Source: ASI Adhesives and Sealants Industry Magazine – Sept 20, 2020
By: Greg Moran Vice President and Head of Global Automotive Marketing for Sika Automotive.
Advanced sealants and adhesives in vehicle assembly effectively and safely address key applications that have traditionally employed mechanical fasteners while adding design freedom to today’s modern vehicles.
Adhesives have also evolved over the last 100-plus years, in both formulations and applications in vehicle assembly. Advanced sealants and adhesives in vehicle assembly effectively and safely address key applications that have traditionally employed mechanical fasteners (e.g., rivets, welds, screws, and clinches) while adding design freedom to today’s modern vehicles.
The use of adhesives is by no means new, but their growing use enables design trends that even 10 years ago were improbable. Driving the growth of adhesive use are global megatrends in the ever-changing world of assembling vehicles (see Table 1).
Figure 1. Typical automotive sealant and adhesive applications
As illustrated in Figure 1, it is quite easy to see that occupants in today’s advanced vehicles are surrounded by adhesives. And while they are never seen, adhesives are critical to vehicle performance, aesthetics, and comfort.
For adhesive suppliers and users, the selection of products and chemistries is based on multiple factors, including the materials to be joined, joint design assembly method (automated or manual, room temperature or heated dispense), and curing process (heated or cold curing). Further, the performance requirements of the adhesive/substrate interface (i.e., the joint) must be determined. Is the function bonding or sealing, rigid or flexible, crash or non-crash, or general assembly? Performance requirements must also be accounted for, whether the adhesive is located in the body structural assembly or in visible panels and hang-on parts where class A surfaces exist that cannot exhibit bond line read through (BLRT).
Today’s world of mixed materials brings additional considerations with regard to delta/alpha (D/a). Different materials expand and contract at different rates (e.g., aluminum, steel, or carbon fiber). Adhesives can and do play a crucial role in compensating for materials’ different expansion coefficients and, in effect, can serve as the interface allowing for these differentials. Figure 2 shows a basic breakdown illustrating chemistries and performance parameters with overlaps depending on performance requirements.
Adhesive chemistries include epoxies, polyurethanes, methylmethacrylates, rubber-based anti-flutters, PVC, butyls, bitumens, thermoplastics, and in-component manufacturing silicones. Products are chemically cured (i.e., two-component A/B with a base and an activator base), “boosted” to ensure faster rates of cure (polyurethanes), or cured solely by heat or moisture condensation. Adhesives are also rated with modulus-hardness and elongation-flexibility.
Adhesive applications can be organized by the areas where the majority of assembly operations are performed: body shop, paint shop, and trim shop. In addition, multiple sub-assemblies from component suppliers add in at various stations in the process.
In the Body Shop
Widely used in vehicle body shop (body in white, or BIW) assembly applications—and regularly applied in concert with mechanical fixation—hot-cured epoxy technologies are the product of choice. This also holds true for the hang-on parts such as doors, hoods, and liftgates. A variety of product performance ranges are available that are specific to the required applications of sealing, semi-structural, structural, or crash. Products are specification driven, and OEMs typically have similar but slightly differing requirements……….. (Continues www.adhesivesmag.com)
In the Trim Shop
Direct glazing of glass (e.g., windshields, sidelights, and decorative glass) is also accomplished in trim typically using one-component polyurethane-based products. Component assemblies added to the vehicle in the trim shop also benefit from adhesives.
The move toward the use of more and larger glass elements in vehicles such as sunroofs and wide-open panoramic roofs (WOPR), coupled with new combinations of plastics used in their housings, has led to the development of specific chemistries that enable reliable adhesion.
These are fed to the line typically as assemblies, but are installed in trim. New high-performing headlamps, tail lamps, spoilers, antennas, and automated sensing door handles also join the vehicle body here, and all benefit from advanced adhesives use, typically at the Tier 1 component manufacturers……… (Continues www.adhesivesmag.com)
Plataformas Informáticas: 
Automobiles as Computing Platforms.
Today’s sophisticated headlamps require the use of equally sophisticated adhesives to enable long-term performance and fast TAKT time testing at the line.
When we look back several decades, a notable evolution has been the conversion of vehicles to computing platforms with high-performing systems. Accessory systems such as active cruise control, lane departure, back-up cameras, automated park systems, automated braking, traction control, vehicle guidance, infotainment, wireless networking, satellite guidance, and heated accessories such as seats and steering wheels have added more adhesive use to vehicles………..(Continues www.adhesivesmag.com)
Electrification Evolution or Revolution?
The most current megatrend driving automobiles is the electrification of our industry, and only history will decide the correct terminology. While headlines drive the news, the wave of conversion is actively underway. The remaining question is only how consumers will embrace the shift. With electrification, the groundwork is also solidified for the next megatrend.
New vehicles in this class rely on advanced body light weighting for extended range capability and to compensate for the weight of added componentry……… (Continues www.adhesivesmag.com)
Future Growth
- More value-add approaches for assembly using adhesives in automated applications for reduction/elimination of mechanical fixation and labor costs
- Novel product chemistries combining the benefits of multiple chemistries in use today to new baseline formulations with combined benefits
- Continued and increased use of mixed materials require consideration of joining methods that accommodate unique D/a challenges and the elimination of BLRT on Class A surfaces
- Cure-on-demand technologies, as well as allowance for fast fixation similar to spot welding prior to full cure
- De-bond on demand for serviceability, particularly in electric vehicle componentry where service must be performed
- New approaches to acoustic solutions in electric vehicles due to the absence of traditional engine and transmission noise and new frequencies in noise transmission
- Lower bake temperatures experienced by design where heat does not penetrate metals fully, or through sustainability initiatives by manufacturers (utility savings)
- Continued regulations regarding chemical ingredients/formulations and regional moves toward “odor-free” adhesive products (e.g., Europe and China)
- Enhanced use of modeling adhesive performance in “virtual” analysis to predict performance and failure in conjunction with or prior to prototype build levels
There is no doubt that adhesive chemistries’ use and versatility will continue to flourish in enabling the results of the megatrends that continually change our industry.
THE GLOBAL ADHESIVES SUPPLIER BASE IS READY TO MEET THE NEXT BIG DESIGN CHALLENGES.