The rear lift gate on the Audi A3 consists of three sheet metal panels, each with a different thickness, joined with round clinch joints. To cut down on cycle times, Audi AG (Ingolstadt, Germany) installed a robot from Kuka Robotics Corp. (Clinton Township, MI) and a robotic clinching unit from TOX-Pressotechnik (Warrenville, IL). Audi also wanted a system that would be flexible and reliable, even when faced with large production runs.

The force to form the individual joints is supplied using a TOX electromechanical servo drive. Seven 6-millimeter round joints attach the stiffener element to the gate's inner panel. Each month, the system installs approximately 100,000 round joints with highly reproducible and documented quality.

The process requires 21 kilonewtons of press force, with a 2,000-newton stripper force for the punch side and a 625-newton stripper force for the die side. A special SKB-type die with moving and fixed segments forms the joints. The cycle time is 1.8 seconds.

The quality control dimension for the round joint is 0.3 millimeter. This dimension represents the remaining bottom thickness measured inside the resulting joint cavity and is dependent on the type and thickness of the sheet metal layers. To guarantee a quick cycle time, the die is moved at high speed during approach and retraction. It slows down just before contacting the workpiece.

The electromechanical servo drive makes it possible to join panels with different thicknesses using just one robotic gun. The result has been savings in both equipment and maintenance costs. Changeovers have been eliminated. During setup, each joint location and its parameters can be easily programmed and controlled.

Since installing the system, Audi has had the robot and clinch gun in production 24 hours a day for 10 months without any downtime.

The servo drive is also considerably lighter than the standard drives used in robotic guns, and the gun's envelope has been reduced by approximately 30 percent. In both cases, the result is increased robot performance.

For more on robotic clinching, call 630-393-0300, visit www.tox-us.com or eInquiry 1.

For more information on robotic assembly, call 586-569-2082, visit www.kuka.com or eInquiry 2.