Warm forming of thermoplastic fibre metal laminates

Abstract

Abstract. In this paper, the forming behaviour of sheet-like metal/polymer/metal (MPM) and thermoplastic fibre metal laminates (TFMLs) is introduced. TFMLs are based on thin metallic cover sheets and fibre-reinforced thermoplastic matrix (here polyamide 6). With this material combination, the specific mechanical, structural, thermal and acoustic properties can be improved and designed compared to the monomaterials and laminates without fibre reinforcements. However, the restricted formability of TFMLs at room temperature is a strong limitation. Therefore, the approach of this study is concerned with the fundamental description of the influence of warm forming on the degree of the forming improvement of pre-bonded TFMLs sheets experimentally via the investigation of the deep drawability and determining the forming limit curves compared to the formability of steel and MPM sheets. Two elevated test temperatures (200 and 235 °C) besides the room temperature are considered. The results of this approach revealed that warm forming could lead to over 300 % improvement of the forming limit curve (FLC) level of TFML; however, an ignorable difference between 200 and 235 °C is found. For steel and MPM sheets, increasing the temperature showed a slight improvement. Regarding deep drawing, similar results like for FLC were found, where the drawing depth of TFML could be increased from approx. 15 mm up to at least 40 mm before cracking. However, other failure types arose like wrinkling and core squeezing-out. Therefore, a one-step deep drawing approach for TFMLs is foreseen, where the adhesion and forming processes take place simultaneously.