A new mechanical calibration strategy for U-channel extrusions

Abstract

The extrusion process of aluminum profiles introduces dimensional variations commonly exceeding the dimensional tolerance requirements for fit-up and assembly when using automated welding processes in the automotive industry. Improving dimensional accuracy of extrusions is challenging from both a technical and economical point of view. However, an alternative technical approach is to introduce fast and simple downstream processes, such as mechanical calibration, to achieve components or products with improved dimensional characteristics. In this paper, a new mechanical calibration strategy is proposed based on the principle of combining transversal stretching and local bending. The strategy is tested on a U-channel extrusion-which is a particularly challenging geometry for extrusions concerning dimensional accuracy. The overall objective is to improve gap opening variations on U-channels compared with as-extruded dimensional capabilities, especially in the case of alloys that are water quenched to obtain high strength and ductility. The study is also intended to serve as basis for future optimization of the mechanical calibration process. An experimental platform and die/tool system was developed, and finite element simulation was used as a research tool to reproduce and better understand the calibration process, thus further analyzing the mechanisms and deformation characteristics important to dimensional accuracy. The experimental results show that the mechanical calibration strategy has good potential to improve the dimensional accuracy of gap openings of U-channels by 90%. The study demonstrates that as-extruded profiles with tolerance limits exceeding the requirements of the final component can effectively be calibrated with the proposed method and hence used in high-volume manufacturing.

Deformation Characteristics in a Stretch-Based Dimensional Correction Method for Open, Thin-Walled Extrusions

“…The strain rate was controlled to be 0.02 mm/min. More details such as the sample geometry and stress-strain response are referred to in previous work [37]. The anisotropy effects were found to be insignificant by comparing the stress-strain curves of the samples cut along different directions (0 • , 45 • , and 90 • related to the extrusion direction).…”

“…In this study, the dimensional data on the middle section of the profile were recorded and used. More details about the measurement strategy can be found in [37].…”

“…Based on the above perspectives, there is an urgent industrial demand to develop a correction method capable of cost-effectively improving the dimensional accuracy of aluminium extrusions without demanding additional and expensive forming operations. Recently, a novel mechanical calibration method was developed specifically to correct the dimensional defects in complex open-type profiles, for instance, U-channels [37]. In this method, stretching is applied in the transverse direction of the profile to achieve high dimensional accuracy, as stretching associated with bending generates less springback than that in pure bending states [29].…”

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

“…Recently, a new mechanical calibration technique, named transverse stretch and local bending (TSLB), was proposed. It combines the mechanisms of stretching and bending, enabling high dimensional accuracy to a low-cost penalty [15]. The feasibility of this technique was assessed experimentally with complex U-shape extrusions [15].…”

“…It combines the mechanisms of stretching and bending, enabling high dimensional accuracy to a low-cost penalty [15]. The feasibility of this technique was assessed experimentally with complex U-shape extrusions [15]. The deformation mechanisms of stretching and bending were studied by finite element analysis (FEA) [6].…”