Sinuous Flow in Cutting of Metals

In the cutting of metal, central to countless manufacturing processes, the well-known and counterintuitive fact is that soft metals are much more difficult to cut than hard ones; very large forces are involved, and a poor surface finish is obtained. Grain-scale $i\phantom{\rule{0}{0ex}}n$ $s\phantom{\rule{0}{0ex}}i\phantom{\rule{0}{0ex}}t\phantom{\rule{0}{0ex}}u$ imaging reveals that when soft metal is cut, laminar flow is inherently unstable and material is removed instead via $s\phantom{\rule{0}{0ex}}i\phantom{\rule{0}{0ex}}n\phantom{\rule{0}{0ex}}u\phantom{\rule{0}{0ex}}o\phantom{\rule{0}{0ex}}u\phantom{\rule{0}{0ex}}s$ flow, a mesoscale mode involving repeated folding, with significant vortexlike components. These observations suggest control strategies with important performance benefits for manufacturing, as well as a need to reexamine the foundations of cutting and large-strain deformation at surfaces.