One of the authors previously proposed a new forging method of using flexible rocking motion. This method reduced the load by nearly 50%, compared with method without the rocking motion. The effects of rocking type and blank holding condition on forgeability were studied in this work. Holding one end of the specimen prevented the specimen from slipping during rocking-die forging under a well-lubricated condition. By reducing the rocking angle and increasing the rocking frequency, forging load was decreased and the flatness of the end of the specimen was improved for every rocking type. Finite element analysis was carried out under the same conditions as the experiments. The numerical results qualitatively corresponded to the experimental results. It was suggested that the rocking motion decreased the contact area, aiding the reduction of load.

We have proposed a new friction test method under severe friction conditions. The method applies backward extrusion, which enables us to create high surface pressure, large surface area expansion and a long sliding distance. In addition, die temperature in the actual forging processes can be reproduced. The unique feature of the die set used in this method is a punch rotating at a very slow angular velocity. From the combination of measured load P and torque M, friction coefficients μ of the entire punch contact surface can be calculated. The equation between M/P and μ was derived using FEM analysis. This equation depends on the punch shape, not the flow stress of material. By this method, we measured friction coefficients at 900 ℃-1200 ℃, in which warm and hot forging conditions of steel were reproduced. As a result, we were able to quantitatively evaluate the lubricant combustion temperature, billet antioxidant coating, lubricant spray pressure, and billet initial temperature, which strongly affect friction coefficients.