Chip dynamics in diamond turning

An important concern in the machining of high quality, precision sur aces is the prevention of contact between the chips formed during the machining process and the finished surface. Since effective chip control requires an understanding of chip geometry, the direction of chip motion and the interaction between the chip and the physical mechanism used to control its motion, a study of all three areas has been completed. The examination of chip geometry focused upon machining parameters influencing chip radius of curvature. Cutting speed, chip cross-sectional geometry, workpiece hardness and workpiece modulus of elasticity were found to be of primary importance and were incorporated into a chip curvature parameter, chi, that was demonstrated to exhibit a power law relationship with chip radius of curvature for materials tested except lead. Work examining the directional characteristics of diamond turned chips in plated copper using nu-nose tools demonstrated that the important cutting parameters were geometrical in nature and included depth of cut, feed rate, tool geometry, tool orientation and tool path angle. Upon the completion of tests, experimental work was performed examining the use of air and oil streams to control chip motion. Despite difficulties in collecting low stiffness chips with a smaller cross-sectional area, optimal control with a vacuum system was observed using a small diameter nozzle located as close to the tool/workpiece interface as possible. More consistent and repeatable chip control, however, was demonstrated for both high and low stiffness chips using a large diameter, low velocity oil stream aimed from beside the tool, with the flow direction of the chip, such that the airflow generated by the rotating workpiece moved the oil stream away from the workpiece surface upon crossing the tool face. Although the addition of a vacuum system with the oil stream did not provide improved chip control, it did offer the added benefit of allowing the complete removal of chips from the machining area. Thus, keys to the removal of chips from the cutting zone have been identified and can be utilized to provide efficient and reliable chip control for diamond turning processes.