Stiebel Eltron uses DS Automotion AGV for flexible Heat Pump Assembly

Stiebel Eltron GmbH & Co. KG is a globally leading heat pump manufacturer based in Holzminden, Germany. Established in 1924, the manufacturer of electrical implements, room heaters and water heaters is among the pioneers of this technology, commencing heat pump development and production during the oil crisis in the nineteen-seventies. Since then, the general increase in consciousness for the environment and the climate change fueled a rising demand. Long before the recent geopolitical distortions accelerated this trend with a steep increase of gas prices, Stiebel Eltron decided to expand its production capacity at its Holzminden factory,

The 2,000 employees in the heat pump competence center there produce numerous air source, ground source or water source models in various performance categories for outdoor and indoor use. This wide product variety and demand fluctuations took the model-specific assembly line to their limits, where the unfinished heat pumps were moved between work stations on pushcarts. This concept proved less than flexible.

As all manual tasks until compressor placement can be performed in equal work cycles, the first two manual workstations within Multiline are linked with a pusher chain conveyor. The work cycles of the subsequent step where the refrigerant circuits are soldered are considerably longer and vary from model to model. This is why a driverless transport system with automated guided vehicles (AGV) takes care of the transport to these four stations.

The same applies to the subsequent transport to where the evaporators are added, to the test chamber and finally to a buffer storage. From there, AGVs haul the heat pumps to a transfer point, where a conveyor system takes over and transports them to the manual work stations where cabling, insulation and housing are added.

The Stiebel Eltron streamliners already had years of experience with driverless transport systems, so they did not have difficulties adopting this technology for their concept. The “Streamlining and Equipment” department also acted as the prime contractor in the implementation of the Multiline installation with its variety of technologies.

For the rigid conveyor systems, Stiebel Eltron awarded the contract to Knoll Maschinenbau GmbH. This company also supplied the carrying fixtures that can be adapted using plastic receptacle inlays made by Stiebel Eltron to support all sizes of heat pumps. These fixtures are used on the rigid conveyors as well as the AGVs.

The OSCAR undercarriage AGV can navigate in confined spaces. Due to the servo motors of its proven drive technology, it boasts smooth running and high positioning accuracy even in particularly narrow stations. The vehicles maintain their course with free navigation using contour-based (SLAM) localization. At the Stiebel Eltron plant, this is supplemented by dead reckoning using magnets embedded in the ground at regular intervals to further improve precision. Thanks to their extremely low build with only 310 mm shoulder height, the AGV is suitable for a wide variety of undercarriage transport tasks.

“Within the Stiebel Eltron Multiline, OSCAR omni not only carry the heat pumps on the carrying fixtures between the manual work stations”, states Kai Hoffmann, Sales Manager Germany with DS AUTOMOTION. “They also supply the soldering stations with the required material in trolleys.” With an integrated 160 mm lift, they can automatically pick up and set down loads up to 1,000 kg. “Driverless transport using OSCAR omni allowed us to reduce the area required for the buffer storage by 50 percent”, Roman Flegel stresses. “This also keeps distances and trip times short so we only need four vehicles.”

The NAVIOS fleet manager software calculates the driving tasks for the AGVs, using data it receives from the ERP system as well as the conveyor system. With this, it communicates using the open UPC UA protocol, among other things to coordinate the load transfer. NAVIOS also administers the buffer storage. Its functionalities range far beyond those of fleet management itself.

Not only at the Stiebel Eltron plant but in all recent and future installations, NAVIOS uses the standardized VDA 5050 interface to communicate with AGVs. “This provides users with the freedom to use third-party vehicles as well, if these are better suited for the specific transport task at hand”, Kai Hoffmann explains, and Roman Flegel adds: “Even though we currently do not see no reason for this, it is comforting to know we have the option in case of need.”

Although due to the high order level, production had to continue in parallel, Multiline was built and commenced production in less than a year. “The line has been working in a three-shift operation since it was commissioned in mid-2021. In addition to faster reactions, it also gives us the opportunity to produce new product types or pilot series there”, says Roman Flegel. “Linking product and order information with the intelligent, AGV-based transport solution, with our partners, particularly with DS AUTOMOTION, we jointly created a digitalization and Industry 4.0 showcase.”

As it frequently happens in projects based on the latest technologies with this complexity and numerous interfaces, the start was not frictionless. “DS AUTOMOTION did not let us alone with this and were always immediately at hand for problem-solving or modifications”, Roman Flegel confirms. “After some ‘teething troubles’ were treated, Multiline has been brilliantly fulfilling all our expectations, ensuring long-term efficient and economic heat pump production.” Most importantly, it facilitated the envisaged increase in production capacity, allowing Stiebel Eltron to double the output on the same floor space.