Experimental and numerical investigation of fiber metal laminate forming behavior using a variable blank holder force

Abstract

Structural integrity, fuel efficiency, and reduced emission of greenhouse gases are the topmost priorities of the modern-day aerospace and automobile industries. Fiber-metal laminates (FMLs) can reduce most of these concerns by reducing a significant amount of weight without compromising structural reliability. Although this material was invented a few decades ago, large scale production, especially the forming process of small and complex-shaped products, has not matured yet. The necessity of manual processing makes it more cost-intensive and time-consuming. The forming difficulty comes with the limited elongation of the fiber layers compared to the metallic layers. As a result, the conventional approaches to form FMLs parts are not very suitable. In this paper, an investigation has been conducted to improve the drawability of FMLs sheets in deep drawing of cylindrical cups, made of semi-cured Glare material. A variable blank holder force (VBHF) method was proposed, which means the variation of the friction force of the holder and the laminate on contact surfaces, as a function of the position of outer flange edge. Fracture and wrinkling limits have been determined, and a BHF control trajectory has been presented to improve the forming quality, increase the drawing depth, and eliminate defects. Both experimental and numerical results from the VBHF were compared with constant BHF results. It is evident that the proposed VBHF scheme helps to improve the drawing quality compared to the conventional constant BHF. As a result, this method can enhance the production rate as well.