forming process. The variability could be caused by minor changes in specimen thickness, property, and surface condition. During the deformation process, the instantaneous real contact area between the die and the specimen could also change and lead to variation in coefficient of friction within a test. Due to variations in many contributing factors, there was also noticeable variation in friction between the two tests with the same bending radius. The effect of normalized die radius, however, can be clearly observed. The coefficient of friction decreases as die radius increases. It is believed that the higher coefficient of friction was due to an increase in contact pressure. This is further examined in numerical simulations later.