An experimental and theoretical study on constitutive model of Al-2024T4 for sheet metal incremental forming

Incremental sheet metal forming (ISF) is well known as a die less and flexible forming method and is widely used for prototype part fabrication. It can extremely improve the forming limit of sheet metal. But how to get the stress-strain curve of material with improved strain limit to be used for analysis of incremental forming process? Comparing with classic global forming method, sheet metal incremental forming is local forming method. It means that any time only a small zone of entire component is deforming and moving correspondingly with the forming tool head and is undergoing a complex loading history during the forming process. Based on these characteristics, in the present study, a constitutive model is proposed to describe the stress-strain curve of material and to research the mechanism of high forming limit phenomena in ISF experimentally and theoretically. Three aspects are focused on: firstly, a constitutive model is proposed to describe the stress-strain curve of material and to adapt to the complex loading history and to analysis the mechanism of high forming limit. Secondly, an incremental forming paradigm with truncated conical shape is conducted with geometrical relationship between tool and sheet metal to calculate the strain path of sheet metal around the tool head. Thirdly, the mechanical properties are gained by tension test before and after truncated conical component made by incremental forming. The forming limit diagram is obtained by measuring and calculating the grids printed on the surface of truncate conical component. The calculation algorithm with the proposed constitutive model is programmed to calculate the plastic forming strain and stress of truncated conical component during incremental forming process. The proposed constitutive model is compared with experimental results and can be used to analysis forming limit of incremental sheet metal forming.