by Lotus World Magazine
(no connection with Lotus Esprit World)
With the introduction of the new Stevens' body shape in 1987, a new process was introducted to make the GRP body. This is now formed by the VARI process (Vacuum Assisted Resin Injection). This offers many advantages over traditional hand lay-up but the most significant gain is that up to six bodies a day can be produced from one set of mould tools.
The process begins in the conventional way by coating a female mould with gelcoat. But instead of laying up with reinforcement material and resin, just the dry reinforcement material is positioned on the mould surface along with any polyurethane foam formers that are to be incorporated into the structure. In the case of the Esprit, much of this reinforcement is in the form of CFM (Continuous Filament Mat) but in specific areas woven glass material is employed.
To provide the necessary high strength for roll-over protection, Kevlar reinforcement is used for the roof pillars and sides and, to create a stiff torsion box in each sill, foam inserts are placed into the mould, wrapped in glass CFM. With all the reinforcement materials in place, an inner male mould with an air tight seal around its periphery is brought down under the female mould and bolted into place.
Now the Polyester resin matrix material can be added. A vacuum is applied and this draws resin into the mould cavity from several points. The resin is injected under low pressure and the whole process takes anything from several minutes for a small panel to about an hour for a bodyshell upper or lower half. The vacuum not only draws resin into the laminate evenly, but also clamps the two together.
Because the whole operation takes far less time than a hand lay-up process, faster curing times can be implemented and bodies released from the mould tools much sooner, thus allowing a quicker start to be made on the next car. Curing takes place at room temperature.
Other bonuses are a reduction in labour costs, and more uniform laminate thickness.
The Esprit bodyshell is moulded in two halves the floor section/lower body, and the upper bodywork. Once released from the mould tools, these halves are joined together using a epoxide structural adhesive on the overlapping joint along the waistline of the car. This joint is reinforced in specific areas on the inside by overbonding with glass cloth. Finally, the bodyshell is painted, using two-pack polyurethane paint, and cured in the oven at 80°C.
Once bolted together, the body and chassis create a structure with almost double the torsional stiffness of the basic backbone chassis.