Low-Frequency Regenerative Vibration and the Formation of Lobed Holes in Drilling

Abstract

Large-amplitude vibrations in drilling often occur at frequencies near multiples of the rotation frequency, even when these are much lower than the system’s first natural frequency. These vibrations are responsible for out-of-round, “lobed” holes. A simplified model of the mechanics of this phenomenon is presented in this paper. The model includes cutting and “rubbing” forces on the drill, but inertia and damping of the tool are neglected at low speeds. This quasi-static model remains dynamic because of the regenerative nature of cutting; the force on each cutting element depends on both the tool’s current position and its position at the time of the previous tooth passage. Characteristic solutions, including unstable retrograde “whirling” modes, are found in terms of eigenvalues and eigenvectors of a discrete state-transition matrix. These unstable modes correspond closely to behavior observed in drilling tests.

Generalized modeling of drilling vibrations. Part II: Chatter stability in frequency domain

“…The torque acting on the drill unwinds the drill, while the bit elongates at the same time, which leads to a chip thickness regeneration mechanism in axial direction. Bayly et al also developed models to predict the hole shape resulting from reaming operations [19,20] and drilling [21]. Dilley [22] focused on lateral chatter in drilling.…”

Noise-Sensitivity in Machine Tool Vibrations

“…In all examples the goal is to understand the source of chatter in order to avoid it. Certain models have considered the effect of variable speed on chatter [20,21], as well as understanding the nonlinear behavior with a frequency different from the natural frequency of the system [19] [22]. Other issues include the geometry of the cutting which can affect the bifurcation structure of the nonlinear behavior [23].…”

“…The dynamics of machine tool vibrations have been studied from a variety of perspectives, including analysis, computations, and experiments (see [12]- [19] and references therein). In all examples the goal is to understand the source of chatter in order to avoid it.…”

Burr height and hole diameter error minimization in drilling of AL6063/15%/SiC composites using HSS step drills

“…They revealed that high frequency vibration is the most common cause for roundness problem in drilled holes. Authors also explained that low frequency vibration is significant for drilling because it directly affects hole quality [17]. The study investigated the influence of the factors on thrust force, diameter, and roundness deviations while drilling glass fiber reinforced epoxy resin with high speed steel and cemented carbide drills.…”