The use of lightweight materials in auto manufacture means that traditional joining techniques are less often used in production lines and repair workshops. The materials that are bringing about this change include aluminum, magnesium, carbon fiber and other composites, as well as high-strength steel.
New ways to weld
As materials have changed, specialized welding techniques are often necessary. For example, high-strength steel may need to be tempered during the welding process. Options for welding aluminum include frictionstir welding and resistance spot welding. Using mechanical fasteners such as self-piercing rivets can be made easier by applying heat to prevent materials from cracking when they are pierced. Aluminum and steel, though dissimilar, can be welded together with friction welding as long as the thermal cycles are relatively brief. However, many of these processes extend cycle times and increase equipment maintenance needs.
Adhesives offer several advantages
1. Reduced corrosion
There are many benefits to choosing adhesives for bonding materials, not least of which the advantage of being able to prevent corrosion by eliminating direct contact between dissimilar substrates such as aluminum and steel.
2. Lightweight and high strength
As a complimentary technology, adhesives enable manufacturers to use far fewer spot welds or rivets, while helping to save weight by making strength and stiffness contributions to the materials being joined. The average new auto contains 27 pounds of adhesive, saving many times that weight in overall mass. For each meter of adhesive used, vehicle weight can be reduced by 0.6 – 1.1 kilograms. As a result, adhesives are widely used by auto makers such as General Motors and BMW.
3. Faster cycle times and reduced maintenance
The use of fewer spot welds and rivets is also important due to the specialized welding and riveting techniques that the new materials require. These add to cycle time and increase maintenance costs. Fewer welds and rivets mean that cycle time and equipment maintenance costs can be reduced.
4. Stronger bonds and a smoother, quieter ride
Because adhesives spread bonds over a wider surface area, adhesive bonds can be stronger than rivets or welds, and help increase body rigidity, which is critical to vehicle handling and performance.
Adhesives also improve driver and passenger comfort thanks to their contribution towards reducing noise, vibration and hardness (NVH).
Using adhesives in auto manufacture isn’t a new idea. Epoxies were first used in car manufacture during the 1960s when they were added to hood assemblies to prevent fluttering, and silicone gaskets replaced traditional materials in the 1980s.