In this study, the production process of eccentric head bolts that fasten flanges for water supply pipe connections, which can only be achieved through the cold forging process, was improved. For axial forging, forming analysis was performed for a 200-ton header machine to check the raw material specifications, forming load, and metal flow improvements suitable for forming. The analysis found that the forging of high-strength bolts of M14×65 ㎜ with eccentric heads was possible under the maximum load condition of 137.2 tons with low carbon boron steel of ø13.8×89.7 ㎜ and 105.2 g. By mounting the prototype mold on the header machine, it was possible to prevent metal flow breakage, as shown by the trial mass production test. It was possible to improve the strength of the eccentric head bolt and reduce the weight of the input material through the cutting process. Therefore, manufacturing costs could be reduced.

Process and die design of cold forging for the asymmetric part, engine mount adapter has been studied. Forging of the asymmetric part frequently causes die failure because of the high forging load and local stress concentration of the die. Thus, performing process design of cold forging to minimize forging load is required. Preform for the engine mount adapter was chosen based on the forging load and filling rate of forgings by the finite element analysis. In the die design, number of stress rings, interface radius, and relative interference were investigated in several cases with maximum principle stress by the finite element method. The shape of the die was determined by comparing the load changing the radius of the flange area. Also, the life of the designed die was calculated using the Goodman theory by cyclic fatigue loading. As a result, it was confirmed that the calculation life and results of the test were identical. In this study, it is verified that stress concentration and fatigue life should be considered simultaneously in the design of cold forging die for the asymmetric part.