Advanced Materials Research Vol. 1017

Abstract: Single Pointe Diamond Turning (SPDT) of silicon can be an extremely abrasive process due to the hardness of this material. In this research SPDT is coupled with the micro-laser assisted machining (μ-LAM) technique to machine an unpolished single crystal silicon (Si) wafer. Si is increasingly being used for industrial applications as it is hard, strong, inert, light weight and has great optical and electrical properties. Manufacturing this material without causing surface and subsurface damage is extremely challenging due to its high hardness, brittle characteristics and poor machinability. However, ductile regime machining of Si is possible due to the high pressure phase transformation (HPPT) occurring in the material caused by the high compressive and shear stresses induced by the single point diamond tool tip. The μ-LAM system is used to preferentially heat and thermally soften the workpiece material in contact with a diamond cutting tool. Different outputs such as surface roughness (Ra, Rz) and depth of cuts (DoC) for different set of experiments with and without laser were analyzed. Results show that an unpolished surface of a Si wafer can be machined in two passes to get a very good surface finish.

Abstract: Micro-machining of hard dies and molds for optical parts or precision instruments is required to extend die and mold life. This paper investigates the effect of cutting fluid on diamond tool life under micro V-groove turning of cobalt-free tungsten carbide. Zinc dialkyldithiophosphate fluid (ZnDTP) displayed excellent diamond tool wear resistance in previous experiments. The performance of this cutting fluid is compared to newly developed vegetable oil based cutting fluid with dispersed MoS₂ nanotubes. This paper investigates nanopolycrystalline diamond (NPD) tool life with a rake angle of 0° and-30° under continuous micro V-groove turning (i.e. face turning), of cobalt-free tungsten carbide using the developed cutting fluids. Superior diamond tool edge wear resistance is observed when using the dispersed MoS₂ nanotubes in vegetable oil and using a NPD tool with a-30° rake angle.

Abstract: Conventional characterization methods of grinding surface using surface roughness parameters, e.g., Ra, depend on either the resolution of the measuring instrument or the length of the sample. But fractal dimension (FD) as a scale-independent fractal parameter is effective to evaluate the ground surface at any length scale and represent lots of surface phenomenon at its relevant length scales. In this paper, a three-dimensional (3D) box-counting fractal analysis method is used to investigate ground surface morphology of monocrystal sapphire by calculating 3D fractal dimension of the ground surface. The results obtained show that fractal dimension decreases with the increasing surface roughness. For the ground surface with higher fractal dimension, its microtopography is more exquisite with minor defects. Once the fractal dimension become smaller, deep cracks and pronounced defects are exhibited in ground surface. Moreover, the ground surface obtained in ductile mode has much higher fractal dimension than that in brittle mode. Therefore, the fractal analysis method has the potential to reveal the ground surface characteristics of monocrystal sapphire.

Abstract: Lasers have the potential for the micromachining of germanium (Ge). However, the thermal damages associated with the laser machining process need to be properly controlled. To minimize the thermal damages, a hybrid laser-waterjet ablation technology has recently been developed for micromachining. This paper presents an experimental study to assess the machining performances in microgrooving of Ge by using a nanosecond laser and the hybrid laser-waterjet technology. The effects of laser pulse energy, pulse overlap and focal plane position on the groove geometry and heat affected zone (HAZ) size are analyzed and discussed. It is shown that the hybrid laser-waterjet technology can give rise to narrow and deep microgrooves with minimum HAZ.

Abstract: Abrasive waterjet machining (AWJ) is one of the fastest growing non-conventional machining methods. However, low pressure and fine abrasive implemented in AWJ precision machining for reducing the surface damage reduce the efficiency. Therefore ultrasonic vibration is considered to apply on the workpiece to improve the machining efficiency. In order to analyze the effect of the vibration on erosion in AWJ machining, smoothed particle hydrodynamics (SPH) is used to simulate the erosion process for avoiding the mesh distortion in finite element method (FEM) when simulating large deformation and high strain rate problems. The results show that the application of ultrasonic vibration can effectively improve the erosion rate due to the dynamics variation of the erosion process.

Abstract: The micro patterning on a cylindrical surface is conventionally carried out by electrochemical machining, chemical etching, cutting and so on. However, there exists some problems in machining dimensional errors and tool lives. On the other hand, blasting is expected as one of micro fabrication methods and progresses to apply for machining of hard and brittle materials. The purpose of this study is to develop the micro blasting technique for patterning of micro herring-bone grooves on spindle surfaces of the fluid dynamic bearings. Then, machining characteristics in blasting of rotating workpieces are experimentally investigated, analyzing stock removals, burr heights and groove shapes. In addition, micro herring-bone grooves are patterned on spindle surfaces by blasting and the performance of herring-bone bearings are evaluated. The herring-bone bearings with micro grooves patterned on a spindle surface by blasting have enough performance, compared with conventional ones.

Abstract: Based on "indentation fracture mechanics" model, this paper offers a model on the crack depth of surface in ceramics grinding. Through carrying out one-way trip grinding and surface crack depth measuring experiments on silicon nitride, a model for silicon nitride grinding surface crack depth is established. In this model, the parameters can be confirmed by the experiment. By the grinding experiment, the parameters of the model can be confirmed, and the controlled grinding surface quality for the ceramic materials can be expected.

Abstract: Engineering ceramics have received significant attention in the recent years owing to their exceptional mechanical properties, which are expected to be beneficial for engineering applications. However, it has always been a great challenge to realize ductile-mode grinding in engineering ceramics, with one of the critical obstacles being the heat generation that limits the removal rate. As a result, thermal damages are often observed on the ground surfaces. This paper presents the ductile-mode grinding. In the process the grinding wheel is excited along the radial direction by applying an ultrasonic vibration of frequency is 38.5 kHz and amplitude of 0-2 μm. The wheel comes in contact with the Al₂O₃ ceramic at constant forces 18-24 N. Experimental results indicate that the ground surface is devoid of thermal damages, when removal rate of the vibration-assisted process is approximately 1.5 times higher than without vibration.Keywords: ductile-mode grinding, radial directional vibration, hard and brittle material, engineering ceramic, thermal damage

Abstract: Quartz fiber reinforced ceramic matrix composites have poor thermal conductivity yet high fiber hardness that make them difficult for machining. Especially for drilling of blind hole, the cutting heat can not be conducted away from the semi-enclosed hole quickly, which may result in serious tool abrasion and poor machined quality. Experimental research on helical milling process was carried out, specifically on the machining of Φ8mm blind hole. Exploiting grinding mechanism, self-developed electroplated diamond trepanning tool was used. The experimental results show that the helical milling method exhibit advantages e.g. reducing cutting force, improving cutting heat dissipation and achieving good hole quality.

Abstract: Abrasive water jet machining is considered as a promising technique in hard and brittle material processing. This paper studies the erosion performance of the alumina ceramics in the different process parameters. In the erosion experiments, alumina ceramics wafers were eroded by the abrasive waterjet machining. The single factor experiments were carried out to understand the effect of different process parameters (jet impact angle, standoff distance, water pressure, abrasive particle diameter) on the material removal rate (MRR), the removal depth and surface roughness (Ra). The experimental results can provide guidance for alumina ceramics abrasive water jet cutting and polishing.