Numerical Analyses of Deformation Mechanisms in a Novel Dimensional Calibration Technique for Thin-Walled, Open Extrusions

Abstract

High dimensional accuracy is of crucial importance in digital manufacturing to guarantee production capability and product performance. For manufacturing of thin-walled complex extrusions, it is often challenging to meet the tight dimensional tolerance requirements for automated mass production, due to dimensional imperfections and variations accumulated from the thermo-mechanical processing history. Recently, a new calibration technique, called Transverse Stretch and Local Bending, was developed, enabling significant improvement of the dimensional accuracy of thin-walled open profiles at a low cost. However, the deformation mechanisms have not been well understood, which in turn affect the process design for achieving high-precision products. In this study, a through-process finite element model was established and experimentally verified, which is used as a tool to investigate the mechanisms in the calibration process. It is found that the gap opening is mainly reduced in the inserting stage, but the calibration stage plays a key role in achieving high-precision products after unloading. The critical factor to achieve high dimensional accuracy is reducing the through-thickness gradients on both the profile bottom and sidewall. By controlling the total vertical displacement in the transverse stretch and local bending, the stress gradients can be effectively reduced, and the dimensional deviation caused by springback after unloading can be well mitigated. This fundamental study will benefit the industry to obtain high-precision extrusions.