Nought to sixty in under 5 seconds, courtesy of a V10. No door handles. What do people do with cars like this in Denmark, I have to ask?
I really don’t know. What I do know is that cars such as this are where there is overlap between the mainstream mass manufacturers and the fringe enterprises (covered since July 2016 with forensic thoroughness in the celebrated Far From The Mainstream series). The difference is that large-scale manufacturers can call on the expertise of seasoned car designers and costly, advanced specialist manufacturing processes.
Absolutely everyone who wants a car like this to will surely be aware that resin transfer moulding forms an essential part of its manufacturing process. You would not make a car looking like this from steel.
Resin transfer moulding requires two materials to be mixed during moulding. One is a resin and the other is a curative (not unlike the way Epoxy resin is sold in two packs and only when these are mixed does the material solidify).
Two compounds are injected into the mould after being mixed in a chamber en-route from the supply. In the mould which might be two or more parts held together by clamps there is a preformed mat of fibres. The mix fills the void and solidifies around the mat.
Transfer moulding uses a heated mould and higher pressures than injection moulding. The heated mould ensures that the material remains liquid until the mould is fully filled. Further, cooling can be controlled so that the object forms without sink marks, those ripples you may see on cheap plastic items.
You will notice that the Viper has no sharp feature lines (like the glass fibre bodies of later TVRs). This is due to one of the limitations of RTF which is that the fibre mats limit the minimum size of the radii possible.
Composite Integration provides a handy list of the features of RTF:
- Volatile emissions (styrene etc) are massively reduced.
- It can be a fast, clean and repeatable process.
- The laminate thickness can be closely controlled.
- The process is far less reliant on the manual skills of the operator.
- The ‘B’ surface of the moulding can be accurately defined.
- The process can be automated.
This brings me to an interesting diagram I have invented. It shows the circular relation between material, appearance and process:
In this instance, the choice of material (composites) has dictated the process (the two are closely interlinked) which in turn has determined the radii of the surfaces. You could add to this three-way diagram “function” which will determine material selection as well. Tacit in this diagram is the business of cost and quality.
Dodge required a low unit cost in relation to the expected production runs. Had production volumes been similar to a mainstream saloon, RTF would not have been economically feasible. The process also had to result in an acceptable quality which probably militated against glass fibre bodywork (which is also more labour intensive).
Composite bodies are not merely of historical interest. The Financial Times reports that the growing electric vehicle market means there is a renewed interest in alternatives to metal bodies. “Composites such as carbon fibre reinforced plastic can be tailored to be 10 times stronger than steel or a fifth of the metal’s weight”, reports the FT.
Which brings us back to the cost element unmentioned in the three-way diagram above. For composites to be practical they must be affordable which is why, for the moment, they are still only a small element of car body construction. However, in due course the unit costs will fall and the technical limitations described here will be removed – design drives manufacturing processes.
Designers wish to do what current manufacturing can’t and a good engineer does not say “we can’t do that”. She or he says “we can’t do that yet – but give us time and we can”. And that is why cars today don’t look like cars from 1991.
You can find a nice précis of the evolution of materials in the car industry here.