Recently, a concept to produce lightweight products by hot forging a steel shell that had a lightweight core was presented that could lead to component weight savings up to 50%. Some targeted products are gears, valves, and flanges. The steel shell is envisioned to carry most of the load in a target application while the lightweight core serves as a space holder during the forming process. After forming, the lightweight material may either remain in the component and contribute to the load carrying capacity, or be emptied out to achieve the ultimate weight reduction. In this paper, the concept studied is hot forged from a bimetal billet, which is a steel tube press fit with a solid aluminum core and welded shut with steel end caps. For the experimental part of the studies Al 7075 was selected as the core material due to its high strength to weight ratio and 1020 steel was selected because of its availability as a tube. Induction heating was selected as the heating method for bimetal forging. This is due to the ability of induction heating to rapidly heat the steel layer. Successful bimetal forging of a closed vessel requires the steel layer to be in the austenite phase prior to the aluminum reaching high temperatures to prevent compromising the weld seams. Modeling of the induction heating process is complex due to the dimensional movement of components during the process. A method was developed to accurately model the induction heating process and predict power requirements. The method will be described and the results of the models will be compared to experimental findings. The forming process will be discussed in another paper at the conference. The simulation presented is for solid state forging of a steel aluminum billet, but the method for modeling the process is the same for hot hydroforging or other material combinations.
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