Controlling deformation and microstructure on machined surfaces

The deformation history and state of machined surfaces in low-speed cutting of metals with sharp, wedge-shaped tools have been characterized using high-speed image analysis, complemented by hardness and microstructure study. Large surface and subsurface strains are observed, and have been shown to arise from the severe plastic deformation intrinsic to chip formation. The deformation history of the chip and the near-surface region during the process of surface generation are found to be equivalent. The dependence of surface and subsurface deformation on parameters such as tool rake angle and undeformed chip thickness has been explored. The subsurface strain distribution is shown to scale with undeformed chip thickness (self-similarity), and to be influenced by the rake angle. Based on the observations, and process–deformation–microstructure correlations, a framework is developed for directly engineering surfaces with controlled deformation levels and microstructures by machining. The results also offer scope for enhanced validation of machining simulations and future development of multiscale models of machining.

► Deformation, strength and microstructure of machined surface are characterized.
► Deformation of the chip and the machined surface are found to be quite similar.
► Subsurface deformation scales with undeformed chip thickness.
► A framework is developed for controlling surface deformation and microstructure.