Laser shadowgraphy measurements of abrasive particle spatial, size and velocity distributions through micro-masks used in abrasive jet micro-machining

Erosion modeling in abrasive slurry jet micro-machining of brittle materials

“…An automated image analysis system (Clemex Vision PE, Clemex Technologies Inc., QC, Canada) was used to measure the actual size distribution of the particles, which was found to vary between 8 and 53 m with a mean diameter of 22 m [13]. This was in good agreement with the size distribution measured by Dehnadfar et al [14] using laser shadowgraphy. The uniformity and repeatability of the slurry concentration was measured by collecting 10 samples of 50 mL each from the orifice.…”

“…The measurement of the particle velocity at the instant of impact is difficult in a slurry jet. High resolution imaging with laser-pulsed backlight illumination (shadowgraphy) has been used to measure particle velocities in air jets, which can then be assumed approximately equal to the impact velocities [14]. However, as mentioned above, the high fluid viscosity of a slurry jet means that the impact velocity will be quite different from the particle velocity in the free jet.…”

“…Particle-particle interactions were considered negligible, as were the effects of particles on the flow field. Drag calculations approximated the non-spherical shape of particles by using an average shape factor of 0.76 (ratio of surface area of a sphere having the particle volume to the actual particle surface area), as measured by Dehnadfar et al for the 25 m alumina powder [14]. The rebound of abrasive particles after their initial impact was modeled using a coefficient of restitution of 0.3, which was selected based on the 0.2-0.5 range found by Slikkerveer and in't Veld [22] for alumina particles impacting borosilicate glass [23].…”

Calibrated CFD erosion modeling of abrasive slurry jet micro-machining of channels in ductile materials

“…These forces include the drag force, the pressure gradient force and the added mass force, as suggested by Zhang et al [29]. The particle shape factor (ratio of surface area of a sphere having the particle volume to the actual particle surface area) was set at 0.76 for the 10 m nominal diameter angular Al 2 O 3 abrasives, as measured by Dehnadfar et al [30]. For erosion modeling, the discrete random walk (DRW) model was used to account for any possible changes in the particle trajectories caused by flow turbulence.…”

Abrasive Jet Micro-Machining of Polymeric Materials

“…The average mass flow rates of the 136 µm and 103 µm nominal diameter garnet particles were 2.74 g/min (3 measurements, standard deviation 0.04 g/min) and 3.41 g/min (3 measurements, standard deviation 0.17 g/min). The distributions of the particle velocity, and the particle size and shape (area and aspect ratio) were measured (Section 3.4) within the jets using a laser shadowgraphy system (LaVision GmbH, Goettingen, Germany) described in detail in [119]. The shadowgraphy measured average aspect ratio (0.66) was in good agreement (12% difference) with the average aspect ratio measured using the optical microscope (0.75).…”