We obtain an equation for estimation of the instant of the loss of contact between a die and an obstacle. We study the impact in the framework of the plane dynamic problem. It is assumed that the length of the die exceeds its transversal dimensions considerably. The contact loss is caused by the superposition of waves reflected from the side surface. We present a relationship between the instant of the loss of contact, on the one hand, and the ratio of the shear and the volume velocities of the waves, on the other hand.