MECHANICAL EFFECTS OF ULTRASOUND CLEANING ON NITINOL MICRO-COMPONENTS--INVESTIGATING VIBRATION DYNAMICS DURING ACOUSTICAL CLEANING PROCESSES

摘要

Ultrasonic cleaning is the gold-standard method to clean micro components like stents from a wide range of particle types and sizes. Material interactions during cleaning arise from ultrasonic induced excitations and imploding cavitation bubbles, however, the mechanical impact on the material and geometrical structure is still unclear. Crush-force measurements are used to evaluate the mechanical impact of ultrasound. Discontinuities (cracks/voids and tight radii as occurring in tip-areas) on the stent surface are identified as preferred sites of bubble formation. Real-time laser vibrometry and advanced image-processing techniques are applied to investigate vibration dynamics during ultrasound exposure with typical process parameters. Effects of ultrasound on crush-force remain inconclusive since force measurement is highly dependent on stent position. Ultrasound appears to have no significant negative impact on surface quality of Nitinol stents. Even cracks present before ultrasonic excitation do not show any further propagation after ultrasound exposure. There is no indication of ultrasound being a cause of micro cracks or voids. Marker material (Gold) shows severe erosion when being exposed to ultrasound. Stents are excited by frequencies occurring in ultrasonic cleaning baths with a corresponding displacement in the range of +-50nm.