Improvement of process repeatability and resolution in abrasive air jet machining via viscous slurry entrainment

Abstract

The unsteady powder mass flowrate of the available feeding systems and the bad control of the areas being eroded have been often noticed in the abrasive air jet machining process. In addition to the delivery of dry powder, the powder can be evenly mixed with liquid to form a slurry, and then sent to the mixing chamber of an air jet machine; i.e., multiphase jet machining (MJM) was proposed in this paper. The method whereby using the viscous water to suspend the abrasives was found to enhance the stability of powder mass flowrate, thereby decreasing the fluctuation in the machining depth. Whereafter, five types of liquid-based slurries were prepared and their effects on the jet erosion zone were investigated. It was found that the control of the erosion zone was improved to varying degrees when the abrasives were transported into the air jet by viscous liquid as the carrier fluid due to the two roles: reducing the occurrence of third and/or second particle impacts; inducing a viscous boundary layer that could reduce the negative effect of the divergence of jet beam and particle rebounding. In particular, the use of an oil-based slurry could completely eliminate the unwanted frosted zone around the machined features. CFD simulations were used to understand the mechanisms causing these effects. Overall, it is shown that the abrasive air jets can be designed to have a good resolution, so it is feasible to mill or polish surface without the need for a mask to define the edges.