Zhigang Dong

Design and evaluation of soft abrasive grinding wheels for silicon wafers

The objective of this study is to design and evaluate soft abrasive wheels for silicon wafer grinding. In this study, CeO2, SiO2, Fe2O3 and MgO soft abrasives are used in the design of soft abrasive grinding wheels. The soft abrasive grinding wheels are then used to grind silicon wafers and compared with diamond wheel grinding and chemomechanical polishing. This study demonstrates that the newly designed soft abrasive grinding wheels are generally superior to diamond wheel grinding or chemomechanical polishing in terms of wafer surface/subsurface quality, wheel dressability, grinding ratio and material removal rate. This study further identifies the MgO soft abrasive grinding wheel as the best of the four soft abrasive grinding wheels. Discussion is provided to explore material removal mechanisms, wheel dressing characteristics and wafer surface finish and quality of the newly designed soft abrasive grinding wheels.

Topology optimization-based lightweight primary mirror design of a large-aperture space telescope

For the large-aperture space telescope, the lightweight primary mirror design with a high-quality optical surface is a critical and challenging issue. This work presents a topology optimization-based design procedure for a lightweight primary mirror and a new mirror configuration of a large-aperture space telescope is obtained through the presented design procedure. Inspired by the topology optimization method considering cast constraints, an optimization model for the configuration design of the mirror back is proposed, through which the distribution and the heights of the stiffeners on the mirror back can be optimized simultaneously. For the purpose of minimizing the optical surface deviation due to self-weight and polishing pressure loadings, the objective function is selected as to maximize the mirror structural stiffness, which can be achieved by minimizing the structural compliance. The total mass of the primary mirror is assigned as the constraint. In the application example, results of the optimized design topology for two kinds of mass constraints are presented. Executing the design procedure for specific requirements and postprocessing the topology obtained of the structure, a new mirror configuration with tree-like stiffeners and a multiple-arch back in double directions is proposed. A verification model is constructed to evaluate the design results and the finite element method is used to calculate the displacement of the mirror surface. Then the RMS deviation can be obtained after fitting the deformed surface by Zernike polynomials. The proposed mirror is compared with two classical mirrors in the optical performance, and the comparison results demonstrate the superiority of the new mirror configuration.

Surface Integrity and Removal Mechanism in Grinding Sapphire Wafers with Novel Vitrified Bond Diamond Plates

ABSTRACT In order to improve machining efficiency of sapphire wafer machining using the conventional loose abrasive process, fixed-abrasive diamond plates are investigated in this study for sapphire wafer grinding. Four vitrified bond diamond plates of different grain sizes (40 µm, 20 µm, 7 µm, and 2.5 µm) are developed and evaluated for grinding performance including surface roughness, surface topography, surface and subsurface damage, and material removal rate (MRR) of sapphire wafers. The material removal mechanisms, wafer surface finish, and quality of the diamond plates are also compared and discussed. The experiment results demonstrate that the surface material is removed in brittle mode when sapphire wafers are ground by the diamond plates with a grain size of 40 µm and 20 µm, and in ductile mode when that are ground by the diamond plates of grain sizes of 7 µm and 2.5 µm. The highest MRR value of 145.7 µm/min is acquired with the diamond plate with an abrasive size of 40 µm and the lowest surface roughness values of 3.5 nm in Ra is achieved with the 2.5 µm size.

Optimization of support location in mirror-milling of aircraft skins:

As a new technology of reducing thickness of an aircraft skin, the mirror-milling system is widely used. The objective of this study is to optimize the support location in mirror-milling of aircraft skins. The study analyzes the machining mechanisms of mirror-milling system and establishes a theoretical model to predict the milling forces. In addition, it develops a finite element model to simulate workpiece deformation so as to predict workpiece profiles in mirror-milling system. The results of the study show that with the optimized support location, the profile error of the workpiece is reduced by 73.5%, whereas machining efficiency is increased.

Design Optimization Method for Additive Manufacturing of the Primary Mirror of a Large-Aperture Space Telescope

AbstractThe lightweight design of the sandwich mirror, as a commonly used space primary mirror structure, is one of the key topics for the design of space-based optomechanical systems. Owing to the...

An Advanced Support Method of Aircraft Skin Mirror Milling - Fluid Lubricating Support

A new support method used in aircraft skin mirror milling, liquid lubricating support, is proposed in order to solve the problems of scratching aircraft skin surface caused by rolling support or sliding support. The thickness and stiffness of liquid film between skin and support head are obtained with different feed pressure. The effects of thickness and stiffness of liquid film on surface quality and dimensional uniformity of workpiece are analyzed. The surface roughness is better under the condition of liquid film. With better film stiffness, dimensional uniformity is better, and actual axial cutting depth is closer to nominal axial cutting depth.

Surface Layer Damage of Silicon Wafers Sliced by Wire Saw Process

Wire saw process is widely used in the machining of hard and brittle materials with low surface damage and high efficiency. Cutting of silicon wafers in integrated circuit (IC), semiconductor and photovoltaic solar industries is also generally using wire saw process. However, the surface layer damage induced by wire saw process will seriously decrease the wafer quality and increase the process time and production costs of the post grinding and polishing. The surface layer qualities of the silicon wafers sawed by the different wire saw processes was investigated in this paper. The characteristics of surface roughness, surface topography and subsurface damage of silicon wafers sliced by the fixed abrasive and the loose abrasive wire sawing respectively were compared and the corresponding reasons were analyzed.

Study on the Subsurface Damage of Single Crystal MgO Substrates

Single crystal MgO can be used as the substrates to deposit HTS films. The subsurface damage (SSD) generated in processing has great effect on the strength and performance of the substrates. However, the characteristics of MgO SSD and its formation mechanism have not been understood fully. In this paper, the surface and subsurface damage caused by saw cutting, rough lapping and fine lapping of MgO substrates were studied by cross-section of microscopy and SEM. The formation mechanism was discussed; and a SSD model was presented.

Comparison of Thrust Force in Ultrasonic Assisted Drilling and Conventional Drilling of Aluminum Alloy

The origin of drilling force in drilling with twist drill is quite complicated owning to the complex shape of the drill bit cutting edges. In this paper, the drilling experiments both with and without the ultrasonic were designed and conducted on aluminum alloy with pre-drilled hole. The drilling force was tested and the different effects between the cutting edges of the twist drill on the drilling force were analyzed under various drilling parameters including the spindle speed, feed rate and vibration amplitude. The drilling force of conventional drilling (CD) and ultrasonic assisted drilling (UAD) was characterized and the roles of the ultrasonic vibration in drilling were discussed.

Study on the Subsurface Damages of Glass Fiber Reinforced Composites

The machining methods such as waterjet cutting, milling, grinding, lapping, etc. are usually used to manufacture glass fiber reinforced composites (GFRCs) parts. Damages will be produced unavoidably in the machining process, no matter which machining method is employed. Subsurface damage is one of the important parameters to evaluate the surface layer damages. The detection method for the subsurface damages of glass fiber reinforced glass matrix (glass/glass) composite after machining is researched. The characteristics of subsurface damages of glass/glass composite after waterjet cutting, milling, grinding and lapping are investigated mainly, when the fiber direction is either perpendicular or parallel to the cutting surface.