Chao-Chang A. Chen

A surface topography model for automated surface finishing

Abstract This paper presents a 3-D surface topography model that has been developed to analyze and represent the spectrum of components of surface topography ranging over shape, waviness and roughness in a way suitable for generating macro- and micro-level automated surface finishing commands. Results of 3-D surface topography analysis such as comparison of desired and actual surface topography must be combinable with surface finishing processes in ways that permit the generation and output of commands, thereby causing the actual surface topography to converge towards a desired surface topography.An efficient filter, 3-D motif filter, with optimal cut-off length has been developed for roughness elements first, and then extended to waviness elements.A neutral surface shape method approximation for the machined surface shape has been proposed. Surface shape error is then eliminated as the deviation of the approximated neutral surface shape and the design surface shape.After the motif filtering, a B-spline fitting is used to represent the surface topography data within each 3-D motif cell after surface shape regeneration. The data reduction technique in 3-D motif filter methods has been shown significantly by reducing a great amount of inspection data to several elements and each element is suitable for use in surface finishing control. Some limitations of the 3-D motif filter method are discussed by the selection of different machined lay direction. The use of the developed 3-D surface topography model on automated surface finishing processes was performed on a platform constituting a 3-axis CNC machining center, inspection probe and a electrical grinder installed on the spindle housing of CNC machining center. Experimental results from an automated surface finishing system (ASFS) with in-process surface topography acquisition for mold and die finishing have shown the optimistic use of the developed surface topography model for industrial applications.

Generation of fractal toolpaths for irregular shapes of surface finishing areas

Abstract This paper presents two patterns of fractal toolpaths for irregular shapes of surface finishing areas such as a parallelogram, a trapezoid, a circle, a rhombus, an octagon, and combinations of those shapes. Surface finishing processes are used to smooth the surface form by eliminating the surface waviness left by tool marks or EDM spark erosion. Thus the surface finishing processes usually need to be performed only on several local working areas instead of global form machining. However, most of the shapes of these surface finishing areas are irregular. In this paper, fractal toolpaths have been investigated and generated for such irregular shape areas for automated surface finishing processes. A prototype CAM software has also been developed to generate the NC programs and an automated surface finishing system (ASFS) with a CNC machining center to which are attached electrical finishing tools was used to verify these fractal toolpaths. Experimental results have verified the feasibility of fractal toolpaths for different shapes of finishing areas.

Development of an automated surface finishing system (ASFS) with in-process surface topography inspection

Abstract This paper describes an automated surface finishing system (ASFS) with in-process surface topography inspection. The acquired surface topography feedback is used to calculate the surface error and to generate the finishing paths for each level of surface finishing of molds and dies. A prototype ASFS was constructed with a CNC machining center, and a laser scanning probe was used in the ASFS to acquire the surface topography data. Surface finishing of a cylindrical-shaped mold cavity was used to verify the effectiveness of the prototype ASFS. Results showed that the surface error was improved toward the specified dimensional tolerance and surface finish.

Study on numerical simulation and experiment of lightguide plate in injection molding

This paper presents the application of injection molding of wedge-shaped plates for lightguiding application. This paper discusses the influence of processing parameters on injection molding. The filling stages of lightguide plate for mold flow simulation (3D, midplane) are analyzed. The numerical simulation of mold filling process is based on the concept of control volume finite element method. The hot plastic melt touches the cold wall that forms the solid layer, a solid-liquid interface moves and a two-phase flow exists. The enthalpy model is used to predict this interface in the two-phase flow problem. The experiments carry out short-shots process to compare with numerical simulation. The experiments also indicate the pressure distribution at thin and thick ends of lightguide plate using pressure transducers. The results show that the results of 3D filling situation is close to those from experiments. The melt front progress of 3D numerical simulation is predicted more accurately than midplane numerical simulation.

Material Removal Mechanisms Involved in Rotary Ultrasonic Machining of Brittle Materials

Rotary ultrasonic machining (RUM) is considered to be a very effective and relatively accurate way to drill deep holes in brittle materials. Although brittle fracture (micro chipping) is the dominant material removal mechanism utilized by the RUM process, poor surface roughness and deep penetrated cracks are the consequence if the machining parameters are not properly controlled. To ensure the quality of the generated surface and to improve the process efficiency, efforts have been made in this study to correlate the material removal mechanisms, surface integrity and tool wear involved in the RUM process. Diamond-impregnated tools were used in the experiment and the ultrasonic vibration frequency was kept at 20 kHz. Three major material removal modes namely, impact mode, grinding mode and erosion mode were found to be the dominant removal processes at the tool tip, around the diamond wheel and around the steel sleeve respectively. It was also found that, during the grinding/erosion processes, the bonding material of the wheel was first eroded away and left big part of diamond grits well-exposed. Pull-out and/or fracture are normally the consequence of these exposed diamond grits due to the lack of support and protection.

