Effect of Periodic Drilling Force on Instability in a Drilling Process

Abstract

The periodic drilling force effect on the dynamic instability of a drill in a drilling process was investigated. This investigation involves the cutting geometry drilling force from the two active parts of a twist drill subjected to small fluctuations during the drilling process. Theoretically, at some drilling force, this small drilling force fluctuation may lead the system into a dynamically unstable condition. Most hole location errors, reaming, and drill fractures occur in this unstable drilling process phase. The dynamic instability in a drilling process is an important issue in increasing the drilling quality and production rate. In this article, a pretwisted beam with a moving Winkler-type elastic foundation is used to simulate the drill and drilling process. Numerical analysis indicates that the unstable regions are enlarged and shifted to a lower frequency suddenly as the drill bites into a workpiece. It is also observed that the thrust force, spinning speed, and pretwisted angle effects drastically change the dynamic instability of drilling.