Receptance Coupling For Tool Point Dynamics Prediction On High Speed Machine And The Milling Stability Analysis

High-speed milling with advantages of high efficiency, low cost and good accuracy inthe large, complex parts processing, has been widely used in aerospace, the automotiveindustry, shipbuilding industry and mold parts processing industry. Chatter is the mainfactor that affects the machining quality and efficiency. One of the ways to avoid chatter isto predict the stability lobe diagram (SLD) which is based on the tool endpoint frequencyresponse function, and select stable milling conditions. In previous studies, the toolendpoint frequency response function was measured through hammer test or the finiteelement method. Due to the wide variety of tools and holders, one need to repeat the modaltests for each assemble of tool and holder, which is time-consuming and laborious. Inaddition, due to the effects of gyroscopic and centrifugal force, the stiffness of electricspindle and the angular contact ball bearings decrease with the increase of spindle speed.The dynamics of the system is completely different from the stationary state, and the effectsof the variable stiffness on the dynamical characteristics must be taken into account.In this thesis, the model of the spindle-holder-tool system supported by the elastomericbearing is firstly build with the receptance coupling system analysis (RCSA) method andTimoshenko beam theory. The milling system is divided into three parts, spindle, holder,and tool with flexible connections (springs and dampers), which can be obtained through ahammer test. For a given tool or holder replacement, with no additional modal test needed,one can obtain the frequency response function through creating the new tool or holderbeam model, and coupling them to the known spindle dynamics. In this procedure, one alsocan consider the bearing characteristics and gyroscopic effect on the dynamiccharacteristics of the system. To verify the approach, a test rig for the spindle150ES15-20Lwith holder-tool system is set up and the modal test is carried out.In order to study the effect of system dynamics and higher modes on the stability ofmilling processes, a multi-degree-of-freedom model of the flexible workpiece-tool systemis established in two orthogonal directions. Due to the intermittent of milling process, thecutting force can be expressed as discontinuous functions of chip thickness, and theequations are differential delay equations with periodic coefficients. These equations areboth solved in the frequency domain and in the time domain, with the semi-discrete methodand numerical integration, respectively. In the frequency domain, the Floquet theory is usedto determine the stability of the solution and the effects of variable bearing stiffness andspeed-depend dynamics on milling stability are discussed. In the time domain, the Poincaremap is used and the bifurcation diagrams and milling stability are further analyzed.