Investigation of Step Micro-Drilling Motion Based on Modeling of High Speed Spindle Driving Axis on Machine Tools Equipped with Vibration-Proof Mechanism

Abstract

Recently, there has been an increasing demand for miniaturization and multi-functionalization of electronic equipments due to the developments in information technology (IT). Thus, the miniaturization of printed wiring boards (PWBs) and fabrication of highly dense electrical circuit layers are needed to realize the miniaturization and densification of the semiconductor package PWBs. Micro-drilling technology has been attracing attention to machine the electronic micro-through holes with an ultra-high-speed spindle, more than 160 krpm. However, problems have emerged; the drill tool bends and suffers breakage in the drilling process and the heat damage around the drilled hole after a drilling process occurs due to the increase in the drilling aspect ratio between hole depth and diameter. In general, a step feed drilling method is considered an effective way to solve these problems. However, short stroke alternating motion in the spindle axis is needed to do the step drilling process and its motion causes various kinds of vibration. We constructed a machine tool with a novel counter balance mechanism in the spindle driving Z-axis and investigated a model to estimate a proper balance mass for the step drilling process. We compared the frequency response results from a proposed model with the experimental ones, and discussed a control on vibration due to the counter balance mechanism. The results demonstrate that a proposed vibration proof method was found to reduce the vibration in high-speed step-micro-drilling motion and to improve the drilled hole quality and the efficiency of micro-drilling process in the PWB manufacturing fields.