This is Part 3 in our series on lightweighting vehicles. See Part 1 for an overview of why and how automakers/OEMs are reducing vehicle weight in the pursuit of lower CO2 emissions.
An important step in achieving lighter-weight vehicles is to replace heavy conventional panel materials (such as steel and cast iron) with lighter-weight materials. Common replacements include high strength steel (HSS), advanced high strength steel (AHSS), ultra high strength steel (UHSS) and alloys of aluminum and magnesium. Polymer composites such as glass fiber reinforced polymer (GFRP) and carbon fiber reinforced plastic (CFRP) are also used.
If you, like many OEMs, are choosing these substrates, you might also consider removing rivets and welds. This is because while conventional joining solutions may sometimes be compatible with composite materials, structural adhesives are the recommended method. Not only are structural adhesives designed to work on these materials, but adhesives are easily adapted to your specific production processes, accommodating factors such as open time and/or cure temperature requirements. Adhesives also provide better aesthetics in the finished panel.
Specialty Area: Hems
Hemming is a method of joining the inner and outer panels of vehicle closures such as hoods, doors, liftgates, trunk lids and fenders by folding the outer panel edge over the inner one. An under-hem structural adhesive must not only provide a strong, corrosion-resistant bond, but must ensure the dimensional stability of the closure panel throughout the entire production process. Reliable dimensional stability affords greater freedom during production, protects the finished part during transportation to other assembly plants—and even improves crash resistance when the part is in-service!
Structural adhesives that can cure at room temperature provide an advantage. For example, aluminum is a commonly used lightweight material but it is not easy to manage through heating processes. Having a two-component (2K) adhesive solution that cures at room temperature with no or low heat gives OEM engineers the freedom and flexibility to better design and manufacture with these lightweight substrates.
Your specially-formulated structural adhesive solution should:
- Bond a variety of substrates.
- Avoid read-through, especially in the case of low-density and thinner gauge composites.
- Form a high-strength bond at room temperature within the OEM process timings.
- Bond through various stamping lubricants without advanced cleaning or surface preparation.
- Require low or no pre-heating.
- Have a high initial handling strength (aids in production processes to improve quality and drastically reduces waste and scrap parts).
LORD Versilok® 273/331 adhesive is an example of a multi-substrate, under-hem structural adhesive that is gaining popularity in the automotive industry. This two-component, epoxy-modified acrylic adhesive bonds a variety of automotive sheet metals, including hot-dip galvanized, electro-galvanized, bare aluminum and cold rolled steel. It can be used across a range of curing temperatures, either room-temperature or heat-cured. Versilok 273/331 is designed with glass beads to provide a strong mechanical lock that will prevent shifting of substrate panels during production processes.