High Precision Nut Threading Using Real-Time Tapping Torques Monitoring

Abstract

With the increasing demand for safety and automatically locking nuts, it’s important to guarantee a consistent nut quality. Traditionally, a floating tapping machine has been used for high-speed production, but it has unstable thread quality because of the existing gap between the tap and nuts holder. To overcome this problem, a stable tapping machine must be considered for tapping high precision threaded nuts and the tapping process must be monitored in real-time for the internal threads quality to reduce the inspection time. First, this article used the relative movement between a nut and its tap to establish the dimensionless tapping material removal rate. Furthermore, for creating the tapping torque curve of a specific nut, a few nuts were tapped to obtain the maximum value and variation of the tapping torque at various tapping speeds. Then, based on the differences in the hole sizes, chamfer depths, and material nature, the quality assurance range can be constructed as a real-time monitoring model for high precision thread manufacturing. To demonstrate the feasibility of the proposed procedure, tapping for carbon steel, alloy steel, and titanium alloy nuts was performed and the monitored tapping torques matched the nut quality classification of Japanese Industrial Standards (JIS).