Moving workpieces and driving innovation

Twice as many product variants with half the setup time – that's what special-purpose machine builder Harrandt has achieved with a redesign of its measuring, testing and assembly lines. The heart of the innovative new solution is a transport system based on B&R's SuperTrak long-stator linear motor technology.

"At first glance, engine pistons appear to be perfectly round and relatively indestructible," says Samy Alain Song, head of the Innovation and Electronics department at Feinwerktechnik Otto Harrandt GmbH, "but on their way through assembly, they must be handled with extreme precision and utmost care."

Taking these central requirements into account when designing piston assembly lines is becoming increasingly difficult as the pistons themselves evolve. The thickness of the rings mounted on the pistons, for example, has been reduced by half over the past decade as automakers seek to make engines more efficient. As the rings become more fragile and harder to handle, maintaining process stability during 24/7 production becomes a real challenge. "Even the slightest deviation in the assembly process can lead to quality problems," says Song.

That's why Harrandt's specialists have carefully developed and continuously refined every step in the piston assembly and testing process, from measuring the pistons with micron precision to mounting the piston rings and press-fitting the piston pins.

On a traditional assembly line, pistons are carried from station to station on conveyors driven by belts or chains. "These systems are the most cost-effective solution for high volumes, and they're very stable and reliable," Song explains. "And as long as you're running large enough batches, the relatively high number of change parts required for up to 30 piston variants and an average changeover time of around an hour and a half are of little concern. However, the cost analysis looks quite different for production runs of just a few thousand units, which are already common today." These smaller runs – caused in part by the transition to electric vehicles – call for much more flexible production options with fewer change parts and shorter changeover times.

To better serve the needs of today's users for shorter production runs, Harrandt has developed an entirely new approach to its assembly lines. The first line to be completed based on the new concept produces 2-stroke pistons. It allows users to measure, test and assemble 65 different piston variants with changeover times of only 20 to 30 minutes. Not only that, but it does so on a dramatically smaller footprint.

Harrandt's assembly line is arranged around an oval track system where the straight sections each consist of two one-meter segments. Along these straight sections, Harrandt engineers have distributed a total of ten stations.

On the two meter straight sections at the front side of the line, there are seven measuring and assembly stations. On the opposite equally-sized section of the oval rail system, the Harrandt engineers have placed a loading station and an unloading station, as well as a calibration station in between for the 12 to maximum 16 shuttles. Thanks to the new transport system, Harrandt's new lines take up only half the floorspace of their predecessors with the same number of stations and achieving the same output, as the development manager proudly reports.

"For the new generation of assembly lines, we were able to use the measuring and assembly stations from our proven high-end lines almost unchanged. On the one hand, this means that our customers can expect the same precision, stability and 7-second cycle times as achieved by the most powerful of the previous lines. On the other, it has enabled us to focus on all the new possibilities that SuperTrak offers us," adds Song.

Harrandt also retained the control system for the assembly processes, adding a B&R controller for the SuperTrak system. The control solution provides the high-speed data transmission Harrandt needs for seamless monitoring and traceability of the line's 12 (or optionally 16) shuttles. The shuttles can also be moved to any position via software with a repeatability of ±0.01 mm. As a result, pistons of different sizes can be aligned so that the casing line always comes to rest in the same place.

Harrandt has taken advantage of this positioning flexibility to develop a universal workpiece holder for cylindrical or cuboidal workpieces that can accommodate many different piston sizes. This alone has led to a significant reduction in the number of change parts and the time required for changeovers.

SuperTrak also enables higher transport speeds and slower processing steps can be distributed across multiple identical stations to maintain a faster overall cycle time. This is possible because shuttles can simply pass through unneeded stations without stopping.

If additional processing stations are needed, SuperTrak also makes it easier for Harrandt to add them. Song points out: "On the one hand, we can accommodate additional stations on the inside of the oval and perform processing in the remaining free space on the curved segments. Our internal analysis has confirmed that SuperTrak is able to meet our repeatability requirements anywhere along the track, even in the curves. On the other hand, it is relatively easy to expand the system by adding straight segments, each of which can then accommodate two or three additional stations. With a conventional line, such an expansion would only be possible at great expense and with a significant increase in footprint. Maintenance is also easier with SuperTrak. With a special tool, the shuttles can be easily removed and replaced for maintenance. Even the track segments can be easily removed and replaced, keeping maintenance downtime to a minimum.

In developing its new line, Harrandt minimized risk in several ways. First of all, there was the design flexibility gained with SuperTrak, combined with the decision to retain proven hardware and software solutions in the processing stations.

Furthermore, the ability to simulate the movements of the track system gave Harrandt's decision-makers peace of mind early in the planning phase. "The simulation gave us confidence that we were on the right track technically. It helped reduce the risk that always comes with new technology, both for us and for our customers," says Song. Harrandt also plans to use the simulation function to demonstrate feasibility and performance to customers during the bidding phase for new lines.

It's not just customers looking for efficient piston assembly lines who will benefit from Harrandt's new approach. Harrandt's new SuperTrak-based concept gives them the opportunity to apply all the process and automation know-how they have gained in the area of piston assembly to other markets.