The Mega Cell

The assembly of pressure relief valves for the ventilation of car engine crankcases is a detailed process that presents multiple challenges: an annual output of three million units, tolerances in the hundredth of a millimeter range and strict quality assurance procedures call for a superior automation solution.

Working on behalf of global automotive supplier ElringKlinger AG, the Langer-Group in Illmensee (Baden-Württemberg) operates a high-volume production line for pressure relief valves. The valves consist of two components; an injection-molded plastic part, which the Langer Group manufactures at its own premises on an Engel Victory 50 injection molding machine. This was specially purchased for this major order, along with a separately sourced membrane made of fluoroelastomer, this element has excellent resistance to high temperatures and contact with fuel or lubricants. The complete unit is installed in a vehicle rocker cover where it ensures ventilation of the crankcase and the harmless release of fumes and oil vapors.

For the task of combining the two components into the finished item, a fully automated solution was needed that could guarantee reliable around-the-clock production. Markus Beierl, Head of Injection Molding at the Langer Group, explains: “We produce about three million of these valves annually, so there is no room for delivery delays or quality fluctuations.”

The specifications in terms of precision for this process demanding. The components are small and delicate and the fluoroelastomer membranes has a diameter of just five millimeters. These must be inserted in the injection-molded part within a tolerance of a few hundredths of a millimeter. Assembly by hand was ruled out primarily on the basis of accuracy specifications, although it would not have been an option anyway in view of the production volume.

Robotics essential for the planned level of output

Markus Beierl and his team decided at the very start of the project that robots would play a key role. They would have to be fast and precise, as well as reliable and low-maintenance: “At a trade fair, we saw a demo application that convinced us of the benefits of the Stäubli SCARA range - and after extensive research into all performance data, we selected Stäubli as our robot supplier.” Soon afterwards, the specifications were written up and an expert partner for the design and the assembly plant was found in SFA, a manufacturer of special machinery based in Aichstetten, Baden-Württemberg.

In May 2018, the innovative assembly plant went into operation. The key components in the cell are two Stäubli TS40 SCARAs. The highly dynamic and precise four-axis machines manage all handling and assembly steps within the cell, which is also equipped with a rotary indexing table. Two Asyril Asycube 240 feeder systems deliver two components; the injection-molded casing and the membrane. A stationary image processing system located above the feed tray supplies positional data to the first of the two TS40s. This enables it to pick up an injection-molded part and correctly position it in the work piece holder on the turntable.

The turntable then rotates to the first of the two integrated QA stations. Here an image processing system validates the injection-molded part conforms to size and has been correctly deburred.  Any part that found to be faulty is passed through without being processed and sent to an enclosed chute.

Error rate in the parts-per-million range

More than 99.9 percent of the parts proceed to Station 3 where the membrane is attached; this can be a complicated process. The second Stäubli SCARA selects a membrane from an Asycube 240 platform and inserts it into the injection-molded part; the SFA developed a special suction contour gripper for this, which has such precision that it achieves an error rate close to zero. “At this key station, the exceptional performance of the Stäubli TS40 makes a decisive contribution to the success of the entire assembly cell,” says Beierl. “The four-axis machine assembles the finished item with unprecedented dynamics and precision while fulfilling rigorous cycle time criteria.”

After it has been put together, the valve passes through another QA station, where a vacuum/overpressure test takes place to ensure that it functions correctly. Once completed,  the rotary table returns the part to the station where the process began. The infeed robot will also handle the removal of the finished and tested parts.

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. With its high-grade equipment and the two Stäubli robots, this enables the plant to operate with hardly any interruptions and therefore continuous high-volume production can be relied upon.