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ROBOTIC RESOURCES

Reliable Mass Production of Brake Light Switches

Stäubli Robotics

Eight million units per year

The production of eight million brake light switches annually is subject to its own set of priorities. Flexibility is less important here than other factors such as maximization of output and reliability of process. A pioneering plant with an efficient precision injection molding machine and two ultra-precise robots at its heart is taking care of those jobs where cycle time is critical.

When a modern car manufacturer relies on just one provider for the mass production of a component, that amounts to both an honor and a responsibility for the chosen supplier. Body Control Systems (BCS), a subsidiary of worldwide automotive supplier TRW, is responsible for the production of eight million brake light switches annually for the Volkswagen Group.

Since June 2011, a plant developed by automation experts M.A.i. has been responsible for carrying out the task. An injection molding machine is at the heart of the cell. Four contact pins per brake light switch are molded using an eight-way machine tool. There are just 5.7 seconds during “tool-open time” when all loading and unloading operations have to be completed

The production process begins with the feeding of two different-sized contacts via two stamping lines. A Stäubli Scara TS60 first fetches four short and then four long contacts from the appropriate transfer station on the stamping line and passes them to a buffer store. The ultra-fast and extremely precise Scara machine copes marvelously well with this task. Eight trips are necessary to completely fill the buffer with a total of 32 contacts.

Masterpiece of automation
This buffer store is located within the working range of the large Stäubli six-axis robot. The RX160 fetches the 32 contact pins from the store and starts a cycle that is optimized down to the last detail, since the work of loading and unloading the injection molding machine must take place within a timeframe of just 5.7 seconds.
To reliably comply with this cycle time specification, the Stäubli RX160 must fulfill a complex set of requirements. Jochen Ley, molding specialist at BCS, summarizes: “The robot must be very fast whilst sacrificing nothing in terms of accuracy. We are working to tolerances of a few hundredths of a millimeter when loading the tool. The Stäubli RX160 meets our expectations in every way, with the gripper technology making a huge contribution.”

A unique feature is the use of an insertion piston to feed the tool with the total of 32 contact pins required for eight finished parts per cycle. Thanks to special indexation and a floating mounting, the robot centers exactly on the tool, making the highly accurate insertion process a reliable and fast operation. The RX160 has yet another major advantage: compact design and internal wiring. With its slender arm, it can safely reach into the injection molding machine without any external cables to get tangled up.

Jochen Ley: “Over 10,000 brake light switches leave the production cell per shift. With only two to three defective parts per 10,000 units, we are close to having zero-fault production. In addition, the plant meets all of our requirements, producing parts reliably, quickly and economically. With the large-scale production of eight million switches annually to contend with, we could not have it any other way.” 

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