Hybrid self-pierce riveting is being used to an increasing extent for car body production. The combination of rivets and adhesive improves the stiffness and crash safety of vehicle bodies. However, there are a number of challenges to be met, including air inclusions and adhesive leakage from the riveting points. Atlas Copco has developed a smart solution with a new application pattern.
A combination of self-pierce rivets and high-strength structural adhesives ensures high energy absorption in the event of a collision and also provides protection against corrosion. However, the high force required for riveting often results in adhesive leaking out between the material layers or quilting between two riveting points. This causes undesirable material accumulations and air inclusions, which not only affect the overall appearance of the joint but also result in wasted material, increase the corrosion risk and can weaken the entire joint.
Perfectly balanced Material Distribution
“At our Innovation Center in Bretten, we have developed an innovative application pattern that solves these problems and significantly improves the quality of hybrid joining processes,” says Christian Messenbrink, hybrid joining specialist with Atlas Copco IAS. The material is applied in a wavy or zigzag pattern. This characteristic shape prevents air inclusions because the air can escape between the individual zigzags when the parts are pressed together. Thanks to variable frequency, application is highly flexible and the distribution of the material can be precisely controlled. At the riveting points, a lower application frequency, with wider waves, is used and less material is applied. This means that no excess material is squeezed out when the rivet is inserted. In contrast, a high application frequency, with more tightly spaced waves, is used to apply more material between the rivets. When the parts are pressed together, the adhesive is distributed evenly, with the optimum layer thickness.
With a zigzag application pattern, the adhesive material distribution can be optimized at the rivet points and inbetween. This avoids quilting and squeeze-out.
Higher Quality despite reduced Material Quantity
Comprehensive tests at our Innovation Centerss have produced astonishing results. Compared with conventional bead application with a diameter of 2 mm, the zigzag application pattern reduces adhesive requirements by more than 15 percent. The pressed adhesive pattern scarcely has any air inclusions and ensures 20 percent more effective coverage of the surface with adhesive. Adhesive accumulations and quilting are significantly reduced. All these factors contribute to joints with durably high quality. “The first material tests and customer trials are already in progress and we are working flat out to develop an applicator that is ready for production,” says Messenbrink.
15 % Material Saving
20 % more effective Coverage of Surface with Adhesive
75 % fewer Material Accumulations