Abstract: A method and apparatus for tightening an assembly including a pre-load indicating fastener is disclosed. Pre-load indicating fasteners are generally tightened until a crushable element, forming a portion of the pre-load indicating fastener, is plastically deformed. The present invention permits such fasteners to be tightened until the crushable element of the fastener is completely deformed. This reduces the problem of relaxation generally associated with such fasteners. The present invention permits joints including such fasteners to be tightened by automatic tightening systems, if so desired. The assembly is tightened until the crushable element of the fastener is fully plastically deformed and elastic deformation of the joint has commenced. Sensing means are provided in the automatic tightening system to enable detection of this point and to automatically stop the tightening system when this point is reached.

Abstract: A sequential tightening system is disclosed in this application for tightening a plurality of fasteners to a final predetermined condition and includes a plurality of wrenches for tightening the fasteners and a control system operatively associated with each of said wrenches for tightening the fasteners to a first predetermined condition, preferably their seated condition and at a relatively high output speed of the wrenches, and temporarily discontinuing the tightening procedure. When the tightening procedure of all of the wrenches has been temporarily discontinued, the control means restarts the tightening procedure of each wrench simultaneously or, if desired, sequentially, and, preferably at a lower output speed of the wrenches. As each wrench tightens its operatively engaged fastener to the final predetermined condition, the control means discontinues the tightening procedure of that wrench.