Screw fastening 100 percent secure screw head support

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In screw connections, the goal is to achieve optimal and homogeneous head support. Numerous influencing factors complicate this optimum, and existing torque-controlled industrial screwdrivers are reaching their limits. The Aixtight inspection system could be the solution here.

When components are optimally connected with screws, numerous influencing factors must be taken into account. Screws, drilled holes, and the components themselves are subject to certain tolerances. There are also various surfaces and material pairings. The currently used torque-controlled industrial screwdrivers can only inadequately consider these different conditions. The result is poorly fastened components with loose screw connections. The engineering firm Aixtrusion from Arnsberg has developed an inspection system called Aixtight, which can detect faulty screw connections directly during assembly and thus eliminate them before delivery.

"A long-standing customer from the automotive sector approached us and reported problems with the screwing of control units with a plastic housing," recalls Thomas Frerich, Business Development Manager at Aixtrusion. The customer's example specifically involved direct screwing with self-tapping screws of a force-feedback control unit. "With the modern screwing systems used, it repeatedly occurred that screws did not reach the head seating consistently. As an engineering firm with over 40 years of industrial experience, our developer heart was immediately on fire, and we took on the challenge," Frerich proudly recounts. This was the birth of Aixtight.

The goal: A homogeneous and optimal head support

But why is such a measurement system needed? "When screwing components, various influencing factors must be considered. In addition to material-based properties, dimensions of fastening holes and screws, as well as the condition of the surfaces, play a major role," Frerich explains. Each influencing factor is subject to a certain tolerance range. This becomes particularly complex in direct screwing of plastics but also of aluminum. "Additionally, with the use of these materials, the torques often have to be chosen to be lower, and screws can't be tightened up to just before the yield point, as is common in the gradient method," the expert describes the problem.

Achieving a homogeneous and optimal head seat is of paramount importance, especially for components made from these materials. The focus is always on achieving the required clamping force. "This ensures that the components are securely connected and that any introduced system forces are adequately absorbed," says Frerich. The quality of the head seat can also determine whether a screw connection is liquid-tight or not. This is relevant, for example, in the screwing of batteries as used in electric vehicles.

Infrared measuring method ensures optimal screw head support

But how does the Aixtight measurement method work? When screwing in a screw, friction occurs when the screw head contacts the component. "This friction generates heat, which we can detect with the infrared camera of our measurement system. Our software analyzes this measurement in real-time and reliably determines whether the screw head has seated or not," Frerich describes the system. Environmental temperatures from the production environment or the heat generated by the tapping process during screwing do not affect the measurement. The thermal image thus obtained is compared with reference data and provides direct insight into the quality of the screw connection. Precise positioning of the screw head ensures that the specified preload force is achieved and an optimal connection is made. This allows each screwing carried out with Aixtight to be evaluated directly during assembly. The user immediately sees on the HMI whether the screw connection was OK (IO) or not OK (NIO). "It is also possible to pass this information to a quality system for documentation. Concerning integration at the customer's site, there are no limitations," the expert explains the possibilities.

Easily integrable into existing screw systems

Aixtight is a standalone measurement system that can be easily mounted on an existing screwdriver. "Thus, an existing, manufacturer-independent screwing system can be simply expanded with this smart detection," says Frerich. Even more: With infrared detection and evaluation via the software, it succeeds in closing the gap where torque/angle-based screwing processes and previous head seat detection systems stop.

But it goes even further. Together with a leading manufacturer of sensors and systems for force measurement, Aixtrusion was able to demonstrate that their infrared detection linearly correlates with the shutdown preload force of the force sensors. "Thus, it is now possible to indirectly prove the achieved preload force of the just-performed screwing based on our infrared measurement. A unique advantage for any quality assurance, especially in series production, as until now, the preload force could only be verified sporadically in the lab with special experimental setups," reveals the expert.

Since mid-2024, the measurement system has been available with standard software. Initial installations have been made. The feedback from the industry has been consistently positive. "We encounter great interest, especially in the automotive industry. Of course, there was some skepticism, but we are more than willing to present our system and test it with customer components." The approach here is "First Test Before Invest."