Influence of the Impact Angle on Machining in Powder Jet Processing

Powder jet machining is a blast machining process in which micrometer-order particles are projected onto a workpiece at near-supersonic speeds, to remove the workpiece (abrasive jet machining (AJM)) or to deposit the particles (powder jet deposition (PJD)). We report a novel dental treatment method for powder jet machining using hydroxyapatite, which is the main component of teeth, as deposited particles. The surfaces and interdental spaces of human teeth are not only flat, but also have complex groove struc-tures. However, PJD and AJM exhibit impact-angle-dependent machining phases. Therefore, it is neces-sary to investigate the effect of the particle impact angle on machining, before dental treatment. Further-more, because machining interacts not only with the particle impact angle but also with the particle impact velocity, a comprehensive investigation of the effects of the machining parameters is required, for delineat-ing the phase-transition conditions. Accordingly, in this study, we conducted machining experiments using hydroxyapatite particles (particle diameter, 2.16 μm) and four different blasting angles of 30°, 45°, 60°, and 90°, to infer the machining amount. Machining efficiency was evaluated based on the amount of ma-chining. The impact angles and velocities of the particles were calculated using computational fluid dynamics (CFD). Three-dimensional process mapping was performed using the machining amount, particle impact angle, and particle impact velocity, obtained from the experiments and CFD calculations. The results showed that PJD crossed to AJM at the impact angle of approximately 60°. Moreover, PJD exhibited high processing efficiency for impact angles above 60° and impact velocities in the 280–310 m/s range. In con-trast, AJM exhibited high processing efficiency for impact angles below approximately 35° and impact velocities above 310 m/s.