2. Experiment
2.1. Experimental method
In Fig. 1, the developed equipment is shown. With this equipment, it is possible to measure friction coefficients
under the high pressure and long sliding distances which occur when forging steel. A billet was backward extruded
with the rotating punch at a very slow rotational velocity. The rotational velocity was determined not to influence
material flow. Through the backward extrusion, the punch rotated only 6º. Load cells were installed below the
container to measure torque and load for calculating friction coefficients. On the contacting surface between the
bottom of the billet and the container, grid patterned snags were made to suppress slippage. The punch and
container can be heated up to 623 K (350 ºC) with the heaters. The equipment was placed in a servo press
(3000kN). A hydraulic die cushion (500 kN), placed below the equipment was used to knock-out the billet after
testing.