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Structural Adhesives aka "The Great Facilitator"

Posted on 12/3/2014 1:05:20 PM By Rick Jones
  

Adhesives, in general, are known by a number of different names; glue, cement and sizing are the more common nom de guerre.  Lately, after having read a number of recent articles about Ford’s new soon-to-be-released aluminum body F-150 pick-ups, it struck me that structural adhesives could also now be known as the “Great Facilitator”.

In what many people see as a very bold move to improve the gas mileage of its top-selling vehicle, Ford shed 700 pounds of the F-150’s curb weight by using aluminum body panels instead of traditional steel.  As part of that change, Ford had to totally redesign its manufacturing processes because conventional welding can’t be used on aluminum.  This is where structural adhesives come into play.  The use of adhesives in cars and trucks is hardly new as upwards of 27 pounds of various adhesives are typically used today.  However, the new F-150, though, takes this to another level.

As structural adhesives become more widely used and written about, it’s worth re-visiting a couple areas where structural adhesives deliver value to manufacturing processes, i.e. how they “facilitate” versus mechanical fastening in the making of today’s cars, trucks, combines, lawn movers, etc.

De-Weighting

As already noted, the de-weighting of the F-150 involves using structural adhesives to bond light-weight aluminum body panels.  However, there are many other examples of adhesives facilitating de-weighting, such as using adhesives to bond thin-gage high-strength steels because the heat of standard welding operations causes unacceptable deformation and warping.  Certainly, the use of light-weight but ultra-strong carbon-fiber reinforced plastics in a myriad of applications also dictates the uses of structural adhesives.  There is also a long list of engineered plastics used in auto interiors, sub-components, etc. that require the use of adhesives in their construction and/or attachment.   It obviously goes without saying that adhesives also readily facilitate the combining of many of these disparate substrates where welding is either impractical, creates galvanic corrosion issues or where mechanical fasteners are not well-suited.  Finally, the actual weight of adhesives is far less than that of these mechanical fasteners.  

A side note here regarding the use of these light-weight materials is that manufacturers are not given any waiver when it comes to safety regulations dictated by the National Highway Traffic Safety Administration, the Consumer Product Safety Commission, etc.  While a weld may offer higher tensile strength in a direct head-to-head comparison, the reality is that a bonded structure is able to spread the dynamic load across the entire bond line versus a singular point where the weld is located.  Thus, the use of high-strength lightweight materials and an appropriate structural adhesives does not compromise performance, durability or safety.

Cost Reduction

No discussion about the advantages of using adhesives would be complete if cost reduction wasn’t mentioned.  Now, we could debate the actual cost differences between a rivet, a screw or a weld versus a bead of adhesive, but we’d be missing the bigger story in that adhesives facilitate cost savings in a number of different other ways versus unit pricing.  First, structural adhesives are multifunctional as they provide structural integrity in addition to sealing the part from ingress of moisture, dirt and noise.  In assemblies that are only welded, a separate sealer – with its added material and labor costs – is typically applied to accomplish those tasks.  Another area of savings facilitated by structural adhesives – and one not often fully appreciated – comes from a reduced need for secondary finishing.  As already mentioned, the heat from conventional welding can cause unsightly distortion and/or warping of Class “A” surfaces, particularly in thin-gage metals.  Extra material and labor are then directed toward doing whatever is necessary to eliminate this unsightly problem.  Structurally bonded assemblies avoid this issue all together, thus eliminating these added costs.

While not necessarily a direct cost savings, the use of structural adhesives nonetheless also mitigates a potential future cost associated with corrosion – be it from loss of service or the actual cost of repair.  Because of the high temperatures associated with welding, there’s typically some level of a degradation in the corrosion-resistant characteristics of steel substrates.  While subsequent E-coats and primers can mitigate any lost corrosion-inhibition, the use of structural adhesives in these applications avoids those deleterious temperatures and leaves the inherent corrosion-resistant layer undisturbed.

So, if the goal is to reduce the weight of a product and/or take cost out of the manufacturing process, structural adhesives most definitely need to be part of the solution, as they offer many ways to facilitate achieving those objectives.



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