Gas cylinder with time delay

Abstract

A die stamping system in which an upper die moves downwardly toward and upward away from a lower die to stamp a workpiece, and in which a portion of the lower die is supported by at least one gas cylinder coupled to gas under pressure to cushion downward movement of the lower die portion and delay upward movement of the lower die portion. Each gas cylinder has a piston reciprocable within a vertical cylinder body. The piston has an upwardly extending piston rod for engaging the lower die portion. The cylinder body has a lower portion beneath the piston connected to the gas under pressure. A first passage connects an upper portion of the cylinder body above the piston to the lower portion of the cylinder body beneath the piston. A second passage connects the lower portion of the cylinder body to a tank. A third passage connects the upper portion of the cylinder body to the tank. First, second and third valves in the respective first, second and third passages control gas flow. When the piston descends, the gas pressure in the lower portion of the cylinder body increases, and by opening the second valve this pressure is transmitted to the tank. By closing the second valve and opening the third valve, the increased gas pressure in the tank is transmitted to the upper portion of the cylinder body to hold the piston down.