Finite element simulation of a metal forming process & die design

Abstract

Thread Rolling (also known as roll threading) is a cold forming process for producing threads or other helical or annular forms on a fastener. This is achieved by rolling the surface profile of hardened steel dies onto the surface of a cylindrical or conical blank. Dies for Thread Rolling may be either flat or cylindrical. In contrast to thread cutting and thread grinding, thread rolling does not remove any metal from the workpiece. However this feature does not mean that threads are formed perfectly. Since the early days of thread rolling defects have been accepted as part and parcel of the thread rolling process. The objective of this study was to design a new Thread Rolling Die, which would significantly lower the occurrence of the aforementioned fastener defects, particularly internal ones. This design process was undertaken using a combination of advanced finite element techniques and experimental testing. Modifications to the "thread form" of the thread rolling die were considered the most appropriate means by which to alter the design of the standard thread rolling die. Numerous different thread rolling die designs were simulated and analysed using finite element analysis and an optimum die design was predicted. The optimum thread rolling die design was then produced by a thread rolling die manufacturer. A series of experimental trials using these new thread rolling die designs were carried out in the U.S.A. The occurrence of defects in the fasteners produced using the new die designs was checked. Tensile and fatigue tests of the new fasteners were also performed to ensure that the new thread rolling die designs had no detrimental effects on the mechanical properties of the fasteners. The results from these experimental trials confirmed the finite element predictions.