Precise forming and handling of large sheets

Industrial sheet metal forming requires precise and efficient handling systems in order to move large components safely. Modern solutions rely on robot-assisted systems and intelligent control systems - especially in large-scale processing, for example in shipbuilding. Despite technological advances, a holistic approach that enables an end-to-end automated process chain is still lacking.

As part of several publicly funded research projects, the Fraunhofer IGP in Rostock has developed an automated handling system for the previously manual forming process of heavy plates. It enables the precise positioning of heavy free-form plates, automated, cold-plastic forming and intelligent quality inspection throughout the entire forming process.

The crane system used, defined as a cable-guided parallel robot, combines the flexibility of a classic crane with the precision of an industrial robot. With intelligent control, sensor technology and modular expandability, it improves material flow, throughput, precision and repeat accuracy in sheet metal processing.

Handling rethought

The handling system consists of two crane bridges, each equipped with two trolleys and hoists. This allows rectangular panels to be securely attached at all four corners and handled flexibly. Each hoist has a maximum load capacity of 4,000 kg. The positioning accuracy of the entire system is in the millimeter range. The usable working area is around 400 m². The system control was implemented with a particular focus on the integration of various control algorithms for forming processes, crane operation and measurement technology as well as the connection of a database.

The control approach used, based on a soft PLC in combination with ODK technology, enables a modular, flexible structure. Despite the large number of connected modules in the network, cycle times in the range of a few milliseconds are achieved. This forms the basis for innovative, real-time capable control processes for low-vibration handling of the panels - a unique selling point of the system.

The system performs horizontal and vertical movements largely vibration-free and also allows precise rotation around the vertical axis. The basis for this is the recording of static and dynamic system parameters using position detection, inclination sensors and force transducers. The vertical plate movements are supported by optical sensors. Every point on the plate can be approached precisely. Intelligent assistance functions also support operation: an automatic calibration function aligns new plates exactly parallel to the press. Another function makes it possible to move the plate manually, with the crane dynamically following the operator's guiding movement.

The core of the system is the shipbuilding press (maximum compression force 5,000 kN) with high-precision load cells (3

×

0 to 2,000 kN measuring range) and a rotatable forming tool. The high-precision measuring technology with intelligent control detects even the smallest control deviations and corrects them immediately. The additional combination of two high-precision, optical 3D measuring systems, which continuously determine the plate geometry and provide real-time feedback for the forming process, enables the precise and flexible production of heavy plates. The measuring system offers an area coverage of the entire measuring space of more than 3

×

3 m², short measuring cycles of less than 150 ms and is also eye-safe (laser protection class 1) for the operator. These systems work hand in hand with intelligent forming planning, which always keeps an eye on the target geometry and adapts the forming strategy dynamically and in real time during the process.

Efficient quality management

An advanced, intelligent database forms the basis for communication between the crane system, operator and forming process, supporting continuous condition monitoring and ensuring efficient quality management throughout the entire process. This system is supplemented by a user-friendly visualization system that displays scanned sheet metal point clouds on an operator panel to assess the process quality. Comprehensive system monitoring and fault detection also ensure reliable production control and minimize downtimes.

This work was supported by various funding bodies as part of three research projects. Two of the projects were funded by the European Regional Development Fund (ERDF) in the Technology and Industry Initiative (TBI-V) program under the funding codes TBI-V-1-178-VBW-062 and TBI-V-1-418-VBW-142. Another project was funded by the Federal Ministry for Economic Affairs and Climate Protection (BMWK) via the Project Management Jülich (PtJ) under the funding code 03SX575D. We would like to expressly thank the above-mentioned funding institutions for their financial support and for making it possible to carry out the research work.

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Authors: Prof. Dr.-Ing. habil. Jan Sender, Prof. Dr.-Ing. Wilko Flügge, M. Sc. Christian Scharr, M. Sc. Tobias Handreg, all Fraunhofer IGP / am