When designing the Elise, Lotus made the decision to use an aluminium spaceframe to both save weight and enhance performance. Instead of conventional joining techniques it was decided that adhesive bonding would be the best method of providing accuracy through elimination of weld distortion, repeatability and simplified tooling requirements.
The bonding process was developed in partnership with Ciba Polymers (Switzerland) for the adhesive and Hydro Aluminium (Denmark) for both the development of the extrusions and of the bespoke pre-treatment anodising process which enabled the components to be directly bonded to a robust architectural grade metal surface which required no subsequent protection coating.
TWI was consulted by Lotus on the long-term testing and conditioning programme with respect to the data generated and the resultant failure surfaces obtained from destructive testing. The analysis showed that the bond properties significantly exceeded the performance requirements of the car, even after extensive periods of extreme outdoor weathering.
Additionally, as part of TWI’s CRP programme, the adhesive developed for this application (XB5315), was assessed in considerable detail to understand its exceptional toughness with respect to morphology and mechanical testing.