Boring bar with constrained layer damper for improving process stability

Boring is one of the most common operations to enlarge or finish predrilled deep holes and is usually conducted in low spindle speed ranges. Due to low dynamic performances of conventional boring bar, boring operation is often hindered by drastic vibration. In this paper, a design and optimization method of a special boring cutter with constrained layer damping (CLD) bar is developed based on the CLD beam theory and finite element method (FEM). The boring cutter designed is composed of four modules: cutting head, substrate layer, damping layer, and constrained layer, which can greatly improve the dynamic performances in boring process. Meanwhile, the effectiveness and capability of boring cutter with CLD bar for forced- and chatter-vibration suppression are presented based on experimental and numerical methods. The results show that (1) the method for restraining forced vibration is different from that for chatter suppression. The former can be greatly avoided by shifting the natural frequency of boring system, e.g., changing dynamic stiffness. The latter, due to its complexity in low spindle speed range, on the other hand, cannot be entirely avoided and can only be eliminated by reducing the possibility of occurrence, e.g., increasing damping. (2) The boring cutter with CLD bar developed can change dynamic stiffness through constrained layer and improve damping performance through damping layer. So, it can avoid forced vibration and eliminate chatter to some extent. In the presented parameter domains, the capability of CLD bar for chatter suppression is improved five times corresponding to that of conventional bar.