Patent ID: 6314817
Filing Date: 2001-11-13
Classification: B23P,B25B

Abstract:
A method for tightening a threaded fastener to a desired final axial load (N.sub.F) above a yield point (Y) of the fastener, said method comprising:detecting instantaneous values of applied torque, angular displacement (.PHI.) of the fastener, and travel time (.DELTA.t) of ultra-sonic waves induced in the fastener;detecting the yield point (Y) of the fastener as a significant change in a relationship between two tightening parameters, and detecting an ultra-sonic wave travel time (.DELTA.t.sub.Y) at the yield point (Y) of the fastener;determining the axial load (N.sub.Y) at the yield point (Y) of the fastener by comparing the ultra-sonic wave travel time (.DELTA.t.sub.Y) at the yield point (Y) of the fastener with a pre-established ultra-sonic travel time (.DELTA.t) in an unloaded fastener; andcontinuing tightening of the fastener into a plastic deformation region beyond the yield point (Y) of the fastener until the detected instantaneous value of the ultra-sonic wave travel time (.DELTA.t) reaches a level (.DELTA.t.sub.F) which according to a pre-tightening determined relationship between the ultra-sonic travel time (.DELTA.t) and an axial load (N) above the yield point corresponds to the desired final axial load (N.sub.F).