Finite Element Simulation of Process Control of Bolt Tightening for Joints With Non-Parallel Contact

In this paper, 3-D finite element analysis (FEA) is used for simulating and evaluating the various process control methods that are commonly used in the automated assembly of bolted joints. A joint model with non-parallel contact under the bolt head is used. The FEA model takes into account the thread helix angle of the fastener. Simulation includes the torque-only and the torque-turn process control methods for achieving a desired level of the bolt preload at initial assembly of the joint. The torque-only process control option is simulated by applying a target peak torque value at which the tightening process is stopped. On the other hand, a torque-angle method is simulated by first applying a low level (threshold) torque (to the bolt head) after which the bolt head (or nut) would be rotated by a specified angle of turn, in order to achieve the desired bolt tension. The effect of thread and underhead bearing friction coefficients as well as the hole size are investigated. The FEA simulation provided in this study would be helpful for developing reliable tightening strategies for joints with (as cast) non-parallel bearing surfaces.