Papers by Author: Jun Wang

Abstract: Micro/nanofabrication with less damage has been raised as a challenging issue in advanced micro/nanomanufacturing industries. Recently, a new hybrid laser-waterjet machining technology has been developed, in which material is removed by laser heating and softening and waterjet cooling and expelling with negligible thermal damage to the workpiece. An optimization of the process parameters, such as laser pulse energy, laser pulse overlap, focal plane position, and waterjet offset distance, in the machining of silicon using this hybrid technology is presented in this study. Grey relational analysis based on an orthogonal array is employed to optimize the multi-performance characteristics, where the groove width and heat-affected zone are minimized while the groove depth is maximized.

Abstract: Three kinds of Al2O3 ceramics matrix composites, such as Al2O3-TiB2, Al2O3-SiC and Al2O3-TiC, were prepared by two steps, which were synthesis of the composites by thermal explosion under a pressure of 20MPa and hot pressing of the composites at 1700°C under a pressure of 32MPa respectively. The preparation process, the composition and the microstructure of the composites were investigated in detail. The Gibbs free energy and the adiabatic temperature (Tad) of three exothermic synthesis reactions were calculated. Disc-shaped and elongated TiB2 grains were synthesized in the Al2O3-TiB2 composite. Some whiskers and platelet grains were synthesized in the Al2O3-SiC composite. Nano-particles were synthesized in the Al2O3-TiC composite and distributed both within the Al2O3 matrix grains and along the grain boundaries.

Abstract: Abrasive jet machining is an efficient technology for the fabrication of three dimensional micro structures on brittle materials. In abrasive jet machining, the variation or fluctuation in the amount of abrasive supply has a significant effect on the quality of the machined structures. An image processing technique is employed in this study to study the abrasive flow rate variation, in which abrasive jet pictures are captured at different moments by a Particle Image Velocimetry technology and then processed using Labview Vision Assistant and MATLAB. It shows that the abrasive flow rate fluctuates with time under the jetting conditions considered. The abrasive flow from larger nozzles or at smaller air pressures shows more profound fluctuation. Although the abrasive flow fluctuation from smaller nozzles remains almost constant when the air pressure is changed, for larger nozzles, the magnitude of the fluctuation gradually decreases as the air pressure is increased.

Abstract: Abrasive air jet micro-machining is a new promising technology for processing brittle material. An experimental study of micro-channeling on quartz crystals using an abrasive air jet is presented. The effect of the processing parameters on the produced channel profile such as the channel width, depth and kerf taper angle is analyzed, along with the effect on the roughness of channel bottom surfaces. Plausible trends of the major process performance measures with respect to the process parameters have been revealed. These trends are useful in guiding the selection of process parameters in practice.

Abstract: Titanium alloys are difficult-to-cut materials. This paper presents an experimental study of the effects of different cutting conditions and tool wear on cutting forces in dry milling Ti6Al4V with coated carbide inserts. The experimental results show that the peak forces increase with the increase in the feed rate and depth of cut. With the cutting speed increment in the range from 50 m/min to 150 m/min the peak forces decrease, while at further higher cutting speeds investigated peak forces increase. The decrease of the peak forces is due to thermal softening of the workpiece material and the increase is because of the strain hardening rate of Ti6Al4V. The tool wear experiment reveals that the major tool wear mechanism is the flank wear. The variations of the peak forces are caused by both the tool wear propagation and the thermal effects.

Abstract: An experimental study of the machining process for micro-channels on a brittle quartz crystal material by an abrasive slurry jet (ASJ) is presented. A statistical experiment design considering the major process variables is conducted, and the machined surface morphology and channelling performance are analysed to understand the micro-machining process. It is found that a good channel top edge appearance and bottom surface quality without wavy patterns can be achieved by employing relatively small particles at shallow jet impact angles. The major channel performance measures, i.e. material removal rate (MRR) and channel depth, are then discussed with respect to the process parameters. It shows that with a proper control of the process variables, the abrasive water jet (AWJ) technology can be used for the micro-machining of brittle materials with high quality and productivity.

Abstract: A rough ground fused silica surface can be ground in a ductile mode by ultra-precision grinding after repairing the surface and subsurface micro cracks (SSMC) by CO2 laser irradiation. In this paper, 2D finite element thermal analysis of unidirectional multi-pass laser irradiation on fused silica was conducted, and the simulation results were compared with the thermal analysis and experiments results of single pass laser irradiation. Thermal analysis results show that the SSMC on the ground fused silica can be repaired and surface roughness can be decreased simultaneously by unidirectinal laser raster scan with a power of 10.5 W, a scan velocity of 0.2 m/s and a scan spacing of 40 μm.

Abstract: In micro milling, cutting parameters such as feed per tooth and cutting speed are found to have significant influence on cutting forces and surface quality. To address these issues, an experimental study of micro milling with three types of metal material (steel, brass and aluminium alloy) is conducted. The experiment setup and cutting conditions are described; the experiment results are presented with a discussion of the influence of various cutting parameters such as feed per tooth and tool diameter. These results are used to provide strategies to optimise cutting parameters and achieve better surface quality with the concern of tool diameter and material hardness when micro milling selected materials.

Abstract: Having an insight on the fluid field in AWJ machining is of important significance but the direct observation and measurement can be hardly implemented. Thus a 3D simulation of the fluid field in AWJ has been undertaken using FLUENT 6.3. The pressure and velocity distribution results on the impacted surface under different impact angle conditions are acquired and analyzed. The influence of the impact angle on the characteristics such as the symmetry of the distribution, position of the maximum value and the stagnation effect is highly concerned. In addition, an experiment under the similar conditions of the simulation is conducted and the results are compared with that of the simulation.

Abstract: Ball-end milling of Cr12MoV die steel was studied using ceramic and cemented carbide inserts under different cutting conditions. The cutting forces, wear patterns and chip patterns generated using the different cutting tools at the different cutting conditions were investigated using a three component piezoelectric dynamometer and VHX-600E large depth-of-view 3-D scanner. The relationships among the cutting forces, wear patterns and chip patterns were discussed. The results indicated that the cutting forces caused by the ceramic insert were slightly lower than those caused by the cemented carbide insert under the same cutting conditions. For ceramic inserts, effects of cutting conditions on the rake face wear were different from those on the flank wear. The higher wear for the ceramic insert was caused at the lower cutting conditions but the higher wear for the cemented carbide insert was encountered at the higher cutting conditions. The squeezed chip was involved with the higher cutting forces. The sharper cutting edge of the cemented carbide insert was responsible for chip patterns caused by the No. I cutting condition. The effects of cutting conditions on wear patterns were more evident than that on chip patterns.