DuPont specialists accepted a challenge from a Tier 1 automotive parts supplier, to make heavy metal liftgates lighter in order to boost fuel economy. Together, DuPont and the supplier developed a customised solution using BETASEAL™ X2500 structural adhesive to bond thermoplastic parts.
Several challenges had to be addressed to ensure high performance, manufacturing efficiency, and the quality of fit and finish.
Joining dissimilar materials
Dissimilar materials with mismatched coefficients of thermal expansion make it difficult to provide a consistent and reliable joining solution. BETASEAL X2500 enabled lightweight mixed-material construction of thermoplastic liftgates for two major global OEMs.
Rapid manufacturing times
For high throughput vehicle platforms, cure times must not slow down production lines. BETASEAL™ X2500 is designed for both room-temperature curing and/or rapid cure rate acceleration through external heating. Infrared heating applied at strategic locations around the perimeter of the liftgate inner panels provides fast polymerisation and green strength development while meeting manufacturing cycle times.
The accelerated curing process of BETASEAL™ X2500 minimises the time between bonding and the performance of subsequent downstream manufacturing and shipping of the liftgate assemblies to automotive OEMs.
Low surface energy substrates
Durable adhesive bonding is a surface phenomenon. This means that the surface energy of substrates influences adhesion. Thermoplastics like glass-filled polypropylene and TPO are low surface energy substrates; therefore, the surface energy of these materials must be raised to enable durable adhesion.
Dimensional design tolerances
Fit and finish challenges are often associated with injection molding of thermoplastic parts. The formulation of BETASEAL™ X2500 mitigated these challenges with an optimal balance of cured properties such as elongation and modulus; enhancing torsional stiffness, and eliminating bond line readout concerns for TPS substrates used on class A surfaces. The tailored material properties of BETASEAL™ X2500 allow for design freedom and optimal gauge thicknesses of substrate materials for maximum weight reduction.
BETASEAL™ X2500 structural adhesive offered a customised solution for the assembly of the injection molded inner and outer liftgate panels that could not be joined through traditional mechanical and thermal joining techniques. Plus, utilising an injection molding process allowed the supplier to reduce liftgate part count by 25-45%, further contributing to mass reduction. The continuous bond line of BETASEAL™ X2500, and the complete joining over complex surfaces and tight radii, imparts enough torsional stiffness to the thermoplastic structures not otherwise achievable by plastic welding or other joining methods. The structural adhesive enables new lightweight thermoplastic liftgates to achieve critical design requirements such as stiffness and fatigue strength durability required of finished product performance.
BETASEAL™ X2500 also improves noise, vibration, and harshness (NVH); impact performance; and component longevity through a continuous and more complete joining of material surfaces. DuPont anticipates that more OEMs will adopt thermoplastic liftgates bonded with BETASEAL™ X2500 because they allow for greater styling and design freedom; more frequent, cost-efficient model refreshes; and they are recyclable.