Development of Roll Tapping Machine Capable of Synchronized Control of Spindle Rotation and Feeding Speed

In the roll tapping process of nut manufacturing, the tapping process is controlled only by the feed force in many cases, and only few studies have specifically analyzed the effect of the feeding speed and the revolutions per minute (RPM) of the spindle. In this study, we developed and introduced a flexible roll tapping machine that synchronizes and controls nut feed speed and spindle RPM. The tapping process with the developed machine was analyzed through experiments and numerical analysis, while considering the variables of nut feeding speed and spindle RPM. The experiments conducted using the equipment demonstrated that the thread quality was optimal under precisely controlled process conditions with forming 1.0 pitch per revolution (pitch/rev). In addition, when the feeding speed was increased, a substantial increase in the reaction force was observed, even with the forming rate controlled at 1.0 pitch/rev. The validity of these experiments was further confirmed through finite element (FE) analysis. The FE simulation shows fairly good agreement with the trend of the experimental force–displacement curve for each process condition, and the average error between the experiments and the FE predictions is roughly 12.6%. The results of this study show that the developed equipment performs well in control by synchronizing the spindle RPM and nut feeding speed.