Adhesives are not a new response to challenging technical issues, as a glance at the history of aircraft manufacture shows. Even the very first aircraft were made from wood and textile components that were glued together. The Fokker F-27 represents another milestone, having gone into service featuring a safely bonded aluminium structure over sixty years ago.
The principle behind adhesives is always the same: an adhesive that sticks strongly to itself (cohesion) as well as to the surface of the components to be bonded (adhesion) is inserted between two or more components. The range of technical adhesives, for an extremely variable range of applications, continues to grow. Adhesives’ suitability for the production process and quality standards, as well as their mechanical and thermal qualities, aging, solubility, and resistance differ accordingly. For instance, depending on their application, adhesives may harden within a fraction of a second when heat or light is applied, or may take several days to do so. One challenge is the way in which adhesives age, as this can affect the solidity of bonds over time. The development of safe, secure processes and the ability to monitor the bond make it possible to develop adhesives for use even in circumstances where the solidity of the bond is safety critical.
Elimination of geometric design constraints as a result of the production process has increased the range of solutions for engineers to choose from. You can read more about how new manufacturing processes are making it possible to optimise components for load and weight in our entry on the 3D printing revolution. The vast potential of these processes is not solely derived from the layered construction that enables novel honeycomb structures; there is also a lot to be gained from the massively reduced period between the production of the first digital model and the physical article. Moreover, modern composite materials such as fibre-reinforced plastics are an essential element of this process of innovation, and you can read more about the role played by alternative materials in the future of the aviation sector in our article on high-tech fibres.
However, although materials and technologies to process them are frequently already available, there is still one aspect that inhibits mass production: the need to optimise bonding. While new materials and components may be optimally designed to meet their individual requirements, they also need to be combined to create the finished product. The core criteria of bonding technology have not changed: the cost, duration and durability of the bond must be kept in balance. Traditional joining processes such as screws, rivets and welds are reaching their limits, as they combine poorly with new materials and forming processes. For instance, the holes that are required for rivets and screws inherently create local weaknesses in the metal. When welding is used, hybrid joints represent a significant problem. In addition, localised heat can have an unwanted effect on material properties, giving another reason why engineers and scientists are seeking alternatives.
Happily, the research has paid off. Adhesives are now an essential part of automotive manufacturing, as demonstrated by the fact that each new car contains between 15kg and 18kg of adhesives. In the future, this proportion could rise significantly again. Not only are adhesives are increasingly used for structural joints, replacing conventional processes as a result, but there are other areas where there have always been few alternatives to the use of adhesives. This applies to electronics in particular, where displays, control units, sensors and electric motors are automatically bonded into place.
The benefits of adhesive bonding include the rapid bonding speed that can be achieved, increased structural rigidity, and the potential to save both costs and weight. These result not only in cost savings by reducing the use of fasteners such as rivets and screws, but also from the ability to integrate multiple functions at once. Indeed, adhesives can not only hold components together; it can also serve as a damper for vibrations, act as an electrical conductor or insulator, or absorb deformation energy. Adhesive connections ensure a high level of fatigue resistance and a uniform distribution of stresses, counteracting metal fatigue on components. This means that adhesives are ideally suited for applications in the automotive and aircraft-building industries.
The automotive industry is increasingly relying on hybrid bonding to join body parts together. This involves a combination of adhesive and bonding by forming (known as clinching). The adhesive is first applied to the individual components, before they are bonded together by forming, resulting in a particularly reliable bond. This high degree of fixation is primarily required in a crash scenario, as components can only absorb the immense forces if the bonds hold together. Accordingly, bonded bodywork performs better in crash tests than welded components. What is new, however, is that the integration of hybrid bonding into the production process introduces efficiencies in its own right as the mechanical aspects of the bonding process provide initial strength while the adhesive hardens. The result is a high level of fatigue resistance without affecting the production time.
In the aviation industry, adhesives had primarily been used to attach panels to sandwich structures in the interior and for on-board electronics. In addition, however, adhesives are used to provide stiffening and to dampen vibration in engine components. However, as emissions reductions become necessary for passenger aircraft, the potential for lightweight construction afforded by adhesive bonds becomes increasingly attractive. The automotive industry has already led the way in this respect, and more and more structural joins are now engineered via adhesives in the aviation industry as well. As a result, the scope for developments in the design of the aircraft – particularly in the fuselage, wings and tail – has expanded significantly. This design flexibility will also be needed to meet the aviation needs of the future, as shown by the promising designs for flying wings show. Read why the flying wing could be the shape of things to come in our perspectives for upcoming developments in aviation.
Bonding technology is experiencing developments that are more exciting than any have been for a long time. While traditional processes such as welding and riveting appear to be stagnating, adhesives offer new possibilities. Once again, it is high-tech industries such as the automotive and aircraft industries that are at the cutting edge in introducing new technologies and deploying adhesives in highly demanding structural applications.
Application engineers in the fields of vibration damping and adhesive technologies, surface technicians, technical assemblers, laminators, and vehicle bodywork technicians have a competitive edge as a result of their specialist knowledge. At ARTS, you can use this capital to support our customers as they turn their visions into reality. Work with us to effect this exciting transformation and create the products of the future – so start by using our job board to apply for your dream job!