In this study, upset forging experiments were performed on various uneven boundary frictional conditions generated using combinations of dies and specimens with differing surface conditions. Experimental points were established based on the experimental results as a regression using the response surface methodology and three-level full-factorial design of experiments. A regression model was constructed from a second-order model with interactive components by adopting a pointer variable and different qualitative parameters. Furthermore, a general regression model involving both frictional isotropy and anisotropy was constructed to predict the plastic deformation of materials after upset forging. The validity of the general regression model for the deformation of a forged piece was examined by conducting a finite-element analysis using the DEFORM-3D software. The simulation results demonstrate the reliability of the model in predicting the inhomogeneous friction pattern from the observed agreement between the finite-element analysis and experimental results.