Semi-hot precision forging of connecting rods

Forged steel connecting rods are characterized by a homogeneous material structure with favourable fibre orientation free of internal defects, resulting in high levels of strength and ductility. The manufacture of forged steel connecting rods is very competitive due to the economical mass production on automated forging lines and the quality of the products. Nevertheless, new challenges such as environmental demands as well as developments in other fields as for instance in material sciences require a continuous advancement of the manufacturing technology. Development efforts by various institutions and companies are aimed at improving geometrical and mass tolerances in precision forging of connecting rods. This paper presents the investigation and results of a research project on the technology of precision forging without outer flash at hot and semi-hot forming temperatures applied to a weight-reduced double-piece connecting rod. Major tasks consisted in the development of a specialized tool system, the adaptation and modification of suitable connecting rod designs with precise adjustment of preform geometry, and the optimization of forming process, technological parameters and workpiece design. In a number of test series, closely coordinated with FEM simulation, forming process and preform design have been improved in iterative steps until adequate results were obtained. The manufactured connecting rods comply with the material specifications of the automotive industry and they have been tested in fatigue tests.