Study of Two-Stage Tightening of Threaded Fasteners Using Various Tool Speed Combinations

This paper investigates the effect of various tool speed combinations on the torque-tension relationship in a two-stage torque control process for the tightening of threaded fasteners. The tightening speed has a considerable affect on the thread and bearing friction coefficients. Hence, the amount of clamp load generated by a specified level of the tightening torque is significantly influenced by the tool speed combinations in many high volume applications. In two-stage processes, the fastener is first tightened to an intermediate torque level beyond which the tool speed is changed but the tightening is continued until the full target torque is reached. The effect of tightening speed combinations (for stages one and two) on the torque-tension relationship is investigated. Data on the coefficients of thread and bearing friction as well as the Nut Factor K is investigated. The findings of this study are helpful in predicting the clamp load generated in bolted joints, which enhance its reliability and safety. Additionally, the study provides helpful data that may be utilized for developing reliable assembly strategies in mass production applications such as the automotive industry.