Thomas A. Dow

Bio: Thomas A. Dow is an academic researcher from North Carolina State University. The author has contributed to research in topics: Diamond turning & Machining. The author has an hindex of 19, co-authored 54 publications receiving 2496 citations.

Review of vibration-assisted machining

Abstract: Vibration-assisted machining (VAM) combines precision machining with small-amplitude tool vibration to improve the fabrication process. It has been applied to a number of processes from turning to drilling to grinding [9] , [36] . The emphasis on this literature review is the turning process where VAM has been applied to difficult applications such as diamond turning of ferrous and brittle materials, creating microstructures with complex geometries for products like molds and optical elements, or economically producing precision macro-scale components in hard alloys such as Inconel or titanium. This review paper presents the basic kinematic relationships for 1D (linear vibratory tool path) and 2D VAM (circular/elliptical tool path). Typical hardware systems used to achieve these vibratory motions are described. The periodic separation between the tool rake face and uncut material, characteristic of VAM, is related to observed reductions in machining forces and chip thickness, with distinct explanations offered for 1D and 2D modes. The reduced tool forces in turn are related to improvements in surface finish and extended tool life. Additional consideration is given to the intermittent cutting mechanism and how it reduces the effect of thermo-chemical mechanisms believed responsible for rapid wear of diamond tools when machining ferrous materials. The ability of VAM to machine brittle materials in the ductile regime at increased depth of cut is also described.

Tool force and deflection compensation for small milling tools

Abstract: A technique to compensate for deflection of small milling tools (diameter < 1 mm) has been demonstrated. This open-loop technique involves predicting the cutting and thrust forces, applying these forces to the tool, calculating the shape error due to tool deflection and creating a new tool path to eliminate this error. The tool force model has evolved from a decade of research to predict the forces in diamond turning. This model was modified to include the effects of tool rotation in milling as well as the changes in contact area and force direction using a ball end mill to create a free form surface. Experimental measurements were made to corroborate the components of the tool forces in the cutting and thrust directions. The force model was then combined with tool stiffness to calculate the deflection of the tool as a function of the depth of cut, the up-feed per revolution and the geometry of the part. Two experiments were used to demonstrate the effectiveness of this error compensation technique-a slot and a large circular groove. Each experiment reduced the error due to tool deflection by an order of magnitude from 20-50 μm to 2-5 μm.

Application of a fast tool servo for diamond turning of nonrotationally symmetric surfaces

Abstract: The fabrication of nonrotationally symmetric surfaces by diamond turning requires tool actuation at a bandwidth significantly higher than the rotational frequency of the surfaces. This requirement cannot be met by standard slide drives due to their large mass and consequent low natural frequency. This articles describes the development of a laboratory-scale diamond-turning machine with piezoelectric-driven fast tool servo. The capability of this apparatus will be demonstrated for high-speed features such as sine wave, square wave, and ramp-shaped surfaces. Also described is the implementation of this fast tool servo on a commercial diamond-turning machine. Several nonrotationally symmetric surfaces have been machined, and their images are included.

Investigation of micro-cutting operations

Abstract: The miniaturization of machine components is perceived by many as a requirement for the future technological development of a broad spectrum of products. Miniature components can provide smaller footprints, lower power consumption and higher heat transfer, since their surface-to-volume ratio is very high. To create these components, micro-meso-scale fabrication using miniaturized mechanical material removal processes has a unique advantage in creating 3D components using a variety of engineering materials. The motivation for micro-mechanical cutting stems from the translation of the knowledge obtained from the macro-machining domain to the micro-domain. However, there are challenges and limitations to micro-machining, and simple scaling cannot be used to model the phenomena of micro-machining operations. This paper surveys the current efforts in mechanical micro-machining research and applications, especially for micro-milling operations, and suggests areas from macro-machining that should be examined and researched for application to the improvement of micro-machining processes.