Universal Alloy Corp. (UAC), a business unit of Alu Menziken Aerospace Group, Reinach, Switzerland, and manufacturer aluminum alloys, recently purchased and upgraded the world's largest indirect extrusion press to expand its aerospace market offerings. Built in Germany in the 1940s, the 122-foot extrusion press originally made aircraft components in World War 2. The press, which now extrudes 16,200 tons, was disassembled, shipped, and reassembled at UAC's Canton, Ga. facility — where it began production in early 2005 after an extensive revamp effort.

A Part of History

Originally, the 14,000-ton water-hydraulic horizontal three-stage extrusion press was used mainly to extrude magnesium and aluminum aircraft components. One of the stories UAC has heard is that this press made aluminum skins for V-1 rockets, but the company officials don't know for certain if that ever happened.

After WW2, the press was shipped from Germany to the U.S., as part of a U.S. Air Force heavy press program. The press was acquired by Dow Chemical Corp. and reassembled in Madison, Ill., where it was used to extrude magnesium alloys mainly for aircraft and missiles. Its third owner was Spectrulite Consortium, St. Louis, which used the press to produce aluminum and magnesium extrusions. In 2003, UAC purchased the press rights from Spectrulite with the goal of expanding its aerospace business. In addition to the new press, the UAC facility in Canton operates four extrusion presses ranging from 900 to 2750 tons.

Hydraulic Overhaul

In direct extrusion, a heated tool container that encloses a billet (the raw piece of metal used for rolling into bars, rods and sections) is fixed in relation to a die during the extrude cycle. Approximately 50% of press tonnage is lost, due to a backflow condition that occurs in the tool container. In indirect extrusion, the tool container moves along with the press, over the die. With this process, only 20% of tonnage is lost to container friction, resulting in higher cycle speeds. However, press speeds (in tonnage) increase four times with indirect extrusion. This challenges the hydraulic designer on a big press to have accurate flow controls at both ends of the spectrum.

The Bosch Rexroth Hydraulics Systems and Engineering Group, in Bethlehem, Pa. provided the hydraulics package for the press, as well as the direct and indirect shears and two stretchers. The package included five hydraulic systems, piping and field startup assistance. The hydraulic systems consist of:

  • 17,000-gal main reservoir,
  • 1000-gal water/glycol reservoir,
  • 60-gal unit run-out saw reservoir,
  • 850-gal, 1500 ton stretcher reservoir, and
  • 1200-gal, 350 ton stretcher reservoir.

Paul Scaglione, UAC vice president of engineering, explained that the hydraulics conversion was important to meet requirements for the next 20 years. "There were unique challenges in the conversion," said Scaglione. "We had to build the 'Swiss Army Knife' that could run direct extrusions, indirect extrusions, and seamless hollows. We also had to be concerned with the large amount of hydraulic operation above and around the heated tooling at the front platen."

The tooling is heated to 800° F, including the heated container that weighs 50 tons — a large mass operating above the flash point for conventional hydraulic oil. The original water press fluid was fireproof, as is the water-glycol now used.

Big hydraulics

Jim Lane and Otto Weber, systems engineers for Bosch Rexroth, worked closely with UAC to design multiple hydraulic systems for the massive press. The package included a huge 17,000-gal hydraulic system — featuring a reservoir, pilot system, motor pump groups, and manifolds.

Each of two prefill tanks is a 12,000-gal air-over-oil low pressure accumulator. Prefill tanks flow up to 7600 gpm and are charged to approximately 60 psi. Four main pumps have an output of up to 600 gpm at 4500 psi, while a container strip pump can achieve 8000 psi.

The extrusion rams advance 4.7 in./sec, and return at 4.5 in./sec. The main ram has an impressive 65-in. bore and 13.4-ft stroke. Two lateral rams have 48-in bores and 13.4-ft strokes, while two return rams feature 16-in. bores and the same stroke.

The four main pumps, which operate the extrusion cylinders, are Bosch Rexroth variable displacement servo-controlled pumps. Each has a design flow of 150 gpm. The system includes both closed-loop speed and pressure control.

The system also uses a Bosch Rexroth proportional directional control valve to control fast advance velocity, as well as acceleration and deceleration of the press. (Only minor velocity adjustments are made once extrusion starts.) The valve is used as a meter-out flow control when the press fast advances, using the pressurized prefill tanks. Flow exiting the return rams during fast advance is about 520 gpm.

A complete complement of logic valve technology is used for system fluid management. Variable displacement pumps and/or proportional valves reduce shock when the press accelerates or decelerates and also control velocity. Logic valves provide directional control and safety interlocks on circuits with large flows. Bosch Rexroth logic valves are rated for operation at up to 14,500 psi. The valves control the stripping function of the press, up to 8000 psi.

Handling the billet and die

According to Lane, billet and die handling on the press is aided by a 1000-gal water/glycol hydraulic system that operates at 4500 psi on the hot side of the press.

First, a die slide moves heavy dies into the press. A lock then secures the die in the press, and lift cylinders lift a butt catcher into position. (A butt is the unextruded portion of the billet remaining in the container after the extrusion cycle is completed.) A butt eject cylinder pushes the butt into the butt catcher, and swivel cylinders move the butt catcher into and out of the press. Direct and indirect shears (also hydraulically operated) are used to cut the extruded part from the butt. Hydraulics also operate the die slide, which is used to load dies for different shapes into the press.