In the current research, an analytical chip formation model and the methodology to determine material flow data have been developed. The efforts have been made to address work hardening and thermal softening effects and allow the material to flow continuously through an opened-up deformation zone. Oxley's analysis of machining is extended to the application of various engineering materials. The basic model is extended to the simulation of end milling process and validated by comparing the predictions with experimental data for AISI1045 steel and three other materials (AL-6061, AL7075 and Ti-6Al-4V) from open literatures.
The thorough boundary conditions of the velocity field in the primary shear zone are further identified and analyzed. Based on the detailed analysis on the boundary conditions of the velocity and shear strain rate fields, the thick “equidistant parallel-sided” shear zone model was revisited. A more realistic nonlinear shear strain rate distribution has been proposed under the frame of non-equidistant primary shear zone configuration, so that all the boundary conditions can be satisfied.
Based on the developed model, inverse analysis in conjugation of genetic algorithm based searching scheme is developed to identify material flow stress data under the condition of metal cutting.
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On the chip-tool interface, The chip-tool interface is assumed to consist of the secondary shear zone and elastic friction zone(i.e. sticking zone and sliding zone). The normal stress distribution over the entire contact length is represented by a power law equation, in which the exponent is determined based on the force and moment equilibrium. The shear stress distribution for the entire contact length is assumed to be independent of the normal stress. The shear stress is assumed to be constant for the plastic contact region and exponentially distributed over the elastic contact region, with the maximum equal to the shear flow stress at the end of sticking zone and zero at the end of total contact. The total contact length is derived as a function governed by the shape of normal stress distribution. The length of the sticking zone is determined as the distance from the cutting edge to the location where the local coefficient of friction reaches a critical value that initiates the bulk yield of the chip. Considering the shape of the secondary shear zone, the length of the sticking zone can also be determined by angle relations. The maximum thickness of the secondary shear zone is determined by the equality of the sticking lengths calculated by two means. With an arbitrary input of the sliding friction coefficient, various processing parameters as well as contact stress distributions during orthogonal metal cutting can be obtained. / UOIT
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:OOSHDU.10155/234 |
| Date | 01 April 2012 |
| Creators | Pang, Lei |
| Contributors | Kishawy, Hossam A. |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | Dissertation |
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