1992 Mazda RX-792P
Images courtesy and copyright Crawford Composites
Text copyright Michael J. Fuller

Here's a nice composite shot showing the various stages of build that are required to construct the form that  will be used to build a female mold.  The first image shows stations being constructed.  The stations are cut out utilizing 1:1 CAD derived cross sections.  The area between the stations is then filled in with a substrate (generally a polyurethane high-density foam).  Generous use of Bondo helps fill in and smooth out the shape.  Templates are employed to ensure symmetry. 

Nowadays it is preferable to utilize 3-D data and have the form CNC machined via the 3-D information.  CNC machining can lower lead times allowing maximum contemplation for the design process as well as providing maximum accuracy for the form. 

The form is then hard coated and sanded smooth.  Next  the pattern sealed and released, and, depending on what type of tooling is desired, either a viynl-ester coat or carbon fiber strips are applied directly to the surface.  In the case of the viynl-ester, the coat would then be reinforced with fiber glass or similar composite.  The carbon fiber or viynl-ester/fiberglass matrix would then be reinforced with a structure and could then be pulled off the form.  Viola, you have your mold. 

A rear end view of the RX-792P's tub.  From here you can see the relationship between the tub and the ground effect tunnels, the tunnels being integrated into the monocoque's design.  The 4-rotor Mazda powerplant would be cradled in between the tunnels.  You can also get an idea of the material cross section of the tunnels.  The tunnel walls and roof have an aluminum honeycomb core sandwiched between carbon fiber laminates to provide added strength.  Also, check out the assymetrical tunnel sections.  The right hand tunnel has a chamfered off corner in order to provide clearance for the 4-rotor's exhaust system.
The finished product.  Thanks again to Crawford Composites for providing these images.
ęCopyright 1998, Michael J. Fuller
"It's marvelous to go so very fast!"