Tatsuya Sugihara

Title: Special Issue on Recent Progress in Precision Engineering | Author: Toshiyuki Enomoto and Tatsuya Sugihara

Adsorbed monomolecular organic films are shown to embrittle ductile metals via an induced surface stress.

In the cutting of Ti-6Al-4V alloy, the cutting speed is limited as a high cutting temperature leads to severe tool wear and short tool life, resulting in poor production efficiency. However, some recent literature has reported that various beneficial effects can be provided by forming micro-textures on the tool surface in the metal cutting process. In this study, in order to achieve high-performance machining of Ti-6Al-4V, we first investigated the mechanism of the tool failure process for a cemented carbide cutting tool in high-speed turning of Ti-6Al-4V. Based on the results, cutting tools with micro textured surfaces were developed under the consideration of a cutting fluid action. A series of experiments showed that the textured rake face significantly suppresses both crater wear and flank wear. In addition, optimum texture structures and the mechanism of the texture effects in high-speed machining of Ti-6Al-4V alloy were discussed.

We study deformation patterns in wedge indentation of annealed metals (e.g., copper) using high-resolution, in situ imaging and image correlation. Based on attributes of the deformation such as velocity fields, grid distortion and strain distributions, we discriminate between two modes of deformation — a cutting mode with narrow-angle (sharp) wedges, e.g., apex angle of 30°, and a radial-compression mode with wide-angle (blunt) wedges, e.g. apex angle of 120°. The cutting mode is characterized by significant material flow parallel to the wedge face; and a thin region of very high strain (∼3), that is located immediately adjacent to the indenter face (wall-layer), and arises from friction-induced deformation. The radial-compression mode is distinguished by material flow normal to and away from the indenter face, with negligible velocity component parallel to the indenter face. The corresponding strain field is one of bulk deformation, with the highly-strained region (strain ∼1) being of semicircular shape that extends from near the edge of indenter contact at the specimen surface, to well below the indenter tip. The observations show that indenter wall friction is likely to have a major influence on the deformation field only with narrow-angle indenters.Based on the observations of material flow, a suggestion is made (and validated) as to how the challenges faced in computational modeling of narrow-angle wedge indentation can be overcome. Implications for use of narrow-angle wedge indentation to study tribology of metalworking contacts, and ductile failure and damage in metals, are briefly discussed.

Metals such as Cu, Al, Ni, Ta, and stainless steels, despite their softness and ductility, are considered difficult to machine. This is due to large cutting forces and corresponding formation of a very thick chip during cutting, and hence, these metals are referred to as “gummy.” Their poor machinability of these materials arises because of an unsteady and highly redundant mode of plastic deformation referred to as sinuous flow. The prevailing plastic deformation mode during machining can be overcome by the application of certain coatings and chemical media on the undeformed free surface of the workpiece ahead of the cutting process. Using in situ imaging and concurrent force measurements, we present two different mechanochemical routes through which these media can improve machinability. The first route, which requires chemicals that adhere to the metal surface, such as glues and inks, improves cutting by inducing a change in the local plastic deformation mode—from sinuous flow to one characterized by periodic fracture or segmented flow. The second route, which requires chemicals that can react with the workpiece to form a low-friction layer, changes the sinuous flow mode to a smooth, laminar one. Both routes decrease cutting forces by more than 50% with order of magnitude improvement in surface texture as characterized by measured roughness and defect density. The results suggest a broad range of opportunities for improving the performance of machining processes for many difficult-to-cut gummy metals.

We study plastic flow in the vicinity of an indenter-material interface in wedge indentation of aluminum using high speed in situ imaging and particle image velocimetry (PIV) analysis. Displacement and strain fields in the indentation zone are obtained at high-resolution for different indenter angles and two lubrication conditions. These fields can be used to demarcate essential features of the material flow phenomena. The deformed layers close to the indenter wall fit a classical boundary layer profile in the framework of a Bingham-solid. Equivalent Bingham viscosities and boundary layer scaling relations are obtained. The viscosity values appear to reflect the nature of the friction interaction at the indenter-material interface and can potentially be used as a discriminating parameter for evaluating contributions to deformation and dissipation arising from interface friction.