Proposition of Tightening Method with High Accuracy by Combining Torque and Angle Control Methods

Abstract

Torque control method is a commonly employed tightening method when clamping joint members with various configurations. However, it involves an essential problem that produces a fairly large scatter in bolt preloads. In contrast, elastic angle control method provides high accuracy of bolt preloads, though its tightening operation is rather complicated. In this study, by combining the foregoing two different methods, a new tightening strategy is proposed, which may achieve the high accuracy and easy operation simultaneously. The proposed method can estimate the critical value of “nut factor” during the tightening operation by torque control method, thereby changing the objective torque in the course of tightening operation in order to clamp the target bolt with high accuracy. A trial tightening equipment, which is manufactured based on the proposed principle, is found to tighten the target bolts with less than 9% of the bolt preload scatter.