Nothing Sits Idle

When it comes to investing huge sums in automation, manufacturers worldwide share a common wish list. They want equipment that delivers high throughput, produces quality parts, and takes up as little space as possible.

Germany's Schuler AG, a long-time pioneer in metal-forming innovations, is fulfilling those wishes. The company's new crossbar transfer press eliminates idle stations between presses and prevents defects in complex auto parts. It wins the Design News/Omron Global Innovation Award.

Those results have already prompted orders for eight of the presses in Europe and the U.S. No small accomplishment, considering that each press costs about 35 million Euros.

"This machine is going to stir a lot of interest," says Louis Kren, a senior editor who follows press technology for MetalForming magazine. "Schuler is one of a handful of companies that leads the pack in large-scale automation."

No More Idle Stations

The most important innovation in the new press, says Hans Hofele, director of Schuler's Automotive Business Unit, is its decentralized transfer system. Unlike previous crossbar transfer presses, which relied on a centralized mechanical drive, the new system features autonomous transfer units with their own electronic drives.

"These modular transfer units are independent and fully programmable," explains Hofele. "They also can be tested at Schuler facilities prior to installation, which makes start-up of the whole system much faster."

In this new design, two drives positioned opposite each other in the press frame connect to a carbon-fiber crossbar via swing arms. Together, the drives form the transfer unit between two press stages. Additional drives built into the swing arms allow for seven axes of motion, allowing the transfer unit to rotate, reorient, or separate parts on the fly between two stations.

The design allows manufacturers to program the transfer motion for two forming stations at a time, according to the particular part shape. Independent drives also allow operators to adjust press speed and transfer motion separately, so that even difficult shapes with inclined forming positions in the die can be produced in a continuous operation.

"With older presses, you had to design the stamping operation to handle the most complicated part," explains Uwe Kreth, Schuler's head of product management. "You couldn't modify the press to run faster for less complex parts."

The new design also eliminates the need to devote costly factory space to idle or universal stations between press stages, where parts must wait for further processing. That amounts to about a 15 percent space savings overall. Instead, the modular transfer units pick up a part with vacuum cups from one forming station—and in one swinging motion place it directly onto the next press.

"Eliminating the idle station is the wave of the future for large transfer presses," says Paul Kosaian, director of Ford's North America Stamping Operations, who adds that the new Schuler design will cut the length of the press line by about 20 ft. "We also expect an increase in up time, because we aren't handling the part as much, which reduces the chance for error and damage."

The entire Schuler compact crossbar transfer press consists of five forming stations—also called "slides"—that extend about 25m. A typical installation also includes an area in the front of the press where steel sheets or "blanks" are taken from a destacker, then washed, and recoiled. The first of six transfer modules then picks up each blank from a conveyor and inserts it into the first station—the draw stage—which gives the blank a 3D shape. Dies in successive stations perform additional punching, cutting, and trimming functions. Finally, the last of the modular transfer units takes the finished part from the final forming stage and places it on a turntable that feeds into two exit conveyors.

Kreth, the head of product management, explains that the new press is much more flexible than conventional transfer presses and can produce a wider array of parts. Designed to handle large auto parts, such as trunks, hoods, and entire side panels, the press can operate at a maximum rate of 16 strokes a minute. Depending on the size of the part, the system can produce from one to four parts per stroke. Overall, Kreth says the press delivers at least a 10 percent increase in output versus conventional cross bar presses.

Simplicity and Quality

Flexibility and space savings aren't the only benefits. Jeff Grube, manager of the Press Group for Bosch Rexroth Industrial Hydraulics in Bethlehem, PA, cites the simplicity of the new design as a major reason for its success. "Instead of having five mechanical drives for each of the five presses, you have only one large drive, situated on the crown of the press," Grube explains. "This reduces the number of components and makes for higher reliability."

Simplicity also marks the design of another key innovation in the new transfer press: its "hydraulic bed cushion," which controls the forces within the dies and prevents damage to the part as the upper die moves down against the stationary lower die. Together with Bosch Rexroth in Germany, Schuler developed this new modular cushion with far fewer components than earlier designs. Located in the pit or "basement area" below each station in the press, the cushion's programmable cylinders perform several functions, such as damping, pre-acceleration to adapt the cushion to the speed of the press, and an upstroke to aid in part removal. Either a Bosch's MX-4 or a Beckhoff controller drives the actuators for the cushion.

"This cushion system is really what makes this press so much better than anything else on the market," says Bernard Kristen, VP of Engineering for Morrell Inc., a distributor and engineering services firm in Auburn Hills, MI. "You have much finer bend radiuses on auto parts today, and the cushion system prevents fatigue cracks and other defects."

Working together with Schuler and with components from Bosch Rexroth, Morrell is building the power units that provide the cushioning, lubrication, and hydraulics for the new Schuler presses now being installed at Ford and GM plants in the U.S.

In the coming months, Ford will operate the presses at plants in Louisville and Buffalo, while GM will install the presses at four plants in Michigan, Ohio, and Indiana, according to Hofele, the Automotive Business Unit manager.

Proving the Concept

Those new U.S. orders for the new compact crossbar transfer press follow seven years of development work for Schuler, whose distinguished history includes the world's first transfer press in 1900 and the first mechanical crossbar press in 1990. Before Ford installed the first of the new compact presses in its Saarlouis, Germany, plant in September 2003, Schuler had already tested the system with over 2 million strokes—equivalent to a year's operation—at Schuler headquarters in Göppingen, Germany. Throughout this testing process, Schuler refined the design, in part as a result of suggestions from its automotive customers.

"It would be a very high risk to bring such an expensive new technology to market without trying to make it perfect," recalls Hofele.