In my 30 years as a senior materials engineering manager with Navistar International, a truck and engine OEM, conventional automotive and truck body manufacturing plants predominantly used 1K epoxy structural adhesives due to their superior bonding performance and manufacturing-friendly properties. The adhesives’ cure is facilitated by the presence of an electro-coat (e-coat) epoxy prime system that is cured at similar temperatures by design. However, many commercial vehicle body manufacturers that are unable to justify the capital equipment expense of a full immersion e-coat system are not able to take advantage of the processing and performance benefits of 1K epoxy structural adhesives. In fact, the manufacturing of a school bus body assembled with mechanical fasteners and 2K epoxy or methyl methacrylate (MMA) structural adhesives is one such example that kept me up at night.
The assembly techniques that school bus body manufacturers use have changed little over time, compared with those of other vehicle body manufacturers. The bus bodies are constructed with flat sheet steel that is pre-coated on a roll coating line. Stamped parts that cannot be pre-coated are individually primed. While fastening methods commonly used in assembly vary by OEM and by application, standard methods for school bus bodies include welding, semi-tubular rivets, self-piercing rivets, sheet metal screws, pull rivets, and pin/collar bolts.