Predictive modeling of the micro-hole profile drilled by a high-power electron beam

Abstract

Hole drilling is one of the most important and necessary manufacturing processes. From mechanical connection with bolts and pins to production of micro filters at automotive and aircraft, the drilled hole has a wide variety of applications. Especially, in manufacturing such parts, micro-hole drilling is required as an optimization method that maximizes surface area of product or minimizes stresses in mechanical assembly or fluidic system. Electron beam drilling can generate hole with diameter of submicron scale, while maintaining high-aspect ratio (high ratio of hole depth to diameter). Even though studies related to hole drilling with mechanical type or energy-beam type been constantly carried out, researches about drilling with electron beam have been limited. In addition, among the electron beam researches, analysis using numerical predictive model tended to be focused in the field of electron beam welding. Accordingly, in this dissertation, numerical prediction was attempted for micro-hole drilling of high-power electron beam withacceleration voltage of 120 keV. Based on the principle of heat dissipation, numerical predictive model that can be interpreted by finite difference method (FDM) was constructed. Predictions of temperature distribution were conducted, reflecting Gaussian beam profileand thermal properties on meshed substrate. And the energy absorptance mechanism by accelerated electrons were applied in this model. The hole profiles resulted from electron beam penetrating were evaluated by two criteria: ideal minimum area which is part over vaporization temperature and ideal maximum area which means part over melting temperature, on results of the meshed substrate. When the beam reaches interface between substrate and backing material, removal between ideal minimum area and maximum area of hole profile was performed in order to implement the principle of backing material explosion. To verify the precision of the model, practical experiments was processed using micro-hole drilling system that can generated high-power electron beam. While the acceleration voltage was maintained at 120 kV, changing beam current, beam power was varied from 720W to 1440W. Drilled holes on AISI 304 stainless steel were classified by beam power. The hole profiles were analyzed without physical deformation, by using micro CT. Through binary processing and pixel calibrating of CT image, the average of hole profiles was obtained in a statistical method. The precision ofthe simulation model was verified by comparing experimental and analytical results, and the analysis and discussion for physical meaning were performed.