Plastic deformation and chip formation mechanisms during machining of copper, aluminum and an aluminum matrix composite.

摘要

The present work aims to study the plastic deformation behaviour of selected workpiece materials during the chip formation process. A 6061 aluminum alloy, a C11000 commercially pure copper and a 6061-10vol.%Al2O3 particulate reinforced composite have been chosen to study their machining behaviour under the orthogonal cutting conditions. The following experiments have been performed. (1) For the machining tests, different cutting parameters have been chosen within normal cutting conditions. (2) Detailed metallographic investigations have been conducted on the chip formation areas, including the primary deformation and the secondary deformation zones as well as in the area under the machined surfaces. (3) The temperature rise during the cutting process has been measured and analyzed. The main experimental observations/results can be summarized as; (1) The shear angles vary between 0 and 90 degrees in the chip formation areas depending on the location. (2) Shear strains are calculated based on the measured values of the shear angles in all interested areas. (3) The stresses in the chip formation zone and secondary deformation zone as well as in the machined surface have been estimated by using the data from microhardness measurements. (4) The shear strain rates have been estimated from the cutting speeds and the widths of the shear bands in the chip formation areas. (5) During machining, voids are generated along the strain gradient. The coalescence of the voids leads to the formation of shear cracks near the free surface of the chip. (6) The formation of a built-up-edge has been observed when cutting the 6061-10vol.%Al2O3 composite, but not when cutting Cu and Al. The built-up-edge effects play an important role in determining the plastic deformation behaviour in chip formation process. (7) The rotation of the secondary reinforcement particles in severe plastic deformation areas has been observed. Fracture of the secondary reinforcement particles is hardly ever observed. (8) Temperature rise distribution maps have been created based on the shear strain and the stress data as well as the physical and thermal properties of the workpiece materials. (9) Tool failure has been observed during cutting of the 6061-10vol.%Al2O 3 composite. The failure mechanism has been analyzed on scanning electron microscope. (Abstract shortened by UMI.)Dept. of Electrical and Computer Engineering. Paper copy at Leddy Library: Theses u26 Major Papers - Basement, West Bldg. / Call Number: Thesis2000 .Z51. Source: Dissertation Abstracts International, Volume: 62-10, Section: B, page: 4739. Adviser: A. T. Alpas. Thesis (Ph.D.)--University of Windsor (Canada), 2001.