Abstract
The engine oil pan is used for restraining pollutant and gathering greasing oil from the engine components' surface which is significant for thermal dissipation and preventing deterioration of oil quality. The study intended to investigate and develop a hybrid sheet hydroforming process for fabricating an innovative high-capacity oil pan that has the characters of asymmetrical cavity depth and major lateral bulging. Firstly, a two-stage hydromechanical deep drawing (HMDD) process was accomplished, which included precedingly regional and eventually integral deep drawing assisted by fluid counter force. The finite element modeling (FEM) was employed to study the impact of the die fillet dimension as well as the loading routes on the formability of the preformed part. The limited drawing ratio can be enhanced from 2.34 to 2.77 for AISI 304 by HMDD. Hydro-bulging was subsequently investigated by the simulations accompanied by the relatively experimental verification. Both the simulated and experimental results showed that there is a remarkable influence of lubrication condition and intermediate heat treatment on the formability of the final part. The cracks occurred at the corners of the main bulging area can be alleviated by reduction of friction coefficient. Furthermore, wrinkles and cracks have been completely eliminated and the thinning ratio can be reduced to 31.8% for the final part, when intermediate heat treatment is additionally employed. It was concluded that the present hybrid sheet hydroforming process is feasible and sufficient to manufacture a sound engine oil pan without any defects through the optimization of the process parameters.