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UBC Theses and Dissertations

Mechanics and dynamics of the tool holder-spindle interface Namazi, Mehdi

Abstract

This thesis presents a general method for identifying and modeling the tool holderspindle interface in machine tools, using an experimental technique and the finite element method. The spindle assembly is one of the weakest parts in the machine tool and contributes to the chatter vibrations. The unwanted vibrations lead to a poor surface finish and can damage the tool, tool holder and spindle bearings. The tool holder-spindle interface is the connection closest to the cutting, and its dynamics can affect the stability of the cutting process and the dimensional accuracy of the work-piece. In this thesis, Timoshenko beam elements are used to model the tool holder, and an experimental setup is used to identify the contact stiffness of the interface for CAT and the HSK tapers. The finite-element models of the tool holder and the spindle are coupled through a receptance coupling model. The effect of the drawbar force is investigated as the main factor affecting the dynamics of the interface. It is shown that with an increase in the drawbar force, the dynamic stiffness of the connection between the holder and spindle taper decreases and saturates after a certain force level. The dynamics of various tool holder types is also investigated in the setup as a guideline to select tool holders for lowspeed and high-speed milling operations. This thesis also presents the coupling of tool holder dynamics identified through the finite element method with the experimentally identified spindle. The structural dynamics of the spindle with a tool-holder taper is identified experimentally through an inverse receptance coupling technique. The tool holder stick-out and tool are assumed to be a lightly damped linear structure, and its analytically predicted dynamics is coupled to the spindle with the aid of a receptance coupling method. This approach greatly reduces the number of impact modal tests needed to identify the dynamics of the machine at the tool tip after each tool change. The dynamics of the machine tool and the properties of the work-piece material are used to calculate chatter stability lobes. The proposed method is applied on a horizontal machining center and verified experimentally.

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