UBC Theses and Dissertations
Unified mechanistic identification of cutting force coefficients Mammadov, Bahram
The prediction of cutting forces is essential to plan machining operations without unstable vibrations, tool breakage, excessive tool deflections, and spindle overloads. Tool geometry, tool-workpiece engagement area, and material-dependent cutting force coefficients are required to model the cutting forces. This thesis presents a generalized mechanistic model to identify the friction and normal force coefficients between the chip and the rake face of the tool. The cutting force coefficients depend on the material’s shear yield stress, the friction coefficient between the workpiece and tool materials, the shear angle, local rake and oblique angles, cutting speed and chip thickness when machining isotropic metal alloys. They also depend on the flank wear, the direction and density of fibres, and the fibre-matrix layout for Carbon Fibre Reinforced Polymer (CFRP) composite materials. A generalized method that allows estimating the cutting force coefficients from milling and drilling tests is proposed in the thesis. The cutting force coefficients are estimated by modelling forces with differential elements as a function of the fibre angle, tool geometry, and process parameters using least squares. The distributed forces are superposed in the measured directions. In addition to tooth passing frequency, the cutting forces are considered periodic due to fibre direction and density, which is handled by modelling the cutting force coefficients by a mean and fundamental component governed by the fibre-cutting angle relative to the cutting speed. The effect of the tool wear is considered for CFRP drilling operations. The model has been extended to include the dependency of force coefficients on the normal rake angle when machining isotropic metal alloys. The proposed general mechanistic model is experimentally validated in the milling and drilling of unidirectional CFRP composite and Aluminium Al7050-T7451 materials. It is shown that the identified cutting force coefficients can be used to predict forces in any machining operation, as demonstrated in ball end milling and drilling tests. The model allows rapid but sufficiently accurate identification of cutting force coefficients for isotropic and anisotropic materials.
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