Modeling of the heating sequences of lightweight bimaterial billets for hot forging

Lightweight products can be designed to have lightweight core that is fully enclosed in a steel shell. 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 and also contributes to the load carrying capacity to some extent. The bimaterial product is conceptualized to be hot forged from a bimaterial billet, which is a steel tube press fit with a lightweight 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 is selected because of its availability as a tube.

Induction heating was selected as the heating method for bimetal forging (steel plus aluminum).  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.  Models also will be conducted with other lightweight materials showing other opportunities for the technology.