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Author

Farid Abrari

Date of Award

1998

Degree Type

Thesis

Degree Name

Doctor of Philosophy (PhD)

Department

Mechanical Engineering

Supervisor

Dr. M. A. Elbestawi

Co-Supervisor

Dr. A.D. Spence

Abstract

Multi-axis milling simulation of flexible parts is a highly interdisciplinary topic. It includes theories and methods in milling mechanics, structural mechanics and geometric simulation. In order to determine the acceptable cutting conditions, process planners faced with the flexible tools and thin walled structures either use very conservative cutting conditions, or in the case of high volume productions, trial and error methods. In either case, a final air cut is usually required to bring the machined surface within the tolerance. Although practicala, the above approach results in low productivity. Development of an analysis software capable of predicting the cutting forces deflections and surface errors in multi-axis milling of the thin wall structures is therefore highly desirable. By eliminating the need for trial and error methods a dynamic multi-axis process simulator can assist process planners to optimize the cutting condition and tool path for the least geometrical errors. This thesis describes such a simulator, implemented as an integrated CAD/CAM architecture consisting of both geometric and physical simulators. A static cutting force model is introduced which accounts for the rotation of the a and b axes in multi-axis side milling operations. The proposed formulation is based on a vectorial approach which reduced to a conventional formulation if a three-axis tool path is used. A dynamic multi-axis force model is also developed which is capable of modeling the tool/workpiece structural interaction. The dynamic response of the workpiece to the instantaneous cutting forces is modeled using a special finite element code. In conjunction with the finite element code, a solid based automatic mesh generation algorithm is also developed. The automatic mesh generator frequently updates the finite element mesh as the workpiece geometry changes. The dynamic parameters of the tool, experimentally found at its tip, are extrapolated for the rest of the cutter elements along the tool axis. The tool elemental parameters are then used to model the dynamic response of the cutter. Using the effective deflection of the tool/workpiece system, profile of the machined surface is simulated and its geometric deviation from the design surface is computed. This is highly desirable for side milling of ruled surfaces, where the value added is very high. For the experimental verification of the developed models, a twisted ruled surface was machined using a four-axis milling operation. The thickness of the twisted blade was reduced to 2.0 mm for the case of the dynamic cutting tests. The profile left on the machined surface was compared with the simulation result. In all comparisons a good agreement is seen between the experimental data and simulation results, which verifies the validity of the developed models and techniques.

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