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1.
In abrasive jet micromachining (AJM), a jet of particles is passed through narrow mask openings in order to define the features to be micro-machined. The size and shape of the micro-machined features depends on the distribution of the particle velocity and mass flux through the mask openings. In this work, a high speed laser shadowgraphy technique was used to demonstrate experimentally, for the first time, the significant effect that the mask opening size and powder shape and size have on the resulting distribution of particle mass flux and velocity through the mask opening. In particular, it was found that the velocity through the mask was approximately constant, but different in magnitude than the velocity in the free jet incident to the mask. The measured mass flux distributions were in excellent agreement with a previously developed analytical model, thus directly confirming its validity. Additional measurements also showed that an existing numerical model could be used to predict the velocity distribution in free jets of spherical particles, and, if a modification to the particle drag coefficient is made, in free jets of angular particles. The direct experimental verification of these models allows for their use in surface evolution models that can predict the evolving shape of features micro-machined using AJM.  相似文献   

2.
A novel implementation of narrow band level set methods (LSM) was used to predict the surface evolution of inclined masked micro-channels in glass and poly-methyl-methacrylate (PMMA) made using abrasive jet micro-machining (AJM) at oblique incidence. The resulting inclined PMMA channels had straight walls and rectangular bottoms, while the glass profiles had curved walls and rounded bottoms. The inclined micro-channels rapidly become multi-valued, and the Hamilton–Jacobi type partial differential equation describing their evolution cannot be solved using traditional analytical or numerical techniques. To predict the decrease in particle flux at the mask edge, a previously developed analytical model was generalized from the normal to the oblique incidence case. The local surface velocity function was non-convex, necessitating the development of a modified extension velocity methodology to address the problem of grid ‘visibility’ of the particle flux. The agreement between LSM-predicted and measured surface evolution was fair. Since in its current form the model ignores particle ‘second-strike effects’ and mask wear, it is best suited to predict AJM surface evolution in ductile targets where mask wear is minimal, and not for brittle targets (e.g. glass). Since AJM at oblique incidence can be used to machine three-dimensional suspended micro-structures, the work has important implications for the micro-fabrication of novel MEMS and microfluidic devices.  相似文献   

3.
A previous implementation of narrow band level set methodology for the modelling of the surface evolution of masked features in abrasive jet micro-machining (AJM) including the effect of mask erosive wear was extended to include the effect of particle second strikes. The model uses a ray tracing/node tracking algorithm to allow the prediction of the effect of particle ricochets from the mask edges and the sidewalls of the machined feature on the resulting surface evolution of high aspect ratio features. Using the model, for the first time, the prediction of the particle second strike effects from inclined masked features is made possible. When compared to previous models that did not account for mask wear and second strike effects, the present model significantly improved the prediction of measured masked micro-channels machined using AJM in glass. When compared to previous particle tracking computer simulations, the present model was found to have a much shorter execution time, and in some cases also showed an improved prediction. The model can be useful in predicting the feature shape in the AJM of brittle targets for aspect ratios greater than 1, and hence for the micro-fabrication of microfluidic and MEMS devices.  相似文献   

4.
A novel and generally applicable computer simulation was developed to predict the time evolution of the eroded profiles of air abrasive jet machined surfaces, as a function of process parameters such as: abrasive nozzle size, inclination and distance to target surface, abrasive jet particle velocity, size and flux distribution. The effect of collisions between incoming and rebounding particles was included by the tracking of individual particles, performing inter-particle and particle to surface collision detection, and implementing collision kinematics. The target surface advancement was determined by representing the surface by a grid of cubic cells, each of which was assigned a damage parameter based on the number of particles impacting it. The predictions of eroded profiles of the simulation were tested against those that are experimentally measured for a typical microabrasive blasting setup, with good agreement at low particle flux, and reasonable agreement at high particle flux.  相似文献   

5.
A phenomenological model of the three-phase flow inside an abrasive water jet machining cutting head has been developed. Several improvements over previously presented models such as taking into account the abrasive particle size distribution, and the effect of breakage of particles on the energy flux have been made. The model has been validated using an extensive set of experimental data with wide variations in cutting-head geometry, operating pressure, and abrasive mass flow rates. The cross-sectional averaged abrasive particle velocity at the exit of the focussing tube has been predicted with good accuracy over the whole range of experiments. In particular, the Pearson correlation between the model and the experimental results is found to be more than 95%, implying the utility of this model in design.  相似文献   

