Ultrasonic vibration Ultrasonic energy is applied to a die in an ultrasonic vibration-assisted metal forming process, and the die is used to deform the workpiece. The friction between die and workpiece decreases when ultrasonic vibration is applied in metal forming process. The friction plays a crucial role in metal forming; therefore, the friction force must be evaluated and quantified to obtain the optimal forming process. The ring compression test is widely used to evaluate the friction factor or coefficient of friction. However, the ring compression test is unsuitable to determine the friction condition in forging and extrusion processes. Therefore, this study evaluated the effect of ultrasonic vibration on the friction factor using double cup extrusion tests (DCET). The apparatus design for ultrasonic vibration-assisted DCET and experiments were conducted, and the commercial finite element software Marc was used to simulate the DECT to obtain the friction calibration curves. The results demonstrated that the evaluation of the interface friction factor using DCET is sensitive. Under no lubricant condition, the friction factors of traditional and ultrasonic vibration-assisted DCET were approximately 0.1 and 0.3, respectively. Under Blue Moly lubricant condition, the friction factors of traditional and ultrasonic vibration-assisted DCET were approximately 0.05 and 0.1, respectively.