Development of Vibration Diagnostic System for Improving Thread Machining Technology

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A vibration analysis method was newly proposed which was paied special attention to the synchronous error between rotational motion of a workpiece and straight feed motion of a cutting tool, which directly caused lead error of a machined thread. The method was demonstrated on a threading machine and a thread grinding machine. The results are summarized as follows :1. A new vibration analysis method for thread cutting consists of torsional static characteristic test, torsional dynamic characteristic test, intermittent cutting test, idle running test and thread cutting test.2. By applying torsional dynamic characteristic test by impulsive cutting, torsional natural frequency between a cutting tool and a workpiece can be obtained. The torsional natural frequency can be identified by intermittent cutting test.3. Synchronous error which was recorded during idle running and thread cutting was processed by an FFT ( fast Fourier transform ) analyzer. By consulting a schematic drawing of a rotational transmission mechanism which is contained in a tested threading machine, specific parts can be revealed which cause a lead error of a machined thread based on frequency components of synchronous error processed by an FFT analyzer.4. A new vibration analysis method for thread grinding consists of idle running test, rapidly stopping test and thread grinding test.5. After synchronous error during idle running and thread grinding was processed by the same manner as the case of threading machine, specific parts can be revealed which cause a lead error of a ground thread. In the case of a tested thread grinding machine, it was ascertained that a lead screw for driving a traverse table mainly caused a lead error during one pitch which was remarkably recognized by lead error measuring test.6. A newly proposed vibration analysis method for thread cutting and thread grinding can be effectively applied to diagnose other thread production equipments which are used in many machine shops.