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Automotive Series: Surface Preparation of Composite Surfaces

Image above: BMW i8 with a body constructed with carbon fiber composite, aluminium and special plastic.


Building a More Fuel-Efficient Automobile

The pursuit to produce a more fuel-efficient automobile does not rely solely on the efficiency of the engine. A great amount of fuel efficiency gains are possible not because of improvements to engine design, but because of improvements in materials. This is an obvious thing to say, but by creating a lighter body, an engine does not require as much energy to move a vehicle forward. Car manufacturers have looked to the aerospace industry for inspiration, and much like modern fighter jets, have settled on the use of composite materials in car frames and interiors to reduce weight. 

As the use of composite materials continues to grow– and even become integrated into more critical parts such as automobile frames--the issue of safety becomes more important. Due to the structure of composite materials, mechanical fasteners sacrifice compatibility. The strength of composite materials dwindles when fibers break due to holes used for fasteners. Rather than using mechanical fasteners, adhesives replace fasteners to bond these composite materials to the frame. These bonds are strong enough to withstand the stresses of a wreck. This allows composite material utilization on critical components of the car frame. That is, of course, assuming the strength of the bond remains consistent – and that is where matters become complicated.

Ensuring a Reliable Bond

When adhering, the surface requires a level of cleanliness in order to produce strong, reliable bonds. Ensuring surface condition and consistency is a vital component for guaranteeing success in sealing, coating, bonding, painting, printing, or cleaning.  All surfaces contaminate upon exposure, and the presence of contaminants is inevitable. But studying and comprehending the relationship between a contaminant structure and the effects it can have on a bond can help develop more productive monitoring procedures for surface preparation processes. It can also effect the development of stronger adhesives and coating formulations.

Experimentation is needed to determine the best method of preparing a surface in a way that maximizes the available surface energy. However, once a method for preparation has been determined many manufacturers have no way of checking a surface on the factory floor to ensure the method's success. That is where the Surface Analyst™ comes in.


Measuring Surface Cleanliness Levels with the Surface Analyst

The Surface Analyst deposits a highly purified drop of water on any surface and determines the contact angle. This contact angle reveals the surface cleanliness level of a substrate. When a surface is clean, it emits high energy; water, as a high energy molecule, spreads out on the surface in attraction to other high energy molecules. This produces a low contact angle. A contaminated surface emits low energy and will cause water to bead up in attraction to itself rather than the low energy surface molecules, producing a high contact angle. By knowing the volume and area of a drop of water, the contact angle of the water against a given surface can be determined. The more contaminated the surface, the higher the contact angle. The lower the contact angle, the cleaner the surface.

Using the Surface Analyst in the laboratory allows manufacturers to develop an effective surface preparation method. Its portability allows for surface testing on the manufacturing floor, ensuring proper surface preparation. Even better, the Surface Analyst™ performs its calculation of average contact angle in a few seconds, reducing delays in the manufacturing process.

With the Surface Analyst™, automotive manufacturers can ensure consistent bond strength between a composite surface and the car frame, allowing them to accurately predict and model how the material will react in a high-stress situation. In turn, this means manufacturers can be more confident in experimenting with composite materials as a way of further reducing the weight of a car, thus increasing its fuel efficiency.

To learn more about developing an effective and fulsome root cause analysis plan, download the Checklist: Adhesion Failure Root-Cause Analysis for Manufacturers eBook. By the end of the document you will have a rich understanding of how to know for certain where your adhesion problems are deriving from and how to put a stop to them.

Adhesion Failure Root-Cause Analysis for Manufacturers