Adhesive Uses Expanding in Automotive OEM

Posted on 8/7/2018 1:21:41 PM By Dan Murad, The ChemQuest Group

Historically, mechanical fastening and welding were predominate joining methods used in component and automotive assembly.  By the 1980’s, adhesives began making inroads due to the advent of lighter and thinner-gauge substrates, which led to mixed-metal joining, unibody and cab forward designs, and plastic- and ABS-components.  The bonding challenges of lightweighting imposed on OEMs, driven by the increasing pressures of CAFÉ standards, was the driver for adhesive formulators to meet the demand for specific properties in their formulations.

In the last 10 years, OEMs have taken a process-oriented approach when adopting new adhesive technologies. The in-plant directive to “do it right” was commonly heard in automotive OEM piloted adhesive implementations because if the bonding specification did not work, there would be no further opportunity to use, much less optimize, adhesive products.

Fortunately, success was achieved through cooperation and collaboration among engineering, production and purchasing.  Processes were added or changed to allow for designs optimized for adhesive bonding with fewer mechanical fasteners.  Likewise, documenting process parameters became a standard practice, and optimizing curing profiles enhanced adhesive durability.

Today, industry standards for off-line component assembly or on-line body-in-white (BIW) assembly routinely use adhesives not only for joining purposes, but also to improve rigidity, fit and finish, to meet noise vibration harshness (NVH) standards, and to enhance cosmetic appearance. Adhesives are an established protocol of the automotive industry’s 3 to 5-year pre-qualification, qualification, selection, Production Part Approval Process (PPAP) testing and final validation processes.  Consequently, adhesive applications have expanded well beyond traditional uses such as brake shoes, thread lockers, headliners and for installing and repairing windshields (as shown in Figure 1). Now we routinely see applications involving vehicle frames, BIW, dashboards, engines, electronics and weather-stripping applications (see Table 1). Silicone-based electrically conductive adhesives are used in the growing auto sensor technology applications. Cyanoacrylates are used to bond steel clamps to rubber hoses to facilitate assembly.

Table 1:  Automotive OEM Structural Adhesives Uses

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Figure 1:  Windshield installation photo


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Source:  ASC’s OEM Paint Shop, Trim and Final Assembly Adhesive and Sealant Selection Guide (to be released October 2018 on; Depositphotos.

Mature adhesive and sealant materials tend to be dual sourced primarily through procurement officers under contract. Conversely, in the early development stages of new designs, engineering drives adhesives buying decisions especially with respect to emerging technologies. Adhesives are well established and preferred as a fastening method for new designs, which is, of course, good news in the adhesives value chain.  That said, significant vehicle design support, testing and qualification activity is expected of the adhesive supplier. Engineers are working on vehicle designs that will further displace the use of mechanical fasteners and pins – which, in turn, is driving disruptive innovation and growth.

While higher molecular weight 2K epoxies are largely favored in structural applications, lower-curing structural adhesives are on the horizon to accommodate potential reduced e-coat curing profiles.  Weldable epoxies have been developed to allow for weld bonding of critical joints to disperse joint stresses and even aid in sound and vibration damping. The trend will be toward more hybrid applications, i.e., weld-bonding and rivet-bonding, or even hybrid chemical bonding.

Mechanical fasteners and pins aren’t the only joining method being displaced by adhesives – conventional welding is also on the decline. Both Mercedes Benz and GM supposedly have test vehicles with weld-bonded frame rails using a “toughened” epoxy; the plan is to gather all requisite data and work toward eliminating a portion of welds to achieve overall weight and cost targets.

Other market dynamics observed by ChemQuest include:

  • Methodology developed for steel-to-steel assembly is being adapted for use with new material compositions
  • Epoxy systems are favored for weld-through applications, as well as their resistance to the heat of e-coat cure ovens
  • Epoxies also benefit from the cure finishing effect provided by paint ovens in current processes
  • Body components that cannot handle heat are attached post-paint using 2K adhesives (most are urethane). Whereas epoxies are reserved for extreme in-use heat exposure
  • Urethanes are favored for their flexibility and adhesion to SMC and other plastics
  • Each automotive OEM has their own approach to construction materials. Some, like Ford, will embrace aluminum as a primary material. Others will incorporate light-weight SMC or advanced high-strength steel to greater degrees
  • Increased assembly of dissimilar substrates (e.g., steel to plastics, steel to magnesium) in major exterior-to-framing components requires bonding of diverse and dissimilar substrates.

From a materials standpoint, vehicle composition has—and will continue—to dramatically change well beyond 2025.  Mild steel is forecasted to decline, while the use of high-strength, low-alloy steels is projected to grow, the latter being favorable to adhesives, as they do not contribute to heat distortions like welding. Aluminum and magnesium use will continue to increase from current levels, with the use of plastic substrates and components also growing—particularly in body applications.

For more information on the expanded use of adhesives and sealants in transportation applications, including a comprehensive overview of adhesives technologies, uses, applications, and unmet market needs, consider purchasing ASC’s 830-page, 2017-2020 North American Market Report (available here).

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