Modelling part dynamicsin machining processes considering material removal


Thesis Type: Postgraduate

Institution Of The Thesis: Middle East Technical University, Faculty of Engineering, Department of Mechanical Engineering, Turkey

Approval Date: 2007

Thesis Language: English

Student: Sibel Atlar

Supervisor: HASAN NEVZAT ÖZGÜVEN

Abstract:

Self-excited chatter vibration in machining is one of the most important limitations on utilizing the increasing productivity of modern machine tools. In order to predict stable depth of cuts at high cutting speeds, the stability lobe diagram for a spindle-tool holder-tool combination must be developed. The frequency response function (FRF) of the system must be known for analytical prediction of the stability lobe diagrams. When the flexibility of the workpiece is important, the workpiece itself should be included in the system model by considering the variation of its dynamics at different stages of the machining process. In this thesis, an exact structural modification method is used to find the frequency response functions of the workpiece to be machined at every stage of the machining process. In order to obtain the system matrices and the modal parameters of the original structure, a commercial finite element program MSC. Marc© is used. The frequency response functions of workpiece are calculated by using the computer program developed in this thesis, and are compared with the ones found by MSC. Marc©. The stability lobe diagram of the system is obtained by combining the FRFs of the tool with those of the workpiece. The effects of the dynamic of the workpiece on the stability lobe diagrams are studied extensively by using the results of case studies presented in this thesis. In order to increase productivity, minimum chatter-free machining times are also calculated for different cases. For this purpose the effects of the different radial depth of cuts and different cutting strategies on the stability and the machining time are examined with various case studies.