Effect of Warm Forming on Formability and Springback of Aluminum Alloy Brazing Sheet

Abstract

Abstract. This paper investigates the effect of warm forming (up to 350⁰C) on the formability and springback behavior of AA3003/AA4045 brazing sheet (0.2 mm gauge) for two temper conditions: Oand H24-temper. The key objective is to utilize warm forming to form aggressive geometries and control the springback to improve the part flatness which enables the use of harder temper material with improved strength. Simulations and experiments are performed considering heated dies at several different temperatures up to 350 °C and the blanks are pre-heated in the dies. The geometry under study is referred as a surrogate heat-exchanger component (SHC) and contains complex features found on commercial automotive thermal management systems. An in-depth springback characterization was completed for a wide range of forming process parameters such as: temperature, punch load, sheet direction, and holding time. Numerical simulations were also performed to predict the springback behavior and were compared to the experiments. There were no clear results showing improvement in formability using the warm forming process. However, increased temperatures (above 250 ⁰C) offered significant improvement in springback for the harder H24 material temper. IntroductionWith more strict regulations on fuel economy and emissions, the automotive industry is being pushed towards electric and hybrid electric vehicles (EVs and HEVs) that require effective thermal management systems. Currently, battery cooling plates are manufactured using aluminum alloy brazing sheet in the O-temper condition to enable higher formability and reduce springback. Harder sheet tempers, such as H24 for example, are desirable due to greater ease of handling and strength; however, these harder tempers often have lower formability and higher springback.One approach to improving formability of aluminum alloy sheet is through use of warm forming techniques. Numerous studies have reported increased formability for 5000-series alloys due to the reduced stresses and increased strain rate sensitivity operating at temperatures in the 200-300 °C range [1][2][3]. Studies of warm forming of 3000-series aluminum are more limited, notable exceptions being Abedrabbo et al. [4] who demonstrated increased formability at elevated temperatures for AA3003 sheet and more recent studies by Bagheriasl et al. [5,6] who characterized the increase in forming limit of 0.5 mm brazing sheet used in automotive heat exchangers (radiators).Warm forming has also been shown to reduce springback in aluminum alloys [7][8][9], largely through a reduction in operative stresses during forming. Verma et al. [10] studied the effect of temperature and temper condition on springback in u-channels fabricated from 0.2 mm brazing sheet, the focus of the