~ 2008 FFC Technical Paper Excellence Award Winner ~ This study involves the work hardening of the bending operation on hydroformed parts. Generally, hydroformed parts having the complicated shape of the automobile require a three-dimensional bending operation. This operation involves several variations in the tube, including thickness, mechanical characteristics, hardness, circumference, and so on. The effect of the variations on the hydroforming operation and hydroformed parts is studied. We used two methods, computer simulation and an actual test in the plant. We analyzed the results of two experiments with several tables and graphs.