Hydraulic Press Products — Shock Dampers

Have you ever been in a metal stamping facility and heard something that sounds like a train running into the building every time the press cycled? If you have, what you are hearing is an event called reverse tonnage and it is tearing up the press. In this short explanation, we will attempt to explain Reverse Tonnage also known as Snap-Through in a metal stamping press. Reverse tonnage is the undesirable results of cutting, blanking, and perforating operations. In the stamping process, the moment the punch meets the material, the press frame begins to deflect until the press has built up enough force to exceed the shear strength of the material and the punch breaks through. When this happens the press frame will release the stored-up energy and snap back past its original position or resting position into a compression load. The press frame and components that are designed to function in a tension load are now in a compression load condition and all of this will occur in less than 20 milliseconds. At the instant of breakthrough during blanking, the press and dies are subjected to severe stress. This compression load condition on the press frame is called reverse tonnage and it can damage your press. The conventional industry standard is to have presses designed to accept a reverse tonnage load that does not exceed 10% of the maximum forward capacity of the press. In other words, the maximum allowable reverse load for a 600-ton press is 60 tons. So, anything over 60 tons, you risk damaging your press.