Estimation of incremental sheet forming force is required in order to design dedicated equipment, utilize adapted machinery or develop online process control strategies. In the present work, forces on Single Point Incremental Forming (SPIF) of variable wall angle geometry were studied under different bending conditions. The effect of several process parameters was analyzed. The results demonstrated that the maximum forming force increases with the tool diameter and the step down while for higher spindle speeds the forming force decreases. The last effect is due to the higher friction between the tool and the blank when using a fixed spindle speed, which causes an increase of the forming temperature. The forming force evolution, which varies with the bending conditions, could be used as an indicator to prevent the sheet failure