Abstract: A tightening method yielding a precise control of the resulting clamping force, in which the tightening operation is performed in two steps, and the stress level is always kept within the limits of the elastic portion of the stress×strain curve. The method employs a single or multi-spindle power wrench controlled by a computer, provided with measuring means for the precise sensing of applied torque and turn angle in real time. The method comprises in a preferred embodiment a first and a second tightening operations, the data collected during the first operation being inputted to the computer which calculates the amount of torque to be applied to the fastener in the second and final tightening operation according to an algorithm which also comprises checking steps to ascertain that the results fall within the preset values, tolerances and scatter limits.

Abstract: A tightening method yielding a precise control of the resulting clamping force, in which the tightening operation is performed in two steps, and the stress level is always kept within the limits of the elastic portion of the stress×strain curve. The method employs a single or multi-spindle power wrench controlled by a computer, provided with measuring means for the precise sensing of applied torque and turn angle in real time. The method comprises in a preferred embodiment a first and a second tightening operations, the data collected during the first operation being inputted to the computer which calculates the amount of torque to be applied to the fastener in the second and final tightening operation according to an algorithm which also comprises checking steps to ascertain that the results fall within the preset values, tolerances and scatter limits.