Abstract
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 of the mask opening size and powder shape and size 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 allow for their use in surface evolution models that can predict the evolving shape of features micro-machined using AJM.
Highlights
The jet of high speed impacting particles is usually passed through very narrow openings in a patterned erosion-resistant micro-mask which protects the substrate against particle impacts, defining the features to be machined (Fig. 1.1)
Since the shadowgraphy technique is independent of the shape and material, it can be used to measure the particle size and velocity distribution in the abrasive jets used in abrasive jet micromachining (AJM) technology
Limitations on applicability of results: The results of the present study directly show that, if the particle size distribution is measured, under the present blasting conditions, the model of Ghobeity et al [6] can be used with confidence in surface evolution models in order to predict the size and shape of features machined using AJM
Summary
Particle velocity Maximum velocity of the incoming particle Velocity at the periphery of the jet Incoming particle velocity at any radial position of the jet Particle velocity at (x, y) position from the nozzle tip Particle velocity at the nozzle center line Particle velocity at the end point of the ith segment of the nozzle Centre line velocity of air flow at an axial distance x from nozzle exit Particle velocity at the start point of the ith segment of the nozzle Mask opening width Distance from nozzle exit in jet flow direction Divergence angle of the nozzle Expansion angle of abrasive air jet flow Angle of exit with respect to the nozzle centerline Air density at nozzle cross section Density of abrasive particle Air viscosity at room temperature Experimentally determined jet focus coefficient Particle sphericity Angle with a uniform random number on the interval [m/s] [m/s] [m/s] [m/s] [m/s] [m/s] [m/s] [m/s] [m/s] [μm] [mm] [Degrees], [Radians] [Degrees], [Radians] [Degrees], [Radians] [kg.m−3] [kg.m−3] [kg.m−1s−1] [non-dimensional] [non-dimensional] [Radians]
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