The automotive industry is always changing, but perhaps nowhere so much as in automotive adhesive applications—for cosmetics, fastening, and much more.
This isn’t the whole story, though. To say that ‘adhesives are replacing other materials’ would be true, but also somewhat misleading. After all, we’re not really talking about just one product. An automotive adhesive can come in myriad forms:
- Liquids (structural cyanoacrylates or epoxies)
- Sprays (for headliners, fabrics, and rugs)
- Tapes (anti-chipping, mounting, blackout)
- Films (labels, clear bra, vinyl wraps)
- Foams (anti-vibration, cushioning, sound dampening)
- Single-Sided (as in a data label)
- Double-Sided (as in a trim mounting tape)
- Structural (in place of welds, bolts, rivets, screws, or clips)
- Protective (paint protection films, temporary packaging)
- Decorative (paint replacement film, marking film, emblems)
What unites all of these purposes and form factors is that, in every case, modern automotive adhesives can achieve distinct advantages over traditional alternatives. Let’s take a look at the two most pertinent aspects of this shift:
- Which materials are being replaced by adhesives in modern vehicles, inside and out?
- Why are automotive adhesives gaining ground (or even becoming a new standard)?
The answers to these questions, gathered below, are not exhaustive (auto adhesives have a ton of upside!), but they represent the focus of the current market.
Table of Contents:
- Cosmetic Improvements
- Stress Distribution
- No Metal Distortion
- Less Corrosion
- Rapid Assembly
- Cost Reduction
- Dissimilar Material Bonding
- Enhanced Strength
- Vibration Reduction
Which Materials Are Being Replaced?
Cars today are increasingly glued—not screwed—together. Yes, slowly but surely, the mechanical bonds provided by welds, rivets, and other fastening methods are being replaced by adhesive bonds that are superior in virtually every way. For example:
- Adhesives are lighter than the metal fasteners they’re replacing
- Seals (from wind, water, sound) are tighter with consistent automotive adhesive bonding
- There’s less vibration since adhesives don’t rattle and provide more rigidity
- Corrosion is reduced without any punctures or metal fasteners in the panels
- Dissimilar substrates are easier to bond with flexible, gap-filling adhesives
Automotive adhesive bonds significantly cut down on NVH and solve all manner of vibration-related design problems. It might seem hard to fathom a glued-together car being more stable than one secured with steel bolts, but this is often precisely the case.
Today’s structural adhesives also offer stronger overall bonds than mechanical fasteners, in part because they cover the full surface area of the bond (rather than a few finite stress points). Some modern adhesives can offer more than 50 J of impact strength.
Also, automotive adhesives tend to provide the best performance in the face of corrosive agents. Even common chemicals can rust many metal fasteners over time (or otherwise cause them to fail, seize up, or gradually disintegrate). The latest automotive structural adhesives, by comparison, will remain largely unaffected by corrosive elements.
Advantages like these have made automotive adhesives attractive for plastic parts, where they diffuse stresses across a larger surface area and eliminate the buzzing noises that plague lightweight components. They’ve become popular for mounting trim and emblems for similar reasons.
There’s no way around it—the painting process is messy, time-intensive, requires a lot of space and equipment, and can even involve health risks to workers.
Modern adhesive “paint replacement films,” by comparison, are cleaner, faster, easier, and healthier to use in assembly—and they require far less equipment and no separate area for application. Paint alternative films can be applied to parts right on the line.
These benefits, taken together, mean that cosmetic automotive adhesives can save OEMs thousands in their budget. And on top of that, they’re just as attractive as paint (but even easier to replace!).
A great example is blackout tape for door pillars and sashes: it looks just like black paint but saves time and cuts costs on those tough-to-paint components.
Emblems & Trim
Adhesives are commonly relied upon to mount these elements in modern vehicles, but they’re also replacing them entirely, in some cases. Both the interior cabin and the outside of the vehicle are replete with opportunities to save time and money on labeling, marking, or decorative emblems.
