Page 27 - MetalForming June 2011

duction. It operates a press line com- prising a Schuler 500-ton hydraulic preform press and an 8500-ton hydro- forming press. The line is tended by five high-payload robots—model KR150 robots from Kuka Robotics Corp., Clinton Township, MI. The robots are particularly well-suited for transfer and load/unload tasks, allow- ing Schuler to support the design and manufacture of prototypes as well as high-volume production.
Discovery of Carbon-Fiber End Effectors
Prior to 2005, all of the robots’ end- of-arm tooling used at Schuler for part handling was constructed by outside suppliers. This approach proved cost- ly and still resulted in some reconfigu- ration and tuning at die tryout, accord- ing to Schuler plant manager Craig Zeleji. The firm then decided to try its hand at building end-effector tooling inhouse. It developed a design based on readily available, interchangeable com- ponents using standard 2.5-in.-dia. tubular aluminum for the main boom. Extension arms, designed to hold clamps and magnetic grippers, were fabricated from 1-in.-dia. aluminum tube.
While attending an industry trade- show in 2006, Zeleji spied an alternative tooling solution: carbon-fiber tooling (from German supplier Bilsing Auto-
mation, also in Clinton Township, MI). The tooling was designed to replace traditional aluminum products. What piqued Zeleji’s interest was the poten- tial benefits associated with tooling constructed from high-modulus, light- weight graphite carbon fiber.
Zeleji set out to evaluate the car- bon-fiber tooling on a Chrysler pro- duction-hydroformed component for an engine cradle, weighing about 20 lb. At the time, the baseline tooling being used in production at Schuler was constructed of aluminum, with a rotation device mounted on the leading edge of the end effector. The tool han- dled two blanks—it picked and placed one blank for cleaning and lubrication, and placed a second blank, following lubrication, into the die cavity.
A Heavy Load
Schuler designed the process with a two-cavity die, although the robot could only load one component at a time due to the combined weight of the parts and the end effector. The weight of the tooling limited robot effi- ciency and made tool changes cum- bersome. Further, the weld joint at the end-effector pivot point became sus- ceptible to cracks.
Says Zeleji: “The challenge was to more efficiently manufacture these types of parts, since we were running at below rated press capacity for stroke
rate, because the robot could only han- dle one part at a time.”
Carbon-fiber tooling addressed these problems by providing a lighter, stiffer alternative. Because robot per- formance depends on the weight (and weight distribution) being cantilevered, the use of carbon-fiber material leads to increased speeds and quicker set- tling times within the working envelope of the robots, promising throughput gains.
The Carbon-Fiber Value Proposition
When Zeleji began working with Bilsing, Schuler already had designed the tooling for a complete solution, from the part back to the robot’s wrist. Conforming to standard interchange- able sizes, Bilsing’s carbon fiber was relatively simple to integrate into the end effectors.
Says Zeleji: “Since the carbon fiber is interchangeable with the aluminum, it was used as a direct replacement. This allowed us to immediately begin ramping up for production.”
Use of carbon fiber not only allowed the engineers to manufacture tooling in the same diameters, but it offered sig- nificant strength and stiffness advan- tages over aluminum. To achieve the same strength of carbon fiber, Schuler would have had to double the wall thickness of the aluminum tubing—
Common Misconceptions
Work remains in order to convince more metalformers to con- sider use of carbon-fiber tooling, according to Ben Pauzus, gen- eral manager of Bilsing Automation North America. “We can dis- pel some of the common myths associated with carbon fiber if companies would take a look at the benefits to be gained,” says Pauzus. “Although carbon-fiber tubing is more expensive than aluminum, in the overall scheme of production tooling, the end- of-arm framework comprises just a fraction of the overall cost when you include the pricetag for the grippers, magnets, clamps, etc. Therefore, the premium paid for the carbon-fiber framework is easily offset by its light weight and stiffness, and the potential gains in productivity.”
Generally speaking, carbon-fiber components weigh half (or less) than do comparable aluminum parts. Carbon-fiber tools also exhibit good toughness and wear resistance, and can be used in applications where high heat and hot flash are issues. Contrary to popular belief, today’s high-modulus carbon fiber offers increased strength and rigidity without being brittle. This
makes the material easy to manipulate and simple to integrate into tooling.
How does this benefit press-tending applications? Consider, for example, a recent Bilsing customer that had designed a large steel end effector required to carry a 2700-lb. load. The frame itself weighed more than 615 lb. Altogether, the weight of the part, end effector and tooling exceeded the capacity of the robot. A redesign of the end effector using carbon fiber reduced the weight of the end effector by 500 lb., resulting in a 114-lb. tool and bringing the total weight within the robot’s capacity limitations.
Additionally, carbon fiber can help to extend the service life of robots simply due to the harmonics. Carbon fiber absorbs vibration rather than transferring it to the robot, where it wears on joints and other components. Carbon-fiber tools also cease to bounce or shake almost immediately after settling into position, reducing or eliminating the need for clamping devices used to prevent bounce and shake associated with aluminum end effectors.
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