Finite Element Simulation of Process Control for Bolt Tightening in Joints With Nonparallel Contact

In this paper, 3D finite element analysis (FEA) is used to simulate and evaluate different process control methods that are commonly used for automating the assembly of bolted joints in a mass production environment. The finite element (FE) model takes into account the thread helix angle of a fastener along with parallel and nonparallel contact surfaces under the bolt head. 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 the target torque at which the tightening process is automatically stopped. On the other hand, a torque-turn or torque-angle method is simulated by first applying a low level (threshold) torque, to the bolt head, followed by turning the bolt head by a specified angle of turn in order to achieve the desired bolt tension. The effect of variables such as thread and underhead bearing friction coefficients and bolt hole clearance is investigated. The FEA simulation provided in this study would be helpful in developing a reliable tightening strategy for joints with nonparallel bearing surfaces.