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2801 |
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Machine Tool Performance Requirements Associated with Modulated Tool-path Chip Breaking |
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Control of Precision Machines and Processes |
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| Content |
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Turning operations that involve ductile materials frequently generate long, stringy, chips that present a hazard to both the machinist and the machine tool. In addition, the post-machining handling of stringy chips is also a potentially dangerous and often expensive endeavor. While a variety of chip-breaking techniques are available, they generally depend on a mechanism for increasing the bending of the chip or the introduction of a one dimensional vibration that produces an interrupted cutting pattern. Unfortunately, neither of these approaches is particularly effective when making a “light depth-of-cut” on a contoured workpiece. This paper discusses a research project involving the Y-12 National Security Complex (Y-12) and the University of North Carolina at Charlotte (UNCC) in which unique, oscillatory part programs are used to continuously create an interrupted cut that generates pre-defined, user-selectable chip lengths.
The modulated tool-path chip breaking technique uses an oscillatory motion along the machining tool path that intermittently engages and disengages the cutting tool from the workpiece. This motion produces irregular waves in the “cut face,” while moving back and forth across the surface-texture scallops created by the turning process. The relationship between the spindle speed and the oscillation frequency determines the length of the chips that are created. It has been demonstrated that relatively small changes in spindle speed or oscillation frequency are sufficient to create the phase shift needed to produce either continuous of broken chips for a particular workpiece diameter. In addition, a model has been developed that allows the user to determine the process parameters needed to obtain a particular chip length, as well as define the modifications in either the spindle speed or the oscillation frequency needed to maintain the chip breaking action as the tool position changes with respect to the spindle centerline.
The experiments conducted to date have demonstrated the viability of the modulated tool-path chip breaking technique; however, there is still a significant amount of work to be done in order to provide a “production-ready process” that takes into account the desired workpiece attributes and process throughput, as well as the necessary machine tool/control system characteristics and the part programming requirements. This paper presents the results of machine characterization activities that are intended to lead to a model that allows a user to determine the machine performance requirements associated with specific workpiece characteristics and quality parameters. Other topics of interest include enhanced process models, an assessment of the resulting cutting tool and machine wear, an evaluation of the impact on the material properties of the part, and the thermal effects/benefits associated with the interrupted cut. |
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