Key Engineering Materials Vols. 364-366

Abstract: In this study, the finite element method was used to investigate the cold elliptic-shaped flaring process of metal tubes with a conical punch from a tube billet. A series of simulations on tube flaring was carried out using the FEM program DEFORM 3D. The influence of process parameters such as tube wall thickness, punch conical length, aspect ratio of elliptic shape, friction factor, punch fillet radius and strength coefficient of the billet material on the critical flaring ratio of the tube were analyzed.

Abstract: Proximity printing is one of the lithographic processes used in fabricating semiconductor, micro optoelectronic components and micro electro-mechanical systems to transfer mask pattern to the substrate. This research investigates the cause of pattern distortion based on the analysis of diffraction effect of light beam due to the gap between the mask and the photo resistant in the proximity printing process. The Huygens-Fresnel diffraction theorem is first employed to derive the diffraction effect. It shows that irradiance decreases as the gap increased, which is consistent with practice. Further investigation shows that shading area can be exposed, even with a small gap, due to the diffraction effect that makes the exposed image imprecise. A deeper analysis on the diffraction effect in microlithography of proximity printing with single-aperture, dual-aperture, and multi-aperture masks is investigated. It shows that the contrast irradiance between the exposed and the shading regions becomes closer as the gap increases. This makes the boundary of image become vague and causes the exposed image to be distorted. Experiments are then designed and conducted to verify the derived results. Experimental results using φ80μm circular single-, dual- and multiaperture masks showed that the boundary of adjacent circular apertures begins to crossover with each other when the gap reaches 240μm. When the gap increases to 360μm, interference between adjacent circular apertures becomes stronger that results in hexagonal images. This shows that experimental results are consistent with simulations from theoretical analyses. The main contribution of this research is to analytically find the distortion of image in proximity printing due to diffraction effect and to verify the theory by experiments.

Abstract: This paper proposes a novel wheel-shaped grinding/polishing tool, which is designed to be controlled on both the self-rotation around its axis and the co-rotation around vertical axis Z at the specified speeds respectively. Therefore, the surface material of the workpiece can be removed by virtue of self-rotating motion. On the other hand, the co-rotating motion will also change the manufacturing orbit continually. To analyze the characteristics of the tool, material removal in the manufacturing zone on the workpiece surface is first established through theoretical modeling. Subsequently, a good evaluating method, i.e. power spectral density, for analyzing the frequency spectrum features of material removal function in computer-controlled optical grinding and polishing is introduced in detail. By simulation, the power spectral density of the material removal function was cut into several parts, some frequency with low amplifies of material removal function were removed, and the modified material removal function reflected the actual processing status, which was helpful in removing some residual high frequency errors on the surface of the workpiece. Finally, the high amplitude such as at high frequency of 110mm-1 and 210mm-1 was reserved and some other low amplitude frequencies were removed.

Abstract: The influences of ultrasonic field to polishing performance of Polishing Based on Coupling Vibration of Liquid (PCVL) are analyzed here. The simulation results shows that sound field in the original polishing device is rather uneven due to the existence of standing wave. To obtain better polishing performance, the experimental equipment was modified. Uniformity of the sound field was improved by preventing standing wave, thus a better surface quality could be achieved. Furthermore, a higher machining efficiency could be also obtained because sound intensity was strengthened at the same time. From the results serials of experiments, the improvements made by modified equipment are clearly shown.

Abstract: Due to the light weight and electromagnetic interference shielding capabilities in magnesium alloy material, it is widely utilized in 3C electronic components and automobile parts. However, its formability is very poor due to the phenomenon of negative strain hardening rate appearing as the deformation in large strain range, so it is usually formed as die casting or casting styles leads to much scrap, and manufacturing cost is thus increased. The objective of this study is to investigate the effect of process parameters on T-shape tube hydro-forming characteristics for magnesium alloy and it may offer the data resulting from the analysis to predict an acceptable product of tube fitting for magnesium alloy forming in industry. AZ31 magnesium alloy tube is used as the billet material for hydro-forming with hydraulic pressure as the main forming power combined with the mechanical auxiliary force from the punch to fabricate the T-shape tubing products. Finite element code DEFORM-3D is adopted to investigate the forming states of T-shape tube forming, by changing process parameters; such as punch velocity, hydraulic pressure, fillet radius of the die and tool-workpiece interface friction etc. to investigate the material flow of tube fitting, wall thickness variations, and stress and strain distributions. By qualifying the forming processes whether if it is completed or not, and synthesizing the overall analysis and judgment, we establish an admissible level of process parameter range for complete tube manufacture. The results show that suitable mechanical force can help material flow, prevent large strain deformation falling into the area of negative strain hardening rate, enhance magnesium alloy to become easy in forming and make tube fitting to be formed successfully.

