Patent ID: 7958611

Claim:
A method for quality checking a screw joint tightening process at production tightening of a screw joint using a torque impulse wrench having a shut-off function to be set to interrupt torque impulse delivery as a desired screw joint pre-tension level is attained, comprising: tightening in a pre-production calibration process a number of screw joints identical to said screw joint using the impulse wrench to be used during production tightening; registering, during tightening of said number of screw joints, a scattering of values of at least one tightening parameter at attainment of the desired pre-tension level; forming a reference set-up including at least one statistically determined limit value based on the scattered values of the at least one tightening parameter registered at ends of the pre-production tightenings, the at least one limit value reflecting a correctly functioning impulse wrench and a correct screw joint; comparing the at least one limit value of the reference set-up with a value of the at least one tightening parameter actually obtained during the production tightening, and indicating an occurring discrepancy between the value of the at least one tightening parameter actually obtained during the production tightening and the at least one limit value of the reference set-up as an indication of at least one of a malfunctioning impulse wrench and a faulty screw joint.