6.
Abstract

Erosive abrasive wear is caused by high speed impact of particles entrained in a fluid system on the surfaces of components such as boilers and furnaces. Erosive abrasive wear in boilers results from the impact of hard particles such as ash or clinker entrained in flue gases and can lead to serious damage. The life of boiler and furnace components encountering erosive abrasive wear in service, which are most commonly fabricated from carbon steels, can be improved by hardfacing with a wear resistant material. The effects of wear parameters such as particle size, flux and velocity on the erosive abrasive wear behaviour of a stainless steel surface produced by the plasma transferred arc hardfacing have been investigated using an experimental design approach. The wear resistance of the stainless steel surface was found to be twice that of the carbon steel substrate.  相似文献   

7.
An aluminum base composite (Al-SiC) powder has been developed for producing plasma sprayed coatings on Al and other metallic substrates. The composite powders were prepared by mechanical alloying of 6061 Al alloy with SiC particles. The concentration of SiC was varied between 20 and 75 vol%, and the size of the reinforcement was varied from 8 to 37 μm in the Al-50 vol% SiC composites. The 44 to 140 μm composite powders were sprayed using an axial feed plasma torch. Adhesion strength of the coatings to their substrates were found to decrease with increasing SiC content and with decreasing SiC particle sizes. The increase in the SiC content and decrease in particle size improved the erosive wear resistance of the coatings. The abrasive wear resistance was found to improve with the increase in SiC particle size and with the SiC content in the composite coatings.  相似文献   

8.
Nano-scale scratching in chemical-mechanical polishing   总被引:2,自引:0,他引:2  
N. Saka 《CIRP Annals》2008,57(1):341-344
During chemical-mechanical polishing (CMP) in the fabrication of advanced semiconductor devices, undesirable nano-scale scratches are produced, especially in the presence of low-k dielectrics. In this paper, the lower- and upper-bound loads for scratching are estimated by contact mechanics models and are validated by AFM experiments. Additionally, the width and depth of scratches are related to such process parameters as: particle size, abrasive volume fraction, mechanical and geometric properties of the pad and surface coatings, and polishing pressure. The upper-limit for scratch width is found to be a function of the particle size and the hardnesses of the coatings and the pad. In Cu CMP this limit is about one-fifth of the abrasive diameter.  相似文献   

9.
The thermal conductivity of diamond/copper composites with bimodal particle sizes was studied.The composites were prepared through pressure infiltration of liquid copper into diamond preforms with a mixture of 40 and 100 μm-size diamonds.The permeability of the preforms with different coarse-to-fine volume ratios of diamonds was investigated.The thermal conductivity of the diamond/copper composites with bimodal size distribution was compared to the theoretical value derived from an analytical model developed by Chu.It is predicted that the diamond/copper composites could reach a higher thermal conductivity and their surface roughness could be improved by applying bimodal diamond particle sizes.  相似文献   

10.
Two-body abrasive wear is a process with strong stochastic characteristic. Abrasive particle geometry, distribution and worn surface morphology can only be statistically determined and analytical models therefore always cause large inaccuracy. In this research, the earlier model of a particle as pyramid with a hemispherical tip has been replaced by a paraboloid model of revolution. In the pyramid model the normal load cannot be large enough to penetrate beyond the height of the hemisphere. Generally, in practice the hemisphere tip is quite small, and it readily penetrates into the surface. A new particle model has, therefore, been devised to extend the normal load range. New contact equations are proposed for the particle geometry used in the present model. The Monte Carlo method and finite element methods (FEMs) have also been combined to calculate the wear rate of the material during simulation. It is found that the linear wear rate increases continuously during the running-in process and reaches a constant value after some travel distance. Computed roughness and worn surface morphologies are in agreement with the experimental data. Finally, a comparison between simulated and experimented wear rates has also made. Both data matched very well.  相似文献   

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