Influences of impact loading rate on the protective effect of shims on breakage of inserts in intermittent cutting

In high-speed cutting, the shim-insert system is subjected to high-speed impact loads, and different stiffness of the shim-insert system exhibit varying impact responses at different load rates, which in turn affect the wear and damage of the inserts. This paper investigates the effect of load impact rate on the protective performance of weak stiffness shims. A mass-spring vibration model for the shim-insert system is established to analyze the effect of load rate on the inertial forces within the system. Finite element analysis is conducted to explore the influence of impact load rate on the stress distribution at the tool tip for four different shim stiffness levels. Additionally, intermittent cutting experiments using four different stiffness shims are performed to study the impact of load rate on cutting forces, vibration acceleration, and insert fracture under different cutting speeds (load rates). The results show that as the impact load rate increases, the protective effect of weak stiffness shims on the inserts gradually weakens. At low impact load rates, the shim reaction force dominates, and the inertial force of the insert can be neglected. As the load rate increases, the inertial force of the insert increases and becomes dominant, while the shim reaction force gradually diminishes. As the cutting speed increases (from 500 r/min to 900 r/min), the weak stiffness shim's ability to reduce cutting force weakens (from 13.44 % to 4.17 %), the inhibition of vibration acceleration amplitude decreases (from 40.47 % to 9.57 %), and the reduction in rake face damage diminishes (from 75 % to 11 %). Therefore, under high-speed impact, the protective effect of weak stiffness shims weakens, leading to a reduction in tool protection performance.