The latches must be strong and durable, yet easy to operate. Apply too much peen, and the latch is difficult to operate. Apply too little, and the assembly is unreliable, which can adversely affect safety and customer satisfaction. Getting it just right over thousands of assemblies can be difficult.

This was the challenge faced by Interwest Services Ltd. (Red Oak, IA), a manufacturer of riveting equipment for the automotive seating industry. An electromechanical press and controller from Promess Inc. (Brighton, MI) solved the problem. The riveting head is mounted on the ram of the press, which has integrated sensors to provide real-time, closed-loop control of the riveting operation.

The key to the process is a technology known as signature analysis, in which the characteristics of a known-good pressing operation are captured and used as a benchmark for subsequent operations. By setting upper and lower tolerance limits around this signature, production of good assemblies can be ensured without the need for subsequent inspection.

The press delivers real-time torque and position information to the controller, which continuously compares that information to the signature profile of the operation. Any deviation beyond the tolerance limits will flag the assembly as a potential problem, and alert the operator to the need for remedial action. The process essentially "clones" a good operation by ensuring that all subsequent operations exhibit a similar torque and distance signature curve.

Signature analysis not only can detect potentially bad assemblies, it frequently can pinpoint the cause of an out-of-signature event. The exact shape of the signature provides important information about the individual parts being assembled. For example, rivets that are too hard or soft, or too short or long, will produce a distinct change in the signature. Similarly, a hole that is too wide or narrow will produce a different change in the signature.

Interwest’s orbital riveting station can handle a range of rivet lengths and diameters in multiple locations on an assembly. Each riveting operation is analyzed individually and compared with a torque and distance signature of that specific rivet. The result is either a certified good assembly, or a reject with an identified fault.

The controller runs both the electromechanical press with the orbital riveting operation and the X-Y motion of the pallet. This gives the user a common interface for all motion programming. The system is easily reconfigured to handle various parts by reprogramming the controller and changing the pallets that carry the fixtures.

For more information about electromechanical presses and signature analysis, call Promess Inc. at 810-229-9334 or visit http://www.promessinc.com.

For more information about automated riveting systems, call Interwest Services Ltd. at 712-623-3690.