Applying an automotive adhesive is much quicker than printing or painting labels onto plastic parts (like knobs and dash elements). But that’s only one of many areas for incredible savings with car interior film. A low-profile automotive adhesive tape or film may even be more practical than a 3D emblem in some areas where snags and shearing forces are expected (or tactile smoothness is desired).
Older (Liquid) Auto Adhesives
Automotive adhesives have played a role in vehicle assembly since the very beginning, but they’ve also changed a lot over time. Many of the older liquid adhesives have given way to easily-applied films and tapes with single and double-sided, fast-bonding adhesive layers. Tapes and films are simpler to dispense accurately than liquid fasteners like epoxies, while simultaneously offering virtually instantaneous adhesion and faster total curing times.
There are other advantages of using a tape over a liquid, too:
- Separate adhesive layers can be selected for each side of the core, to accommodate for the needs of dissimilar substrates—low surface energy (LSE) and high-surface energy (HSE), for instance.
- Tapes can be cut precisely to the shape and dimensions of a part in advance, for the perfect bond every time.
- Most tape and film adhesives are pressure-sensitive—no goo, no mess, no mixing or metering. Just peel and stick (with pressure)!
- Tapes have immediate holding strength, which suits them well for pre-application and staging before a separate piece is joined.
There may have been a time when pressure-sensitive adhesives (PSAs) were not strong enough to compete with epoxies, welds, and rivets, but those days are over.
11 Advantages of Automotive Adhesives
Now that you know where in the vehicle adhesives have made inroads, let’s dive deeper into the why. Below are the eleven principal advantages an automotive adhesive can provide over alternatives in design, assembly, and user experience.
1. Cosmetic Improvements
Automotive adhesives provide aesthetic improvements over welds and mechanical fasteners because they’re entirely hidden between two substrates.
Fasteners like rivets and bolts protrude and can interrupt otherwise smooth panels (on both sides of the surface). Welds leave troublesome slag that requires filing and polishing prior to the painting process. Sometimes lumps and textures from welding are unavoidable, even beneath layers of paint. Even recessed fastener holes would have to be covered somehow to create the appearance of an unbroken surface.
In these situations, an automotive adhesive will streamline the surface and stay out of sight for a sleek, attractive exterior.
Machine Design explains the competitive importance of lightweighting this way:
“Significant fuel savings can be realized by lowering the weight of cars and boats, and any weight reduction may make a product more portable, reduce shipping costs, or allow for installing additional components that give products new abilities and a competitive advantage.”
It’s no secret in the industry that the weight of metal fasteners can really add up. But switching to bonds with lightweight polymers eliminates much more than the weight of the fasteners themselves. In fact, the adhesives are not significantly lighter on their own; it’s how they interact with the substrates that makes the most difference.
Since adhesives distribute the weight of the bond over the full surface area, it’s possible to use thinner panels—the components won’t need to account for weakness from screw holes in the substrate or stress that’s focused at discrete fastening points.
3. Stress Distribution
As mentioned above, a lack of small, discrete fastening points eliminates concentrations of stress around weld spots, rivets, and other fasteners. Whereas a bolt or screw focuses all of the stress of the bond at the tapped or drilled hole in the substrate, automotive adhesives distribute that load over the full surface of the bonded area. The result is a stronger bond and reduced risk of buckling or warping around fastener points.
What can be screwed can also be unscrewed. Loosening of fasteners, substrate shifting, and warping of materials around fastener holes can degrade rigidity over time. Adhesives, on the other hand, ensure a durable bond that will last throughout the life of the vehicle.
The VP of R&D at Sika Automotive, Leslie Wolschleger, explained the benefits of vehicle rigidity to AutoBeat like this:
“Drivers can feel the difference—the vehicle feels more rigid. They don’t know that it’s because of 80 m of adhesive on the car, but they can recognize the improved ways that the car feels when they drive it.”
Look at the 4th-generation Prius from Toyota, which used adhesives to help achieve a 60% boost to the vehicle’s torsional rigidity. The solid, rigid bonds enabled by automotive adhesives paid off with improvements in both handling and driving experience.