Surface Texture Analysis of Fixed and Free Abrasive Machining of Silicon Substrates for Solar Cells

Multi-wire sawing process has been widely used for wafer slicing of silicon substrates for solar cells. Usually there are two different kinds of wire saw in multi-wire sawing process including free abrasive wire sawing with SiC grits and fixed abrasive wire sawing with diamond wire. For free abrasive wire sawing process, the material removal mechanism can be considered as lapping and the fixed abrasive wire sawing can be considered as grinding. This paper is to investigate the characteristics of the surface texture of silicon substrate fabricated by these two wire sawing process. Experimental results have been observed by white light interferometry and SEM. Some different properties of both processes have compared been with variant characteristics including 2-D and 3-D surface roughness parameters. Results of this paper can be further used to evaluate the feasibility of wire sawing process of silicon substrates for solar cells.

A Study of Two-Stage Micro Injection Compression Molding Process for Diffractive Optical Lens

This research aimed to develop a novel two-stage micro injection compression molding (μ-ICM) process for fabrication of plastic diffractive optic elements (DOE). The DOE was designed with the spherical coefficients and the Fresnel lens. A piezo actuator was installed inside the mold plate for activating the mold insert for the second compression motion for micro ICM of the DOE lens. The first experiment proceeded to find the operation window of Fresnel lens and then compare the product weight of flat spherical lens by injection molding (IM), injection compression molding (ICM) and μ-ICM. The second experiment was to investigate the effectiveness of micro compression activated by the piezo actuator by the transfer ratio of grooves (TRG) of the DOE lens with spherical lens and Fresnel lens. Results showed that the μ-ICM of the DOE can obtain the highest TRG than that of IM and conventional ICM processes. Therefore, results of this research can be explored to related aspheric optical elements with micro features, such as fine lens used in the zoom lens of camera.

Precision Measurement of Sub-50 nm Linewidth by Stitching Double-Tilt Images

In this paper we present a stitching double-tilt image method (SDTIM) to measure sub-50 nm linewidth and to evaluate the measurement uncertainty. The SDTIM employs a parallel image method using a tilt mechanism to obtain two side scans. Moreover, the stitching method is used for linewidth determination. Experiments were performed by atomic force microscopy (AFM) using an ultrasharp tip, whose radius is smaller than 5 nm. The sample rotation axis is set parallel to the top surface of the sample in order to reduce the problem of measurement position variation. Experimental results show that the developed SDTIM can be used with an uncertainty of less than 5 nm at a confidence level of 95%.

Design and fabrication of soft zoom lens

With minimization of optical-electronics devices, conventional optical zoom lens component has been explored with liquid lens and soft polymer membranes. This paper introduces a novel zoom lens system with a soft polymer material, Polydimethylsiloxane (PDMS), its shape and curvature can be controlled by pneumatic pressure. Therefore, effective focal length (EFL) of soft zoom lens (SZL) system can be controlled and altered. According to desired opto-mechanical design, this ZL has been accessed to determine the optical specifications. After the pressure activated from 0 to 0.02MPa, the change of EFL of the SZL system can reach up to 18.77% (33.44mm to 39.717mm). Experimental results show that zoom effects of the developed SZL system are significantly affected by the shape, thickness and curing parameter of PDMS soft lens. The SZL system has been verified with the function of zoom ability. Further research works on the integration of the SZL system with imaging system for mobile devices or robot vision applications.

Size effects on stylus tip reconstruction for micro and nano roughness measurement

Stylus tip reconstruction is imperative in tracing and calibration of micro and nano surface roughness measurement either for surface roughness analyzer or for scanning probe microscopy. This research is to investigate the size effects on stylus tip reconstruction in micro and nano roughness measurement. Aspect ratios within and between tips and gages, such as Tip Aspect Ratio (TAR) of tip width to height, Gage Aspect Ratio (GAR), Height Aspect Ratio (HAR) of tip height to gage height, and Width Aspect Ratio (WAR) have been formulated to develop a stylus tip reconstruction method (STRM) to estimate tip profile from the measured profile image and the traced gage profile. A simulated program has been used to test the developed STRM with different aspect ratios of tips and gages. Experiments have been conducted on a Hommelwerke T4000 surface roughness analyzer with a TKL T100 tip of radius 5 μm and a Veeco Dektak 200 surface roughness analyzer with nominal radius values of stylus tip radius 12.5 μm to measure a traced roughness gage (Mitutoyo Serial No. 0300042) of step height of 10 μm and razor blade in ISO 5436 standard. Experimental results show that the difference of STRM on step gage and razor blade measurement is about 4 % and the developed STRM can be further used to estimate the geometric size effects of tip reconstruction in scanning probe microscopy (SPM).