Metal cutting modeling

Metal machining involves two basic processes: chip creation and chip evacuation. These processes involve two basic physical mechanisms:

• plastic deformation within the chip ;

• contact with the tool.

The modeling of chip formation is based on an understanding of these two mechanisms, and aims to predict chip geometry, cutting forces and temperature rise on the basis of cutting conditions and the thermomechanical properties of the material being machined and the tool. In particular, it should help in the rational management of cutting data banks, and provide elements for assessing various practical problems:

• machinability of a material, i.e. its suitability for machining (forces required, chip length and shape, etc.);

• elastic deformation of the tool assembly – toolholder – machine-tool (article TI [33] );

• interpretation of tool wear and damage patterns (article TI [34] );

• surface quality of the machined part (roughness, work hardening, metallurgical structure, residual stresses).

Alternatively, a more modest objective can be set for this modelling, namely to use a number of relatively easy-to-measure quantities (chip thickness, cutting forces, for example) to deduce quantities that are more difficult to access, such as heating or the rheological and tribological characteristics of the material being machined.

The developments presented in this article take stock of the current state of knowledge and modelling. The presentation starts with the simplest analyses, which are purely mechanical, and then moves on to the finer, thermomechanical approaches, which provide a more realistic description of the physical phenomena involved in chip formation. We conclude with a brief overview of numerical simulation approaches using the finite element method, to illustrate the power of these potentially most comprehensive approaches, and to clarify their current limitations. In particular, we won't go into the precise description of the calculation algorithms used for this purpose, and will only comment on a few examples.

For the first two sections, we'll confine ourselves to the simple case of orthogonal cutting without an added edge, the only case actually dealt with by mechanical and thermomechanical models, and which highlights the main trends...