5. No Metal Distortion
Rapid heating and cooling from the welding process can cause a host of problems:
- Damage to galvanized surfaces
- Distortion or cracking of metal around the bond
- A weakening of the bonded materials near the site of the weld
- Discoloration or texture changes
Adhesives can achieve the same reliable results without any of these drawbacks, and with far less training, time, and equipment.
6. Less Corrosion
Holes in metal panels can invite problematic corrosion in the substrate or unsightly rust streaking down from degrading fasteners. Fewer holes means fewer corrosion risks.
Scratches, abrasions, and chips in body paint can also result in rust damage. Anti-chipping tapes and self-healing paint protection films are popular automotive adhesives that can prevent these cosmetic problems.
Structural adhesive bonding can help contain corrosion risks, too, since they provide a sealing function (similar to a gasket). At the same time, the layer of adhesive prevents galvanic corrosion from contact between mixed substrates like aluminum and steel.
7. Rapid Assembly
Speed is one of the most impactful conveniences of modern automotive adhesive tape over traditional fasteners, paints, and earlier liquid glues.
One-step adhesives and pressure-sensitive tapes or films require minimal tools and don’t need double-checking for torque after they’ve been fastened. You’ll also be able to skip the drilling and tapping of holes and other surface preparation processes. Welds aren’t any better, with all of the equipment the welder must set up, and the labor-intensive sanding, touch-up, inspection, and other finishing costs.
Tactical use of paint replacement film can cut out drying times that are just as laborious on small parts like door pillars as they are on hoods and fenders. The instant finish of an adhesive could speed up the line up by as much as two days.
8. Cost Reduction
Welding takes training, certifications, inspection costs, and a complicated QA process—high labor costs, overall. Fumes from painting require proper ventilation equipment and create health risks for employees. Fasteners are also expensive to ship and take a lot of space to store (including torquing tools).
Automotive adhesives, on the other hand, can be applied quickly, with minimal equipment, space, or training. The impact on your bottom line can be huge, even before you factor in the faster line times.
9. Dissimilar Material Bonding
Elastic adhesives are a critical tool for accommodating the mixed body composition of modern vehicles. Synthetics and metals have wildly different thermal expansion properties, which can make bonding difficult; changes in temperature will stress the joints and cause buckling around fasteners.
Aluminum, for example, has a temperature expansion coefficient of 21-24, whereas PVC has 54-110. The viscoelastic traits of automotive foam tapes let the substrates fluctuate and flex while maintaining a strong, consistent bond.
10. Enhanced Strength
Methacrylates, cyanoacrylates, epoxies, and other automotive structural adhesives withstand enormous loads. This is why they’re relied upon in aerospace, the automotive industry, and building architecture to form the strongest bonds.
VW incorporated body-in-white adhesive bonding into several Audi models in 2013 to replace welded joints and significantly improve crash safety performance. Today’s structural adhesives can withstand more than 1,000 psi in lap-shear tests (or even up to 4,000 psi) before failing, generally outlasting the substrates themselves.
11. Vibration Reduction
NVH is becoming more important than ever in automotive design. And this trend is only speeding up; electric engines will continue to replace combustion engines. The resulting lack of masking engine sound makes other objectionable rattles and squeaks even more noticeable.
This is one reason (among many) that pressure-sensitive automotive adhesives are rapidly replacing nuts, bolts, and other fasteners that cause vibration-related disturbances. A Grandview Research study from 2015 showed that 40% of the overall revenue share for the NVH materials market came from foam adhesive products alone.
Keep the Pace, or Be Replaced!
These are some of the reasons that cutting-edge auto adhesives are replacing paints, fasteners, welds, and other materials—but they won’t be the last.
Budget and lightweighting pressure on the automotive industry will continue to push OEMs for advancements in all of the above areas. Consult with an automotive adhesive supplier today to see how adhesive products can improve your design project (and your bottom line).