Electric mobility cars require robust body structures, including long-lasting sills and rocker panels. Within electric mobility cars, the sill must have a higher specific mass than internal combustion vehicles, as design and functionality must aid the weight of the battery pack. The sill is usually a multi-layer construction bonded using structural adhesives for added strength and durability. Structural adhesives require specific timeframes of heat – typically in the paint shop e-coat process – to acquire adhesion and mechanical strength.

Challenge

For their next-generation electric vehicle platform, multinational automakers Mercedes used an adhesively bonded steel and extruded aluminium layered sill. During initial developments and testing, the sill had an insulating effect that negatively impacted the adhesive strength and curing properties, both in the body shop and when subjected to the standard e-coat baking processes. Solving this issue required rebuilding the e-coat oven or sourcing a new structural adhesive. The decision was easy, and Mercedes sought help from long-time adhesive supplier and partner DuPont to develop a new structural adhesive with a lower curing temperature window.

Solution

DuPont answered the challenge developing the new BETAMATE™ 1650 broad-bake adhesive. DuPont harnessed their 60+ years of expertise in adhesive technology to craft the perfect solution within a short space of time. Most structural adhesives have a curing window of 165℃ to 200℃. Mercedes required a wider window with a specification of 150℃ for 15 minutes. Performing between Mercedes’ requirement of 150℃ and 200℃, BETAMATE™ 1650 passed all testing as is certified for use.

DuPont responded to the demands for a structural adhesive for new electric mobility cars with a curing window of 15 minutes at 150℃ up to 45 minutes at 190℃ that also had to deliver on the following:

• Adhesion
• Mechanical strength (lap shear, T-peel, and dynamic impact peel)
• Corrosion protection (loss of strength < 30% after ageing)
• Wash-off resistance
• Open time/humidity resistance
• Application with existing technology/equipment
• Shelf life of 6 months

Result 

BETAMATE™ 1650 achieved the desired curing condition that enabled mechanical performance for lap shear, impact peel, and T-peel resistance whilst demonstrating 20% longer fatigue durability against other structural adhesives. BETAMATE™ 1650 also met humidity resistance requirements, even after ten weeks of VDA 621-415 corrosion testing. Mercedes also required a long shelf life, with DuPont delivering a six-month shelf life from when the product leaves the warehouse. 

Sustainability advantages of BETAMATE™ 1650 broad-bake adhesive

New broad-bake adhesive technology allows manufacturers of electric mobility cars to durably bond vehicle body structures using a one-component, body shop adhesive that performs at an expanded curing window: the adhesive cures at temperatures reduced by 20℃ from current standards (160℃). The current minimum curing time/temperature is 12 minutes at 160℃, and the released curing window is from 15 minutes at 150℃ to 45 minutes at 190℃. 

This new adhesive technology reduces the need for sustained e-coat oven temperatures, thus providing energy savings. This technology – with a shelf life of at least six months – demonstrates excellent environmental exposure resistance and delivers high elastic modulus and tensile strength, helping enhance passenger safety by maintaining the quality and durability of the bond throughout the vehicle’s lifetime.