Micro-Scale Characterization of Machining Interfaces

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The machining interface represents a situation where important phenomenological events occur over small spatial and short time scales. By combining various optical techniques with the use of transparent cutting tools; e.g., sapphire, diamond, it is possible to directly observe and analyze these events by magnifying their length and time scales. Having a visual record frequently gives clues to the physical processes taking place and is often advantageous in showing "what is and what isn't happening." The nature of contact along the tool-chip-work interfaces, and the temperature distribution at these contact zones, will be studied in a novel series of experiments using optically transparent tools, high-resolution optical microscopy, high-speed, CCD-based, multi-wavelength infra-red (IR) pyrometry and high-speed micro-photography. Preliminary observations show that a complete characterization of the contact boundary conditions (e.g. extent of sticking, sliding zones, etc.) and the first detailed map of the complete temperature and velocity distributions at these interfaces can be achieved with the use of these techniques. The effect of parameters such as cutting speed both in the conventional and high speed machining regime, tool geometry, tool wear, and tool coatings, on the contact conditions and interface temperatures is being explored. The experiments represent a natural and interesting evolution of previous in-situ observational work on the low speed cutting of metals. The contact boundary conditions and the interface temperature distributions are key parameters for validation and refinement of models of the mechanics of machining; for control of tool temperatures, tool wear and work surface quality; and for realizing the long sought after goal of complete predictability of the machining process.From a technological standpoint, the results of the research may be expected to have a major impact in enhancing the efficiency of machining processes, enabling the design of tools and coatings for reducing wear and reducing the application of fluids in machining.