Application of Hydroforming Technology for Exhaust Manifolds

The method of applying fluid pressure to form sheet metals as well as pipes into desirable shapes has been applied in the automotive industry [1], and it is generally referred to as hydroforming technology. Typical examples include hydroformed engine cradles and I.P. beams made from pipes. In the case of hydroforming a pipe, the applied internal pressure is often extremely high in order to expand the parent material to the desirable profile. Subsequently, an enormous amount of clamping force is required to hold the pipe in the die cavity. Various means have been developed to balance the internal force generated by the fluid and the external forces required to hold the pipe in place. Employment of a press is often the solution utilized to overcome the internal force in order to cope with higher internal hydraulic pressure. However, this paper focuses on a uniquely-designed machine which effectively handle the extreme pressure required and the reduction of the multiple set-up for parts with complex geometry. Manufacturing processes between the conventional and hydroforming methods are reviewed and compared. A set of exhaust manifolds have been developed, for a current 3.8 liter production engine, in conjunction with this hydroforming method.