Xianyan Zhou

Geometric correction processes contribute to zero-defect manufacturing for improved product quality. Thin-walled metallic components are widely used in numerous applications such as electric vehicles and aircraft due to the lightweight feature, facilitating to achieve zero-emission goals. However, many components suffer geometric imperfections and inaccuracies such as undesired curvatures and twists, seriously affecting subsequent manufacturing operations, for example, automatic welding and assembly. Geometric correction techniques have been established to address these issues, but they have drawn little attention in the scientific community despite their wide applications and urgent demands in the industry. Due to the strict geometric tolerances demanded in high-volume automated production, it is urgent to increase the knowledge needed to develop new techniques to address future industrial challenges. This review paper presents an overview of typical geometric defects in thin-walled components and clarifies the associated underlying generation mechanisms. Attempts have also been made to discuss and categorize geometric correction techniques based on different forming mechanisms. The challenges in correcting complex thin-walled products are discussed. This review paper also provides researchers and engineers with directions to find and select appropriate geometric correction methods to achieve high geometric accuracy for thin-walled metallic components.

Review Lightweight Materials in Electric Vehicles Xianyan Zhou 1,*, Jun Jiang 2, Zhili Hu 3, and Lin Hua 3 1 Department of Mechanical and Industrial Engineering, Norwegian University of Science and Technology (NTNU), 7491 Trondheim, Norway 2 Department of Mechanical Engineering, Imperial College London, Exhibition Road, London, SW7 2AZ, UK 3 School of Automotive Engineering, Wuhan University of Technology, Luoshi Road, Wuhan, 430070, China * Correspondence: xianyan.zhou@ntnu.no Received: 23 September 2022 Accepted: 21 November 2022 Published: 18 December 2022 Lightweight materials are highly demanded in electric vehicles (EVs) to reduce environmental impacts and energy consumption. Aluminium alloys are promising materials in EVs due to their advantages such as high specific strength, corrosion resistance and recyclability. However, forming complex-shaped thin-wall aluminium products is challenging due to their poor formability and limited dimensional accuracy. Meanwhile, recycling some of the high-strength aluminium alloys from EVs is still challenging. This review highlights some of the future potential aluminium forming techniques for EV production, including incremental sheet forming (ISF), hot forming and quenching (HFQ ® ) technique, and transverse stretching and local bending (TSLB). Also, the issues associated with aluminium recycling are listed and discussed. This review provides scientific guidance to the industry and the scientific community for advancing the applications of aluminium alloys in EVs.

Dimensional accuracy of incoming components is crucial for automated welding and assembly in mass volume production. However, thin-walled extrusions made to industrial standards show severe dimensional variations, including gap opening, sidewall inclination, local convexity, and so on. Thus, one major challenge is to provide a low-cost correction method to improve the dimensional accuracy at a level demanded by automated assembly and/or product fit-up. A novel correction method called transverse stretch and local bending (TSLB) has recently been developed, enabling one to efficiently correct the dimensional deviations in thin-walled, U-channel profiles at a low cost. However, the lack of in-depth understanding of the underlying mechanism makes it challenging to efficiently optimise and control the process. In this study, the feasibility of this new technique was experimentally validated by four groups of TSLB tests with different profile dimensions, showing a dimensional accuracy improvement of about 92% compared with the as-received parts. The evolution of the critical dimensional characteristics, including gap opening and bottom convexity, is analysed numerically throughout four stages consisting of inserting, releasing, calibration, and springback. It is found that the inserting stage greatly reduces the dimensional deviations in a pure bending state, while the calibration stages further minimise the deviations in the bending and transverse stretching combined state. In addition, the wedge angle of the tool is found to be critical to the dimensional accuracy improvement. The low wedge angle facilitates the correction of sidewall inclination and gap opening, while the high wedge angle contributes to mitigating bottom convexity. The overall outcome of this study enhances the fundamental understanding of the effects of in-process stretching and local-bending on the dimensional capabilities of U-channel extrusions. This can ultimately generate guidelines that will lead to new application areas of aluminium extrusions in highly competitive marketplaces.

Central cracking in cross-wedge-rolled workpieces results in high wastage and economic loss. Recent cross-wedge rolling tests on two batches of steel showed that one batch formed central cracks, while the other was crack-free. The batches were both nominally of the same chemical composition and thermomechanical treatment history. In addition, both batches had passed all the standard quality assessments set for conventional forging processes. It was suspected that the different cracking behaviours were due to differences in microstructure between the two as-received steel billets, and the material in cross-wedge rolling (CWR) was more sensitive to the initial microstructure compared with other forging processes due to its specific loading condition including ostensibly compression and large plastic strain. Nevertheless, no previous study of this important problem could be identified. The aim of this study is, therefore, to identify the key microstructural features determining the central crack formation behaviour in CWR. The hot workability of the as-received billets was studied under uniaxial tensile conditions using a Gleeble 3800 test machine. Scanning electron microscope with energy-dispersive X-ray spectroscopy and electron backscatter diffraction was applied to characterise, quantitatively analyse, and compare the chemical composition, phase, grain, and inclusions in these two billets, both at room temperature and also at the CWR temperature (1080 °C). Non-metallic inclusions (oxides, sulphides, and silicates) in the billets were determined to be the main cause of the reported central cracking problem. The ductility of the steels at both room and elevated temperatures deteriorated markedly in the presence of the large volumes of inclusions. Grain boundary embrittlement occurred at the CWR temperature due to the aggregation of inclusions along the grain boundaries. It is suggested that a standard on specifying the inclusion quantity and size in CWR billets be established to produce crack-free products.

To cope with the problems of energy shortage and environmental pollution caused by the large number of retired cars, the energy efficiency of shredding recycled car bodies urgently needs to be improved. Before shredding, recycled car bodies are always cut into shaped metal plates and piled in several sheets like sandwich plates. Currently, the lightweight design philosophy has driven the widespread application of multi-materials in car bodies. In this study, the finite element and experimental methods are used to analyse the shredding process of multi-material plates from recycled car bodies in order to determine the characteristics of plates with different thicknesses and materials. The results showed that the shredding efficiency of steel laminates with less than three sheets is quite low although the efficiency can be raised by increasing the thickness. The shredding energy efficiency is higher for Al alloy laminates than for steels. The shredding energy efficiency can be improved by raising the strength of the shredding material. The results of this study proved that the shredding energy consumption can be reduced by shredding the different materials of the multi-material boards separately.