DAMPING OF SELF-OSCILLATIONS AT LATHE TURNING BY SOFTWARE MODULATION OF CNC MACHINE-TOOL CUTTING SPEED

The purpose of the paper is determination of the limiting capabilities of a modern CNC lathe by cutting speed modulation created by software and evaluation of the damping efficiency of workpiece self-oscillations within the limits of these capabilities. The literary sources are reviewed. Software modulation of the spindle speed is performed using the technical solution of Siemens based on the use of a timer. Experimental studies are carried out on a turning machining center of the DMG NEF 400 model with a Siemens 840D CNC stand. Parameters in the experiments are measured using a laser vibrometer Polytec OFV-505, a three-component dynamometer Kistler Type 9129AA, a profilometer Taylor Hobson Form Talysurf i200, a Servo Trace function built in the system of machine-tool numeric control, Dyno Ware and National instruments Lab View 2012 software. Conducted tests of the idle machine-tool at all combinations of the spindle speed and its modulation frequency allowed to find out that spindle inertia prevents the machine-tool from complete development of the given depth of modulation. The degree of this development is determined by the graphs in the space of technological parameters. Machine-tool capabilities considered, the authors carried out the experiments on damping the self-oscillations of a non-rigid workpiece by the modulated cutting speed. For specific processing conditions the modulation of the cutting speed reduced the level of self-oscillations and cutting force fluctuations by 20 times and treated surface roughness by 2 times. Conducted tests of the machine-tool provided the opportunity to specify the area of its rational use for damping of non-rigid workpiece self-oscillations by means of cutting speed modulation. Machine-tool ability of almost complete elimination of self-oscillations when operating within its capabilities has been proved experimentally.

self-oscillations, cutting speed modulation, depth and frequency of modulation, shaft turning

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