Hydroformed vehicle frame assembly and method

A method of forming a vehicle frame module including a pair of side rail structures interconnected by a cross structure, comprising:

• (i) forming each of said pair of side-rail structures by:
• forming a conical tubular metal blank, said conical tubular metal blank having a wider end portion an a narrower end portion;
• joining said wider end portion of said conical tubular metal blank to one end portion of said cylindrical tubular metal blank by welding to form a welded tubular assembly;
• hydroforming said welded tubular assembly by placing said welded tubular assembly into a hydroforming die cavity and pressuring an interior of said welded tubular assembly with hydroforming fluid so as to expand said welded tubular assembly into general conformity with surfaces defining said die cavity, said die cavity surfaces defining a generally octagonal shape along a portion thereof so as to conform said conical tubular metal blank portion of said welded tubular assembly therewith and thereby provide said conical tubular metal blank portion of said welded tubular assembly with a generally octagonal cross-sectional configuration;
• (ii) forming a pair of connecting sleeves, each formed separately from said side rail structures, said connecting sleeves having a relatively narrowed end and a relatively wider end;
• (iii) disposing said connecting sleeves in surrounding relation to respective ones of said side rail structures in the vicinity of said welded joints of said hydroformed welded tubular assemblies;
• (iv) welding said relatively narrow ends of said connecting sleeves to said respective ones of said side rail structures;
• (v) attaching opposite ends of a cross member to said connecting sleeves so that said cross member extends between said connecting sleeves.