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Reliable Mass Production of Brake Light Switches

Stäubli Robotics

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 maximisation of output and reliability of process. A pioneering plant with a highly productive injection moulding machine and two ultra-precise robots as key components is taking care of those jobs where cycle time is critical.

When a car manufacturer nowadays relies on just one provider for the mass production of a component, that amounts to both an honour 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, an installation by automation expert M.A.i. GmbH has been handling this job. An injection moulding machine is at the heart of the cell. Four contact pins per brake light switch are moulded 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, ultra-precise Scara performs this task with aplomb. Eight trips are necessary to completely fill the buffer with a total of 32 contacts.

While the Scara places contact pins in the buffer, the big six-axis robot serves the injection moulding machine.

Masterpiece of automation
This buffer is situated within the working range of the large Stäubli six-axis robot. From here, the RX160 picks up the 32 contact pins and embarks on a cycle that has been optimised down to the last detail. The programme allows precisely 5.7 seconds for the loading and unloading of the injection moulding machine.

To reliably comply with this cycle time specification, the Stäubli RX160 must fulfil a complex set of requirements. Jochen Ley, moulding specialist at BCS summarises: “The robot must be very fast whilst sacrificing nothing in terms of accuracy. We are working to tolerances of a few hundredths of a millimetre 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 centres 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 moulding 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.”
About Stäubli: Textile Machinery, Connectors and Robotics
Stäubli is a mechatronics solution provider with three dedicated divisions: textile machinery, connectors and robotics. With a workforce of 4000, Stäubli has a presence in 25 countries and agents in 50 countries around the world.
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