Assembly in Action: Press System Helps Clone Limited-Slip Differentials
A case in point is the nonsynchronous automated assembly system Owen recently built for Eaton Corp. (Cleveland). The system, used to build locking differentials for light-duty trucks, uses a pressing operation in Station 5 to install two critical bushings that control the torque transfer from the slipping wheel to the traction wheel.
"The bushings have to be positioned precisely," Burtka notes. "If they’re too loose or too tight, the locking feature doesn’t work. That means an unhappy customer and a warranty claim. This is an extremely lean system. We use a number of manual presses at other stations to install various components. Eaton can vary the output of the system by using more or fewer operators as demand fluctuates."
"Don’t let the manual operations fool you, though," Burtka adds. "Every station is equipped with in-process gauging and inspection [equipment], and the final acceptance test in Station 7 is a simulation of actual on-road performance of the fully assembled unit. Every pallet has a radio frequency identification tag for process monitoring. This is a sophisticated system in spite of being lean."
However, before Owen Machine could provide the right solution for Eaton Corp., it had to find the right assembly press. Owen Machine settled on a CNC electromechanical assembly press system built by Promess Inc. (Brighton, MI). This assembly press uses signature analysis to monitor and control assembly operations with precision and consistency.
The process measures both the force and displacement of the press during a duty cycle and then relates the resulting force and distance curves to those produced by a good operation. If the curves don’t match, then the finished assemblies will have different operational properties. By setting limits for acceptable variation, out-of-tolerance products can be identified while they are being built, rather than in the field.
The press consists of an encoder-equipped servomotor driving a ballscrew ram. Various sensors can be attached as necessary. Unlike older mechanical, hydraulic and pneumatic presses, the Promess press can monitor and control both force and position, providing an opportunity to change quality assurance from a reactive to a proactive technology.
"The fact that the Promess press is a packaged system was important to us in the Eaton application," Burtka adds. "The customer only gave us 18 weeks from the time the order was placed to the start of production. To make things even more interesting, they were continuously refining the product design up to the start of the production run. We really took full advantage of the easy programming and the broad application flexibility to make the deadline. In the end, Eaton actually used the capabilities built into our system as part of its final approval for the product. I think that is taking simultaneous engineering to a new level."
For more information on assembly presses, call Promess Inc. at 810-229-9334or visit www.promessinc.com.