Session: 07-01-05: General Dynamics, Vibration, and Control

Paper Number: 114620

114620 - A Unified Process Damping Model in Cutting With Velocity and Ploughing Effects 

Chatter is a self-excited vibration in machining, which may cause tool damage and low quality of surface. The most common methods to avoid the chatter are optimization of cutting parameters based on the predicted stability lobe diagram (SLD) which plots the ultimate stable depth of cutting at different spindle speeds. Therefore, it is important to accurately predict the SLD. The classical regenerative chatter theories using delay-differential equation can provide accurate SLD at relatively high speeds. However, the experimental results show that the actual SLD shifts toward a higher stable depth of cutting at low speeds, resulting in a larger stable region. Most researches attribute the stability improvement at low speeds to additional dissipative force during cutting. The additional term is called process damping force. Since process damping plays a significant role in the improvement of the machining stability, modeling of the process damping is a crucial premise for accurate prediction of the SLD, especially at low spindle speeds.

The process damping is mainly explained by two factors, i.e. the velocity-dependent effect and the ploughing-indentation effect. The velocity-dependent effect originates from the difference between the actual cutting velocity and nominal one during machine tool vibration, which modifies the magnitude and direction of dynamic cutting force. The ploughing-indentation effect is generated by the extrusion between the flank face of the tool and the wavy machined surface of the material, which increase the indentation force and friction force. In most existing papers, only one factor are considered to establish process damping model for simplified calculation.

This study aims to build a unified process damping model in cutting considering both velocity-dependent and ploughing-indentation effects, and to analyze the effect proportion of the two factors in different machining conditions. In the modeling, the two conversion coefficients K_v-d and K_p-I are attributed to the velocity-dependent effect and ploughing-indentation effect, respectively. The two coefficients quantify the influences the two factors on process damping, which is used to unveil the variation between the effect proportion of two factors and the machining parameters. Since the nonlinear delay-differential equation with velocity-dependent and ploughing-indentation effects will increase computation difficulty, the additional indentation force and friction force are converted to equivalent viscous dampings for calculation simplification. The delay-differential equation with velocity-dependent and ploughing-indentation effects is solved by the numerical integration method to predict the SLD. Experimental results demonstrate the proposed unified model considering two effects has better predictive accuracy compared with the existing models. The study can better guide machining operators to select optimal machining parameters for machining efficiency improvement.

Presenting Author: Yan Ru Jiang Huazhong University of Science and Technology

Presenting Author Biography: Jiang Yan ru is now a phd student, supervised by assciate professor zhang xiaojian, her major is machining dynamics .

Authors:

Yan Ru Jiang Huazhong University of Science and Technology
Xiaojian Zhang Huazhong University of Science and Technology