Precision under steam
Since it was founded in 1973 with just 18 employees at the time, the German manufacturer, RATIONAL GmbH, from Landsberg has become the world market leader in steam cooking appliances for commercial large-scale kitchens.
Together with its 31 subsidiaries worldwide, the listed manufacturer of large-scale kitchen technology now employs more than 2,200 people, with trained chefs alone accounting for a quarter of the workforce.
The fully automated production sequence at a glance: The FD-V210 handling robot from OTC DAIHEN EUROPE, clearly visible in the foreground, loads the laser welding cells and removes the corresponding parts from the upstream component containers.
Like many other companies of its size, RATIONAL was keen to simplify production processes in order to adequately and cost-effectively meet the ever-increasing demand. In the course of the production of cooking chamber parts in Landsberg am Lech in Germany, and Wittenheim in France, the welding process had already been automatized; supplementary handling tasks such as loading the welding cells were still carried out manually - a bottleneck in the production process that needed to be optimized.
In 2017, the go-ahead was given for full automation of the entire handling and welding process for cooking chamber interior boxes for RATIONAL steam ovens. LASOtech Systems GmbH, based in Suhl, Thuringia, was entrusted with the implementation of this ambitious project. Founded in 2007, the special machine builder specializes in engineering and production of customized solutions in automation technology, as well as special machines. The company has extensive expertise in the integration of existing production facilities or production lines, right through to turnkey-new systems in the automotive and non-automotive sectors. In addition to automated grinding processes, as well as the classic joining techniques of screwing, riveting and gluing, laser and MSG welding processes in particular are part of the Thuringian company's repertoire - another circumstance which qualified LASOtech to carry out this project.
Eventually, the components intended for the cooking chamber were to be welded exclusively by laser and without filler materials. Due to the highest optical as well as hygienic requirements, this welding process has no alternative for the thin stainless steel sheets used here. Plasma and TIG welding processes, on the other hand, generate significantly more heat, which would unnecessarily deform the sheets.
The two FD-V210 OTC handling robots used moved independently of each other on a 15-meter long, robust chassis made of polymer concrete and were responsible for various handling tasks.
During the planning and implementation phase, the clamping, welding and handling technology were automated. Due to the complexity of the required motion sequences and the high coordination effort between the handling and joining tasks, LASOtech and RATIONAL had to work closely together until all sub-processes finally meshed seamlessly.
After about nine months of project planning, the first equipment for pre-production could be set up in 2018. Since the beginning of 2020, production has been running in three-shift operation. In the end, the plant for the automated production process was built a total of four times in almost identical design: three of them for automated welding of a smaller cooking chamber inner box for a steamer with more compact dimensions, the fourth plant specifically for significantly larger inner boxes. Each of these facilities is about 25 meters long and 15 meters deep and requires only one operator. The production of the inner boxes varies in height depending on the intended number of slide-in units; the footprint remains the same for three plants, while the fourth is significantly larger.
"In each of our plants, two FD-V210 handling robots from OTC DAIHEN EUROPE operate on a 15 m long, vibration-resistant chassis, which is made of polymer concrete, without a classic steel foundation. The system core is formed by four laser welding cells, which are supplied with parts via eight container stations”, explains Gernot Hofmann, project manager at LASOtech Systems GmbH. The robots feed the various clamping and welding processes with the corresponding parts from the respective component containers and move them continuously from station to station until all joining tasks are ultimately completed. Parallel processes take place continuously here. While the shielded laser welding processes are taking place in the laser booths, stations are being loaded elsewhere - a complex process organization. In the past, the individual components were laboriously welded manually. Today, welding in the stations is automated via portals by means of laser optics. The weld seams produced in this way meet RATIONAL's requirements to perfection.
An overall plant and sequence control system (PLC) coordinates the portal and robot axes to ensure optimum plant synchronization. The created PLC program ensures a coordinated and automated process flow in the systems. In addition, the RMU (Robot Monitoring Unit) of the Japanese robot manufacturer ensures that the positioning of the robots in relation to each other and with regard to all safety requirements is met. In this way, no robot can intervene in a placement cell when the door is open, unless this is provided for in the production sequence. Since the thin components have some instability, one hundred percent repeatability in the placement of the stations is essential.
Insight into the fourth laser welding cell: Here, the FD-V166 robot from OTC DAIHEN EUROPE with laser optics, which can be seen in the background of the picture, ensures highly precise welding results.
"In addition to the coordination and positioning software, the FD-V166 robot from OTC, used for the laser processes, is particularly noteworthy. Unlike many comparable robots in this weight class, it is capable of welding a 0.5 mm wide circumferential weld with a diameter of 30 or 150 mm, with high precision - while using the process-related gas cover to prevent oxidation of the components during welding. The solid mechanics installed here, with gears that are robust at the same time, give the OTC robots the necessary stability and rigidity in combination with the controllers that are optimally suited for welding tasks: "Even for such precision tasks in a weight class where other robots often cannot keep up in direct comparison", explains Frank Neuenhaus, system house supervisor at OTC DAIHEN EUROPE.
LASOtech was able to fully apply the advantages of robot technology from OTC DAIHEN EUROPE to this complex construction project. This production automation expert from Thuringia, which has implemented numerous projects, has not only been a sales partner of the Japanese group for several years, but has also been part of the DAIHEN Corporation since 2019. The synergy effects between the globally active DAIHEN Group and the experienced system integrator have since enabled LASOtech to increasingly serve international customers. It is a merger that, taking into consideration the ongoing shortage of skilled workers and the industry's continuing trend towards laser processing technology, is beneficial for both sides: the intelligent combination of robots and peripheral equipment in the context of system integration, as well as the design of fully automated production lines, will continue to be the key disciplines for increasing the track record of innovative companies.