Modelling and evaluation of the micro abrasive blasting process

Abstract

Micro abrasive blasting (MAB) is becoming an important machining technique for the cost effective fabrication of micro devices. The material removal process is based on the erosion of a mask-protected brittle substrate by an abrasive-laden air jet. To exploit the potentials of this technique for applications of industrial interest, the blasting process has to become more efficient and better predictable. Therefore, in this paper micro-abrasive blasting is analysed by means of a set of models containing different sub-models for the particle jet, the erosion mechanisms of a single particle impact and the machining results. A one-dimensional isentropic flow model was developed to calculate the particle exit velocity of each individual particle in the airflow for two different types of nozzles: a converging cylindrical and a new developed line shaped Laval-type. The particle size and its position within the air jet are based on probability distribution functions. The result is a nozzles characteristic energy intensity distribution of the particle beam. Subsequently, classical indentation fracture mechanics is used to model the interaction between incoming particles and the substrate surface. The simulation shows that the Laval-type nozzle is able to increase the particle velocity with more than 30% compared to the converging nozzle. Also the blasting profile is more uniform with a relatively flat bottom. Experimental verifications of the particle velocities using particle image velocimetry (PIV) and measurements of the roughness and the shape of the blasting profile demonstrate that the presented model is capable to predict accurately the blasting performance of both nozzles types.