Lotus Elan - An RTM Composite Success

Paper #:
  • 910441

Published:
  • 1991-02-01
Citation:
Vaccarella, P., Jensen, J., and Adams, A., "Lotus Elan - An RTM Composite Success," SAE Technical Paper 910441, 1991, https://doi.org/10.4271/910441.
Pages:
7
Abstract:
With the Elan's launch, Lotus is moving into a new era of low-volume production. By the middle of the next decade, a maximum of 3000 a year will be produced at Hethel and it was these requirements, combined with a desire for more design freedom, that led Lotus to carefully examine its current VARI (Vacuum Assisted Resin Injection) process and develop a unique, flexible system for the Elan.It was decided to develop a manufacturing process to employ a larger number of separate panels to allow future design freedom. The aim was to jig assemble panels which would allow accurate and consistent control of the complete assembly.Evaluation of alternative materials and processes for body panel manufacturing began in 1987, leading to the conclusion that the Lotus patented VARI process was still the most cost effective for the new car.A new patented ‘Fiberform’ process has been developed by Lotus Engineering to provide pre-formed fiber reinforcement which is self-locating inside the VARI tools during the molding process.Parallel to this study, various adhesives were assessed, including epoxies, acrylics and rigid urethanes being used in the motor industry at that time. Results showed that an elastomeric modulus Polyurethane proved to be ideal.In the early 1980's, Lotus developed the paint-in-mold process (VARIP), using non-shrink resins during the curing process to ensure dimensional stability and the absence of surface deformation. Although zero shrink, or low profile, resins have been available since the 1970's, these required a 150°C molding temperature which was not compatible with the VARI process.The search was then on for a low profile resin which could be molded at the more acceptable temperature of 60°C. Lotus evaluated a unique material, AROTRAN™ low profile resin, supplied by Ashland Chemical, Inc. of Columbus, Ohio, USA which met its demands, and this led to the development of the new production process for the Elan.An added sophistication is that the production molds have an electroplated nickel shell surface which not only extends tool life, but also gives a high standard of finish to the body panels, allowing minimal preparation for the painting process. There is virtually no contraction during curing, thereby ensuring excellent dimensional control.It has also been possible to design panels with relatively sharp edges by employing ‘Fiberform’ glass reinforcements.All the outer body panels are a nominal two mm as they are cosmetic and not load bearing. However, there are some exceptions: the undertray, bulkheads, bumper armatures and door inners are thicker to contribute to the structural performance.
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