Integrated process design of Al6061 alloy bolts for fastening offshore platforms

In this study, we design an integrated manufacturing process for Al6061 alloy bolts to fasten offshore platforms. The proposed scheme includes the theoretical design and numerical study for the heading, trimming, and thread-rolling process. For the theoretical design, the initial rod diameter and the penetration depth (PD) in the thread-rolling process are calculated according to thread standards and geometric relation. The dimensions of the initial workpiece for the heading process are obtained using the volume constancy law. Considering process limitations to predict the defects, the number of stages is set, and the preform is then determined using the design rule in the heading process. Based on the theoretical design, finite-element (FE)-analysis is conducted. In order to predict the defects and fracture phenomena, the ductile fracture criterion was applied during the heading and trimming processes. The Taguchi method is used to optimize the trimming and thread-rolling process with the set of design parameters, such as the PD, transfer velocity, and revolutions per minute in the thread-rolling process, and the blade radius (BR), land width, and stop distance in the trimming process, respectively. Results show that the PD and BR have the most significant effect on the dimensional accuracy and forming load. To validate the proposed design, the aluminum alloy bolt-forming experiment is performed. We obtain the sound Al6061 alloy M12 hexagonal bolt shaped with highdimensional accuracy. Therefore, this research provides valuable guidelines for the design of the integrated forming process in actual bolt production.