Mechanical Properties of Tightening Process of Bolted Joints by Impact Wrenches

The tightening method using impact wrenches is used rather frequently to clamp bolted joints requiring high workability. The tightening torque is applied in the form of impact forces generated by a rotating hammer, which is powered by compressed air, hydraulic force or electric power. The primary advantage of impact wrenches is that the tightening operation can be completed in a short time. However, the accuracy of the generated bolt force is not so high, because of the complicated mechanical behavior caused by the action of impact forces. In this paper, the tightening process of bolted joints by use of impact wrenches is studied from the mechanical point of view, and the relationship between the nut rotation angle and the repeat count of impact forces is formulated. Based on the foregoing results, a practical tightening guideline is proposed by considering the effects of joint stiffness and impact friction coefficient that vary in the progress of the tightening operation.