It is natural to consider that the friction coefficients are not a constant value on the entire surface of the punch.
Here is discussed the area which the measured friction coefficients represent. In Fig. 4(b), the friction coefficient
was 0.051 under the severe adhesion condition. This value is recognized as a small value. This becomes an
argument to suspect the validity of the developed method. The reason why such a small value was measured was
due to the contribution ratio of the areas of the punch on the friction coefficients. The effect of the length of the
punch land on torque is shown in Fig. 6. As shown in this figure, the contribution of the punch land on torque, and
also friction coefficients, was about 10 %. Therefore, when severe adhesion occurred at the punch land, friction
coefficients were less than 0.1.