lagrangian formulation, was developed to simulate the UO-tube process of sheet metal; the results are compared with corresponding experimental results. Special care was taken to formulate accurate boundary conditions of penetration, separation and alternation of the sliding-sticking state of friction, as the contact conditions between the tools and the sheet varied throughout the entire processes of U-bending and successive O-bending. Calculated sheet geometries and forming force agree well with experimental data. In particular, selective reduced integration was adopted to formulate the stiffness matrix. The extended r-minimum technique was used to deal with the elasto-plastic state and contact problems at the tool-metal interface. A series of simulations were performed to validate the formulation in the theory, leading to the development of the computer codes. The whole deformation history, the distribution of stress and the distribution of strain during the forming process were obtained by carefully considering the moving boundary condition in the finite-element method. The simulation demonstrates clearly the efficiency of the code to simulate various bending processes that proceed under complicated deformation- and contact-history.

Abstract: In this study, a general simulation code is developed to analyze the shrinkage effect of polymerization and optimize the fabrication parameters including the scanning path, exposure time and scanning speed for the stereolithography system. The code is based on the dynamic finite element method. Liquid element is preconstructed without curing properties till the absorption energy exceeds the critical value of dynamic stiffness matrix assembling. A unit element block is utilized with a weight coefficient for expressing a laser Gaussian energy distribution during the discretizing of the scanning path into increments. A fan blade is proposed to validate the agreement between the simulation and experimental results. The prototype is a fabrication and the surface of blade was measured by the digitizing system ATOS (Advanced TOpometric Sensor) for comparing the deformation with analysis prediction. Consequently, the simulated result closely conforms to the experimental result.

Abstract: This study aims to clarify the process conditions of the hat-type drawing of a sheet metal of steel. It provides a model that predicts not only the correct punch load for drawing, but also the precise final shape of products after unloading, based on the tensile properties of the material and the geometry of the tools used. An elasto-plastic incremental finite-element computer code, based on an updated Lagrangian formulation, was developed to simulate the hat-type drawing of sheet metal. In particular, selective reduced integration was adopted to formulate the stiffness matrix. The extended r-minimum technique was used to deal with the elasto-plastic state and contact problems at the tool-metal interface. A series of simulations were performed to validate the formulation in the theory, leading to the development of the computer codes. The whole deformation history and the distribution of stress and strain during the forming process were obtained by carefully considering the moving boundary condition in the finite-element method. Results in this study clearly demonstrated that the computer code for simulating the hat-type drawing process was efficient.