These days implementing lightweight materials is an overriding consideration in vehicle construction, but car manufacturers still are on the lookout for methods to improve stiffness, increase crash durability and reduce metal/material fatigue, all the while contributing to weight reduction.
Among all safety-related manufacturing applications in the automotive industry, structural bonding is the most important. Structural-bonding seams perform strength-relevant functions on the body frame where structural adhesives complement spot welding and reduce its use. Since the entrance of extremely high-strength epoxy-based adhesives into the market, structural-bonding seams have increasingly replaced spot welding. Because fixing is necessary until the adhesive has cured, welding is still used.
Structural-bonding is the ideal application field for the stitch bead method. Because adhesive would normally be burned during through-welding, its application is interrupted exactly at the locations where through-welding takes place. The high application speeds required by the process make a very fast application unit an absolute necessity. Application units should also be designed to offer a long service life and to deal with the near constant, high stress levels to which they are exposed.
Atlas Copco IAS has been very successful in applications for bonding the outside and inside sheets in the hem flange areas of doors, hoods and tailgates. Using our proprietary E-Swirl technology, it is possible to improve the distribution of adhesive in the flange areas of components.
The main advantage is that the adhesive can enter the remaining grooves more easily when the sheets are joined and ensure optimum filling. If the cavities were not properly filled, air could be trapped in small pockets during the subsequent sealing operation. This air, in turn, could escape during the hardening process, thereby spoiling the appearance and effectiveness of the sealing in resisting corrosion. If too much adhesive is applied in these areas, cost intensive retouching is required.
Anti-Flutter / Gap-Filler
The function of an anti-flutter application is to reduce or eliminate any "fluttering" or vibration of the outer and inner panels relative to each other. This application is more commonly used on horizontal closure panels such as hoods and deck lids ̶ and to a lesser degree on vertical panels, like doors and lift gates.
The shape of the applied adhesive is also very different. Instead of a bead, the adhesive is applied in the shape of a gumdrop or chocolate drop. It is strategically spaced across the inside surface of the outer panel, aligning with the shape of the inner panel.
The placement also provides support for the outer panel to pass compression tests. It's developed to withstand loads, such as the weight of someone sitting on the hood without causing a dent.