Research on Gentle Loosening of Solidified Bolted Joints for Complex Capital Goods

Abstract

The consideration of sustainability is increasingly becoming a focus in research and production. For example, the recycling process for products that are no longer usable should be optimally prepared by separating materials by type as far as possible. In addition, products should be made usable again by repair or replacement if only sub-components fail. In the case of complex capital goods, like aircraft engines, it is mandatory to preserve the product since damage to the joining partners can lead to immense costs. A decisive factor in this context are assembly connections, which have a major influence on the complexity of disassembly. Concerning this matter, detachable connections, like screwed joints, have many advantages for service, repair and recycling compared with permanent fixing solutions. They can reduce assembly time, simplify maintenance processes, and greatly reduce maintenance time and costs. However, during a product's life cycle, threaded connections can corrode, leading to damage or even failure of the bolted joints. Beyond that, they can solidify and often only be disassembled destructively. In this article, we present an approach to improve the loosening of operational solidified screwed connections. It is well known that vibrations during operation can reduce the preload force of the connections. We exploit this aspect by inducing vibrations through micro impacts to alleviate the loosening torque of the solidified bolted connection. Depending on the direction of the vibration (torsional or axial), that can ensure a gentle and component-friendly disassembly to a greater or lesser extent in contrast to destroying the screw by drilling or shearing and splitting with the risk of damaging the product being maintained. The designed experimental setup with a piezo actuator allows us to investigate the amplitude and frequency of the induced vibrations for the required disassembly force. The results show that our approach enables component-conserving disassembly, as the forces can be significantly reduced.