Determination of material properties for use in FEM simulations of machining and roller burnishing.

摘要

In machining, Finite Element Method (FEM) simulation is used widely to analyze the effect of process conditions and tool edge design upon cutting variables. Thus, it is possible to investigate material machinability, process economics, and surface quality. One of the most crucial inputs in performing a reliable FEM simulation is the availability of material plastic properties. Special material testing methods are required to consider the high ranges of plastic strain, strain rate and temperature that occur in practical machining conditions (for strain rates up to 106 s-1 and temperatures up to 103 °C). Conventional material testing methods are not suitable.; Roller burnishing is a surface finishing process where a ceramic ball (3-12 mm in diameter) freely rolls on the machined surface under a high pressure and flattens the roughness peaks. The ball is hydrostatically supported and lubricated by the pressure fluid. The process improves surface finish, increases microhardness and induces compressive residual stresses on the surface. To implement FEM simulation of roller burnishing process, the flow stress properties of the machined surface layer must be known. Such surface layer properties could be significantly different from the substrate (bulk) material due to severe plastic deformation and possible phase transformation caused by prior machining operations. In this study, two approaches to determine the flow stress data are proposed.; (a) The orthogonal slot milling tests to determine the flow stress at high strains, strain-rates and temperatures. (b) An inverse analysis in conjunction with the ball indentation test to determine the flow stress at the surface layer of a part but at low strain rates and room temperatures.; Furthermore, 2D and 3D FEM models were established by considering the flow stress properties obtained from the proposed procedures in order to analyze two problems: (1) effect of tool edge preparation and flank wear on burr formation in face milling of an aluminum alloy and (2) effect of roller burnishing parameters upon surface finish and residual stresses. Results from FEM simulations were compared and validated with the experimental data.