Process analysis and investigation of defects in multistage cold forging by using finite element method

F.Bassan
Zoppelletto

Much progress in forging technology including low production cost and fast production has allowed an intensive use of forging. Manufacturing companies have especially focused on producing a complex shaped part with a tight dimensional tolerance. Traditional warm and cold forging methods have their own limitations to produce such a complex shaped part; warm forging requires complex system with relatively higher manufacturing cost, while cold forging is not applicable to materials with limited formability. Therefore, multistage forging may be advantageous to produce complex shaped parts. Multi-station forging machines with automatic work transfer between stations permit very high production rates to be reached, but considerable time and effort by skilled personnel must be spent in workplanning and their setting up and timing.
In recent years numerical simulation has been used in the forming industry and has become essential in most companies. The traditional time-consuming and costly trial and error method has been replaced by more and more sophisticated simulation software that can now address the whole manufacturing process. At the same time, the dramatic improvement in hardware power as well as the development of always more efficient algorithms has made it possible to simulate the most complex parts within very short computations times. Modelling and simulation of manufacturing process chains are important for decreasing the defects induced by the manufacturing processes and increasing the life of the components during production. The precision of cold forging parts becomes critical because the process depends on many factors such as the size and complexity of the parts. Defects negatively affect the assembly accuracy and the performance of the parts. Therefore, defects must be detected and prevented as soon as possible before the manufacturing process begins.
In the present paper, a process sequence for multi-stage cold forging is designed with the rigid-plastic finite element method to form an heating pipe fitting. The numerical model, carried out by using the code Forge®, includes investigation of velocity distributions, effective strain distributions and forging loads, which are useful information in process design and defects prediction. The FE results are compared with those obtained with the real process and a very good agreement is observed.