Source: Deutsche Nachrichten
The research partners were able to demonstrate that non-destructive testing methods, combined with modern data analysis, provide valuable information about the quality of sealants. This opens up new possibilities for making quality assurance in industrial manufacturing more efficient, faster, and more resource-efficient.
Sealants perform important functions in numerous industrial applications. They are used to seal joints, bond components, serve as insulators, or optimize flow characteristics. Quality assurance remains a challenge in this context: Curing behavior is often evaluated using separate samples or ensured by applying conservative safety margins to process times. Targeted defect detection is rarely performed. Inline, non-destructive testing methods have so far been available only to a limited extent. This is precisely where the “SteP-in” research project, conducted by the SKZ Plastics Center—a member of the Zuse Association—and the Fraunhofer Institute for Manufacturing Technology and Applied Materials Research (IFAM), came into play.
The project’s goal was to develop methods for assessing the condition of sealants directly on the component and during production. To this end, the research institutes investigated three promising technologies: air-coupled ultrasound for monitoring curing, optical profilometry for analyzing shrinkage processes, and active thermography for detecting defects in sealants. In addition, methods for intelligent data analysis and AI-based models for determining the degree of curing were developed.
The work conducted in the project using air-coupled ultrasound showed that changes in the intensity and transit time of the signals, as well as their derivatives, provide important information about the progress of curing. Characteristic points in the curing process, such as the so-called gel point—that is, the transition from liquid to solid material properties—could be determined reproducibly. At the same time, limitations and the need for further research regarding complex joint geometries were identified.
Noncontact, inline-capable profile measurement of sealing seams also provides important information on shrinkage behavior and the curing state. This makes it possible to shorten waiting times during curing while simultaneously improving the quality of flow-optimized seals. The measured profiles can be correlated with conventional hardness measurements to reliably determine the degree of curing using an AI model. “Compared to the contact or destructive measurement methods used to date, this is a significant improvement and an important step toward automated manufacturing systems,” says Christian Tornow, a researcher at Fraunhofer IFAM.
Active thermography also made it possible to detect surface defects, air pockets, or delaminations and, using the appropriate evaluation method, to characterize them in terms of their geometry and depth (see image). This opens up new possibilities for monitoring component quality, particularly for safety-critical applications.
“With the measurement approaches developed in the project, we were able to lay an important foundation for future inline-capable quality assurance of sealants. This enables companies to make their manufacturing processes more transparent, reduce scrap, and use resources more efficiently,” explains Daniel Hoffmann, senior scientist at SKZ. Thanks to the project’s application-oriented focus, important insights were gained for future industrial use. Numerous industries that use sealants will benefit from these results, including the automotive, aerospace, construction, electronics, and energy sectors. Currently, the research institutes are seeking companies with which to test the developed testing methods in specific applications and further optimize them.
The IGF research project with funding number 01IF23269N “SteP-in – Increasing Process Reliability in the Application of Sealants Using Inline-Capable, Non-Destructive Testing” was funded by the Federal Ministry for Economic Affairs and Energy through the DLR as part of the Program for the Promotion of Industrial Collaborative Research (IGF), based on a resolution of the German Bundestag.