A high-pressure hydraulic system as described in U.S. Pat. No. 6,493,913 for hydroshaping a hollow workpiece has a lower die and an upper die vertically shiftable above the lower die between a lower position engaging the lower die and forming therewith a cavity shaped to hold the workpiece and an upper position spaced above the lower die. A hydraulic cylinder is braced between the upper die and a press actuator that can shift this cylinder and the upper die from its upper position to its lower position. A fluid line is connected between the cylinder and the interior of the workpiece and serves for internally pressurizing the workpiece.
Thus with this system the hollow workpiece is typically fitted to the lower die, its ends are plugged if it is a tube, and it is connected via the pressure line to the upper-die cylinder. The press actuator is then operated to shift down the cylinder and, with it, the upper die until this upper die abuts the lower die, at which time the cylinder is compressed so that pressure increases in it and in the workpiece until the workpiece bulges outward to fit the cavity of the die. Connecting the cylinder and workpiece together with a pressure line ensures that pressure in the workpiece will not rise to dangerous levels until the dies are solidly closed together, and uses a single mechanical actuator to both close the die assembly and pressurize the workpiece.
With this system, a hydraulic locking press is required that as far as its control system is concerned, is designed such that during the hydroshaping process the die assembly is closed for a certain period. The holding time for example for chassis parts such as side members and cross bridges is in the range of 5 to 10 seconds. This results in cycle times in the range of 30 to 40 seconds for producing a finished workpiece including transporting the workpiece to be shaped toward the die assembly as well as transporting the shaped workpiece out of the die assembly.
The pressurizing/control system for the press is provided with electronic and hydraulic pressure controllers, valves, hydraulic pumps, hydraulic cylinders and sensors. Due to the plurality of electrical and hydraulic workpieces, the system is too slow for hydroshaping along with mechanical presses as far as series production is concerned. Additional manufacturing operations on the workpieces, such as punching, stamping or cutting are carried out an additional manufacturing process after the hydroshaping process.