Experimental and numerical evaluation of multilayer sheet forming process parameters for light weight structures using innovative methodology

Being light weight and superior in characteristics, hybrid materials such as fiber metal laminate (FMLs) and functionally graded structures (FGS) are becoming increasingly popular in aeronautical, automobile and military industries. In the present work, an innovative methodology which hereafter will be named as “3A method” has been proposed to replace complex shaped, monolithic, metallic sheet parts with hybrid parts. This method is based on simultaneous forming of any number of multiple metallic blanks in required shape by applying hydroforming (HF) technology. Based on numerical simulations, forming limit diagrams (FLDs) are established for three types of blanks forming hemispherical shaped parts using Barlat 2000 yield criteria/DYNA Form/LS Dyna. To validate the simulation results, experimental study is accomplished and optimal process parameters are determined by varying the cavity pressure under constant die-binder gap. Effects of number of layers and thickness of blanks on thinning, wrinkling and punch force have been well studied for three types of blanks and a comparative analysis is made to investigate various failure modes. To achieve a composite layered structure, post forming procedure has been devised and implemented to get a final hybrid part. Furthermore, limitations of the 3A method in terms of final shape of parts are discussed. Good agreement can be found between numerical and experimental research. The new methodology is capable of employing any types of resins and composite materials at any required place in parts for desired characteristics. Elimination of repeated heating and solidification of blank assembly as well as precise punch force and speed requirements make this multilayer blank forming method more efficient, economical and user friendly for manufacturing of FMLs and FGSs at commercial scales.