Abstract: In the deep drawing of cups, the earing defect is caused primarily by planar anisotropy in the sheet. In order to obtain the optimal products in deep drawing process, blank shape is a very important formability factor. In this study, the finite element method was used to investigate the cup height and forming force of the cylindrical cup drawing process. A finite element analysis was also utilized to acquire the designed profile of the drawn products, a reverse forming method for obtaining the initial blank’s shape according to the forward cylindrical cup drawing simulation is proposed. The design of initial blank’s shape is also confirmed to obtain the designed profile of drawn cups. The influences of the blank’s shape on the height of product, the forming force, the effective stress and the effective strain were also examined.

Abstract: Ultra-precision raster milling is one of the most significant techniques for the fabrication of high precision components with the surface roughness less than 10nm and form errors less than 0.2 um, without the need for any subsequent polishing. However, no matter how well a machine may be designed, there is a limit to the accuracy that can be achieved. This paper studies the machining errors caused by the diamond tool and the axis motions using Freeform 705G. With an empirical approach, the error sources are separated based on their effects on the surface finish. The main source leading to poor surface finish is identified. This establishes a basis for subsequent error compensation and equipment maintenance.

Abstract: In this reaearch, the finite element method is used to investigate the steady-state wire drawing process for strain-rate sensitivity materials. A series of simulations on the wire drawing using the program DEFORM-2D were carried out. The influences of the process parameters such as drawing speed and strain-rate sensitivity index of the wire material on the drawing die stress, the separation force, the effective strain-rate distribution, and the effective stress distribution of the drawing die were examined.

Abstract: Optical fiber sensors have been developed during the past decade to measure a wide range of physical quantities such as strain and temperature. The perturbation of the surrounding field in the host due to the presence of the optical sensor will not only alter the values of the field variables being measured, but may also affect the integrity of the host. Resulting degradations can compromise the accuracy and long term reliability of the smart structure. The present paper focuses the attention on constitutent interaction between the optical fiber, coating, matrix and host material. An analytical model to predict the stress fields in the vicinity of the embedded optical fiber was derived. The theoretical development was based on the four concentric cylinders models which represented the optical fiber, protective coating, matrix and host material, respectively. The interfaces between each constitutent were assumed to be perfect bonds, so that the tractions and displacements were continuous across each interface. In this investigation, the host structure was subjected to three normal loadings along the axial directions. Numerical examples were presented to investigate the effects of the coating and host material on the stress distribution in the vicinity of the embedded optical fiber.

Abstract: This study has developed a thermal model for laser-assisted cutting of zirconia ceramics. Laser-assisted cutting can increase ceramics removal rates by utilizing a localized heat source to elevate the workpiece temperature prior to material removal with traditional cutting tool. At high temperatures the yield strength of ceramics can decrease below the fracture strength, changing the material deformation behavior from brittle to ductile and enabling the use of a single point cutting tool to remove material at rates approaching those of metal cutting. A thermal model has been developed for the workpiece of ceramics cylinder rotating with a constant speed, which was preheated by a laser and cut by cutting tool. Since the cutting tool followed the moving laser with a fixed distance in the axial direction, i.e. the feed rate of the cutting tool was the same as the moving velocity of the laser, this thermal model has been formulated in a cylindrical coordinate system that moved with the laser beam or cutting tool and therefore, this problem was a quasi-steady-state problem. An analytical solution for this thermal model has been obtained. The results calculated by this model agree with the available experimental data. The temperature field is presented during laser-assisted cutting of ceramics. The effects of feed rate and laser power on temperature field are also discussed in this study.