QUALITY EVALUATION OF BOLTED JOINTS USING TIGHTENING MONITORING AND SIMULATIONS
Résumé
This paper presents a method to control the quality of a bolted assembly through tightening monitoring. The idea of the method is to record both torque and angle during tightening, and to divide the tightening curve into several parts using the different changes of slope. Each part of the curve is related to a physical event occurring during the tightening. For example, two plates separated by a 0.15 mm gap are clamped using a 5.6 mm diameter bolt (fig 1 left). The corresponding tightening curve (fig 1 right) is divided into: a locking phase (1), gap reduction (2) and the actual tightening (3). Analysing these different parts allows the operator to check in real time if the gap between the parts is closed and if the contact surface is free of defects such as burrs or chips. Thus this method enables direct fastening without the disassembly phase after drilling and/or removes additional controls once the fastening has been done. First the method will be presented along with a full 3D finite element model (fig 2 left) used to understand and predict the phenomena for future studies. The model contains detailed geometry of the bolt, nut and their threads. The tightening of the joint is achieved through the rotation of the bolt and the contact between the threads. This model is evaluated using analytical model provided by the literature and preliminary tests on small coupons. These tests were carried out using one diameter but two different grip lengths. The method is then applied on a more representative industrial case thanks to a test bench with multiple bolts and thicknesses. It appears that the precision of the tightening machine is a key factor along with the stiffness of the plates to detect precisely the gaps between the parts.