Assembly of pressure relief valves
The assembly of pressure relief valves for the ventilation of car engine crankcases is an intricate process that poses multiple challenges. An annual output of three million units, tolerances in the hundredth of a millimeter range and rigorous quality assurance procedures, call for a superior automation solution.
Working on behalf of global automotive supplier ElringKlinger AG, the Langer Group produces pressure relief valves for the ventilation of vehicle crankcases. The valves consist of two components, an injection-molded plastic part and a membrane made of fluoroelastomer. For the task of combining the two components, a fully automated solution was needed that would guarantee reliable around-the-clock production.
For this assembly plant with its output of three million parts per year, with their rigorous specifications in terms of precision, the highest standards of quality and production are required. The components are small and delicate, the fluoroelastomer membranes have a diameter of just five millimeters and must be inserted in the injection-moulded part within a tolerance of just a few hundredths of a millimeter.
High-volume production inconceivable without robotics
Since May 2018, an innovative assembly line with two Stäubli TS40 SCARAs has been producing the parts. The high-precision four-axis machines manage all handling and assembly steps within the cell which is also equipped with a rotary indexing table. The process begins with the delivery of the two components –; the injection-molded moulded casing and the membrane, – which is delivered via two feeder systems. A stationary image processing system located above the feed tray supplies positional data to the first of the two TS40s, enabling it to pick up an injection-molded molded part and correctly position it in the workpiece holder on the turntable.
The table then rotates to the first of the two integrated QA stations. Here, an image processing system checks that the injection-molded moulded part conforms to size and has been correctly deburred.
The membrane is attached at Station 3, which is quite a difficult process. The second Stäubli SCARA fetches a membrane from the feeder system and inserts it into the injection- moulded part in an extremely intricate assembly process. The TS40 has to operate with unprecedented dynamics and precision while fulfilling rigorous cycle time criteria.
Once these stages have been completed, the valve passes through another QA station, where a vacuum/overpressure test takes place. The rotary table then returns the part to the station where its journey began. The infeed robot also handles the removal of the finished and tested parts.
Error rate in the parts per million range
What the Langer Group team particularly appreciate about the assembly cell, apart from high output and impressive availability, is its outstanding autonomy. In practice, this means only one manual provisioning of parts per shift. In terms of quality, the plant boasts an impressive error rate in the parts-per-million range. With its high-grade equipment and the two Stäubli robots, the cell operates with hardly any interruption and therefore its continuous high-volume production can be relied on.