In Cleveland, OH, is a forging press owned by the Air Force and operated by Alcoa to make high strength structural components from lightweight alloys for commercial and military aircraft. With a forging capacity of 50,000 tons, it is one of the largest fabricating tools in the world and is now a historic landmark. In 1974, the press was refurbished and a new control system installed. The new system allows the fabrication of large pieces of titanium and aluminum metal alloys with fewer fasteners and less machining.

50,000 ton press

In 1981, this press was one of two of its size and the largest in the Western World. Larger view.

The unique control system offers a huge multiplication of the efforts of its operator, as well as hairline precision. The press, which weighs 11,000 tons, responds instantly and precisely to the lone operator’s hand on a lever just 3” long. His slightest touch governs 2100 tons of moving weights, and can exert up to the full 50,000 tons of force.

Personnel of the Rexnord Hydraulic Products Division designed and manufactured the massive hydraulic system. Vital statistics on the system are staggering. There are 23 major control valves, some of them weighing as much as 12 tons with, operating at 4,500 psi. Fluid flows range from 11,750 gpm at high pressure to 26,438 gpm at prefill pressure.

Eight main cylinders, all 60” in diameter, deliver the press’s working force by advancing the press platen. Four check valves, weighing about 12 tons each and standing 9’ tall, prefill these main cylinders to bring the platen quickly into contact with the workpiece. Four pullback cylinders move the platen back through the return portion of its cycle. The majority of the control valves are driven by a single camshaft 30’ long which synchronizes them through a series of rocker arms.

Two closed-loop electronic-hydraulic servo systems work simultaneously as the press operates. The main system is operator controlled, positioning the main camshaft, which in turn actuates most of the system’s operating valves via a positive linkage. A signal is transmitted from the 3” control lever, through electricly controled hydraulic servo control circuitry, resulting in positive mechanical positioning of all control valves, affecting a corresponding and proportionate speed and position of the forging platen of tke press. Closed-loop feedback circuits maintain a precise response equal to the movement of the operator’s control lever.

valves and cams for press control system

Massive valves and large camshaft are needed to withstand the forces involved. Larger view.

The secondary system is a unique tilt control system. This compensates instantly for out-of-level conditions occuring during the power stroke caused by irregularly shaped forgings. The eccentric loads this creates can cause high stresses in portions of the press structure, weakening it and leading to premature failure unless the loads are counteracted imediately.

The digital analog leveling system uses four encoders to monitor and compare instantly the four corner positioning of the moving platen. Actual position of the platen is shown on a video display screen at the operator’s station. In the case of the tilt control system, these signals are also fed through a servo mechanism to two balancing valves, each controlled by a servo-controlled hydraulic cylinder, to make necessary corrections automatically by directing high pressure fluid to the proper main cylinders so as to maintain the level of the platen.