An Experimental Method to Determine the Minimum Uncut Chip Thickness (hmin) in Orthogonal Cutting

Chip formation has been studied for more than a century using, initially, process description followed by experimental procedures and mathematical models. At first, cutting edges were modelled as perfectly sharp, but real cutting tools contain small radius. Some of them are as low as few micrometers. Micro-machining operations often need uncut chip thickness (h) lower than edge radius. In such conditions a minimum value (hmin) may be found, under which material may not be properly removed. There is an extensive range of values for hmin in literature, as a percentage only of the edge radius (re). The criterion for establishing hmin also extensively varies as well as the cutting conditions used. The present work proposes an innovative method to study hmin with realistic values of cutting and feed speed (vc and vf) in orthogonal cutting. Using the proposed method several edges were tested and two of them, one sharp (re = 6 μm) and one blunt (re = 120 μm), are here presented in 3 different conditions. Values of hmin were detected for each of the cutting conditions. They were found to depend on the cutting conditions, on the maximum hmax established and on the way it grows during the interaction between edge radius and workpiece material. It was also suspected that BUE can be formed in front of the tool, depending on the way the uncut chip thickness increases during the interaction. The method also proved to be capable of detecting hmin and several other associations with the main parameters affecting that minimum value.