Measuring System Error-Free Forming Processes Through Real-Time 3D Measurement Technology

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In the DIKUQ project, researchers at Fraunhofer IOF have developed a partially automated process chain for forming sheet steel for shipbuilding. A new type of inline 3D measuring system digitally captures workpieces in less than half a second and reconstructs them as a 3D image.

When bending steel sheets weighing several tons for the hull of a ship, the final geometry often depends on the trained eye and experience of the worker. Millimeters decide on accuracy of fit and stability. Until now, skilled workers have repeatedly stopped the production process to manually check for shape deviations - a time-consuming and error-prone process. However, conventional approaches to digitalizing these processes from industrial series production can hardly be transferred to the individual production of single pieces in shipbuilding, which is precisely where the joint project DIKUQ ("Digitalization of cold plastic forming through continuous quality control"), funded by the Federal Ministry for Economic Affairs and Energy (BMWE), comes in: In the project, the Fraunhofer Institute for Applied Optics and Precision Engineering IOF and partners have developed a partially automated process chain for the cold plastic forming of ship components. The project partners are Ostseestaal GmbH & Co. KG, which is also the project coordinator, the Fraunhofer Institute for Large Structures in Production Engineering IGP, the University of Rostock and MSR-Service GmbH. One focus of the project is the precise, digital recording of workpieces along the entire process chain.

Sensor Network for 3D Reconstruction

At the heart of the project is a high-speed inline 3D measuring system: a low-latency 3D sensor network that allows for the digital capturing of the workpiece, enabling precise target-actual comparisons directly at the press. The system consists of two synchronized cameras on the right and left sides of the workpiece, which are coupled with the corresponding projectors. This allows for a measurement volume of up to 4 m x 2 m x 0.5 m (16 ft x 7 ft x 1.6 ft)to be fully captured in less than half a second. The captured image sequences are reconstructed into a precise 3D model of the workpiece using triangulation.
 The core of the system is a surface-based 3D measuring method using structured light in the near-infrared range (NIR). "An irregular pattern is projected onto the object's surface, which deforms according to the geometry of the workpiece," explains Dr. Christoph Munkelt, a scientist in the Imaging and Sensing Department at Fraunhofer IOF. "The distortion of the pattern then provides us with the information needed for the 3D reconstruction."

Digital Test Template Compares Process Data

"The decisive advantage over conventional methods lies in the real-time feedback," the IOF researcher continues. "The system creates an automated target/actual comparison with the target geometry, which is projected onto the sheet metal. This allows the worker to see immediately where reworking is still required in order to achieve the target corridor." Physical inspection templates, which used to be time-consuming to set up and evaluate, are no longer necessary. Instead, a digital "inspection template" is available, which can be compared with the process data at any time.

Our goal is to digitally support the forming process, which has primarily been shaped by the expertise of the workers.

The system's precise, digital feedback makes it possible for new employees to learn complex work steps that were previously anchored exclusively in the experience of the workers. "Our aim is to provide digital support for the forming process, which has so far been shaped primarily by the know-how of the workers. In doing so, we are countering the shortage of skilled workers, increasing process reliability and making jobs more attractive," explains Maximilian Müller, Head of Research and Development at Ostseestaal.
By digitally recording the workpiece geometry, quality fluctuations are minimized, higher fitting accuracy is achieved and the return rate is reduced. At the same time, the system creates seamless, traceable documentation of quality control for the end customer. The automation concept can also be transferred to industries with similar requirements, such as aerospace and architecture.