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Dynamics of milling flexible structures

University of British Columbia

Peripheral milling of aerospace parts takes a considerable amount of manufacturing time on production floors. Recently, due to fatigue constraints and advances in high speed machining, aircraft components are machined as monolithic parts from solid blanks. This thesis focuses on the mathematical modeling of peripheral milling of aerospace parts with thin walls. The varying dynamics along the contact length of both the part and the cutter are considered. The structural dynamics of a flexible thin web and of the end mill are modelled as discrete models, whose modal parameters are identified experimentally. The kinematics of peripheral milling is modelled in the time domain. The chip removed at any point along the workpiece/ cutter contact length is predicted, including the influence of structural dynamic displacements of both the cutter and the workpiece at present and previous tooth passing intervals. The cutting forces are predicted as being proportional to the time varying dynamic chip loads. The time domain model of the process includes various non-linearities in the process such as the separation of the tool from the workpiece due to excessive vibrations. The time domain algorithm can predict the cutting load distribution on both cutter and thin web structures, dimensional surface finish of the part, vibrations, torque, power and bending load experienced by the lower spindle bearing of the machine tool. The predictions are verified experimentally by conducting numerous cutting tests. The accurate time domain simulations of dynamic milling have shown that large feed rates affect the chatter stability at low cutting speeds. This phenomenon has not been previously reported in the literature. An analytical model of the dynamic milling system with the influence of feed on the regenerative phase shift has been developed, and the stability of the system is solved analytically in the frequency domain. The developed time domain simulations of the process support the linear analytical solution. The mathematical models and algorithms developed in this thesis have been experimentally verified and have been used in peripheral milling of aircraft wing components in industry.

Thesis/Dissertation

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2009-05-20

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http://hdl.handle.net/2429/8012

Mechanical Engineering

University of British Columbia

UBCV

DSpace