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Part I of this two-part paper presented mixing chamber conditions and jet characteristics in a high-pressure abrasive slurry jet micro-machining (HASJM) system. The present paper describes the modeling of the slurry entrainment process within the mixing chamber and mixing tube of the nozzle using computational fluid dynamics (CFD) and shows how the results can be used to explain and predict machining performance. The slurry flow rate into the mixing chamber was found to have a large impact on the performance of the jet due to differences in the momentum of the high-velocity water and low-velocity slurry. The erosive efficacy of the jet was assessed by machining channels and blind holes in aluminum 6061-T6. Differences in the centerline erosion rates of holes and channels for a given jet showed clear evidence of incubation and stagnation zone effects. The CFD models simulated various slurry flow rates entering the mixing chamber as a result of the low pressure created by the central high-velocity jet of water. They predicted correctly an experimentally observed flooding condition in which slurry completely filled the mixing chamber and mixing tube. The models could also identify the transient conditions leading to the onset of this flooding as the chamber first began to fill, which could not be identified experimentally. Flooding was found to significantly reduce the jet velocity, thus diminishing its erosive efficacy. The models also identified the operating conditions within the mixing chamber that produced boiling due to the low internal pressure generated by the central high-velocity jet of water. This boiling condition was found in part I to result in a wider jet exiting the mixing tube. [ABSTRACT FROM AUTHOR]

Techniques to enhance the performance of a high-pressure abrasive slurry jet micro-machining process (HASJM) were investigated by altering the conditions within the jet. The slurry flow rate was controlled using six inlet tubes (cross-sectional areas of 0.2, 0.46, 1.27, 1.77, 3.08, and 4.51 mm2), and was found to have a large effect on the conditions within the mixing chamber. The tubes permitted the use of high-concentration slurry solutions, which resulted in increased machining rates and the ability to machine glass targets without cracking by using a minimum particle concentration of 17 wt%. Slurry tubes producing large slurry flow rates caused the mixing chamber to flood, resulting in a much lower jet velocity. The size of the smallest slurry tube size that caused the mixing chamber to flood was dependent on the pump operating pressure, and varying from 1.27 mm2 at 134 MPa, to 1.5 mm2 at 233 MPa. Mixing chamber flooding significantly reduced the erosion rate of the jet and increased the machining time, as discussed in the second part of this two-part paper. Mixing chamber pressures were found to be low enough to cause boiling, which increased the jet diameter and the width of features that could be machined without a mask. [ABSTRACT FROM AUTHOR]

Vibratory finishing (VF) employs vibrationally-fluidized granular media to finish the surfaces of workpieces that are entrained in the flowing media. Its application has been based mostly on experience and trial-and-error due to the complexity of the granular material behavior. The present study used discrete element modeling (DEM) to investigate how the movement of a commercial two-dimensional tub finisher influenced the average particle speed of the media in a bed of smooth, steel, spherical particles, and thus the work that would be done on an entrained workpiece. The parameters governing the tub wall motion (frequency, in-plane amplitudes, and phases of vibration) and the coefficient of friction between the media and the wall were systematically varied in 71 three-dimensional DEM simulations. The average particle speed was affected mostly by the vertical amplitude of tub motion rather than by the frequency, and was mostly independent of other parameters of motion and of the wall friction. A strong relationship was found between the average particle speed and the work done by the wall per cycle of vibration. The normal force on the wall was also found to correlate strongly with the normal component of the wall velocity. Together, these relationships offer the potential to enable the analytical prediction of the average particle speed based on the motion parameters of the tub alone. The paper provides a set of practical guidelines for the control of the average particle speed in VF that are explained by the forces between the media and walls of the tub finisher. [ABSTRACT FROM AUTHOR]