Acoustic chamber length performance analysis in ultrasonic pulsating water jet erosion of ductile material

Abstract

Ultrasonic pulsating water jets are a technological modification of water jet technologies that disintegrate materials at pressures <= 100 MPa. Disintegration occurs at a non-systematically determined standoff distance z [mm] as a result of variable axial jet speeds determined by the acoustic chamber length. Water velocity fluctuations are converted from pressure fluctuations present in the acoustic chamber using a nozzle. Pressure fluctuations are generated by an ultrasonic sonotrode with a frequency of 20 kHz. The impulse travels through the acoustic chamber, which is geometrically designed to vary its length from 0 mm to 25 mm with a mechanical nut. A PWJ system can be tuned within this interval to achieve the desired PWJ performance. Until now, the synergic effects of the standoff distance z [mm] and the acoustic chamber length l(c) [mm] on material interactions have not been clarified in the literature. Therefore, this study discusses how the length of the acoustic chamber lc is related to the nozzle's standoff distance z [mm] from the surface of the material and from the point of achieved maximal depth h [mm]. The length of the chamber was gradually increased by one millimetre from 5 to 22 mm. Subsequently, PWJs with p = 30 MPa and 40 MPa were tested. The robot arm carrying the nozzle head travelled along a programmed trajectory at an angle of 16 degrees starting from z = 5 mm with a traverse speed v = 5 mm/s. It has been found that the effect of acoustic chamber length on the disintegration within an erosion interval has a hyperbolic course.