Materials Science Forum Vols. 532-533

Abstract: Nowadays faceted reflector design has become popular in automotive illumination systems. The advantage of a compound surface enables it to achieve the required hot spot intensity by directing more than 60% of the generated light towards the road, thereby largely illuminate the area through the aperture. The research is oriented to fabricating the mold insert on ultra-precision raster milling (Freeform 705G). In this paper, the tool path generation method for automotive headlamp reflectors is studied, and a practical gouging detection and avoidance algorithm is proposed. The surface roughness and form accuracy (peak-to-valley height) are then calculated theoretically using mathematical formulae. Through the tool path generation of a small but representative surface patch with a gap, a possible way is finally found to generate the tool path for such a class of freeform surface with special equipment.

Abstract: A new class of 4-DOF Parallel Manipulator (PM) with five supporting subchains is synthesized based on enumeration method. Targeting at 4PUS-1PPU PM, the inverse kinematics and dexterity analysis are developed, and the geometric parameters are determined.

Abstract: Micro/nano handling is an important enabling technology for future manufacturing. In the micro scale, adhesion is a severe problem for efficient and accurate handling tasks. The cause of the adhesion is largely from the microforces, namely van der Waals, electrostatic and capillary forces. Those forces, however, are functions of ambient environmental conditions. This paper exams two important ambient environment parameters in normal micro/nano handling environment: temperature and humidity, in both theoretical analysis and experimental studies. A short guideline for microhandling with temperature and humidity consideration is suggested based on the studies.

Abstract: In this paper, a new method to fabricate various microstructures on thermoplastics by soft lithography is demonstrated. Varied line width and varied line depth microstructures that are frequently used in micro optical products, are obtained by micromolding with simple pattern stamps. This has not been reported previously. In the new method, the variations of the line widths and depths can be adjusted by changing the side shape and the curvature of the stamp. Factors, such as temperature, pressure and the degree of crystallinity on the product qualities are analyzed. Results show that besides suitable temperature and pressure, which are important for obtaining consistent microstructures; lower crystallinity can also help for better product qualities. Optical, SEM and AFM analyses show the new method can fabricate varied line width and varies line depth microstructures with desired accuracy and features. The method proposed in this work may find potential applications in producing micro products in areas such as sensors, biochips and non-linear optical devices.

Abstract: Microlens arrays are widely used as critical components in a large number of photonics and telecommunication products. The increasing demand for high-tech products provides an expanding room for the development of the micro-fabrication technology. This study presents a tool compensation for correcting the form error of fabricated microlenses in ultra-precision machining with fast-tool-servo (FTS) system. After presentation of optimal cutting conditions deduced on the basis of cutting experiments of microlens arrays, a tool radius compensation method will be proposed and evaluated in this paper. This methodology makes use of form measurement data from a Form Talysurf system to modify the C program employed in the software of ultra-precision machining FTS system – SOP. The form error was successfully reduced after implementation of tool compensation.

Abstract: An investigation into a Digital Manufacturing and Testing Procedure (DMTP) for freeform optics is presented in this paper. The paper studies the characteristics of the DMTP which are of special use in ultra-precision machining (UPM) of freeform optics, i.e. the construction of a model of DMTP, the construction of a digital prototype of an optical system, a Digital Testing (DT) system for image quality, digital testing and simulation of the optical image quality.

Abstract: The influence of materials swelling across the steps on surface roughness under up-cutting and down-cutting direction in ultra-precision raster milling was investigated. The normalized extent of swelling is characterized by a swelling significance index, defined based on the power spectral density of the roughness profile. Materials swelling was found to be significant in ultra-precision raster milling, especially when copper alloys machined in the up-cutting direction. The findings in the present study provide an important means for improving the surface finish of the raster-milled surfaces and optimizing the cutting conditions.

Abstract: The thixoforming of wrought magnesium alloy was analyzed with computer numerical simulation based on rigid plastic/rigid viscoplastic finite element method. The simulated parameters were chosen and depended on the constitutive model of semi-solid AZ61 alloy that was established using the multiple nonlinear regression method in our prior literature. Thixo mechanical properties of semi-solid AZ61 alloy in high solid volume fraction were also analyzed. Behaviors of metal flow and temperature field were obtained, which were also compared with experimental data in literature. Research showed that the hard deformation magnesium alloy had great filling ability in semi-solid state, and the stress and strain distributions in workpiece after thixoforming were uniform. The semi-solid thixoforming technology has taken priority of the traditional processing.

Abstract: Nowadays, the topology optimization method is extensively adopted for the design of material microstructures to achieve desired behaviors. The present work is concerned with the optimal design of the stiffness and thermal conductivity of 3D microstructure unit cells with the specific material volume fraction in conjunction with the homogenization method and the finite element method. Numerical examples are given to demonstrate that optimal material layouts are successfully achieved and the initial layout has a great effect on the optimal microstructure.