A Viper For Sunday

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?

1992-2002 Dodge Viper

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.

1992-2002 Dodge Viper

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).

1992-2002 Dodge Viper

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.

Ideal for the shopping and school run.

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.

Resin transfer moulding process: source

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.

Author: richard herriott

I like anchovies. I dislike post-war town planning.

20 thoughts on “A Viper For Sunday”

  1. Interesting, where does the BMW,i3 come in this method of construction? I know the carbon fibre part of construction is not injection moulding but are the body panels created by injection?
    There is also the Smart to be considered as the original series had their color throughout the body panels not just blown on the surface,
    Neither of these are low volumn cars.

    1. The body panels for the Smart were made from coloured polypropylene just like your household water bucket, so no fibre/resin artistry in sight here. The non-carbonfibre parts of the I3 are made from p0lyamide, polybutylene-terephthalate and polyurethane.
      BMW at least concluded that it is complete nonsense to invest enormous sums of money into making the body of the car a few kilograms lighter when the car is carrying around several hundreds of kilograms of battery. As a consequence there will be no more battery powered BMW that is built like the I3.

      Injection moulding was used for the hatch of the Fiat Tipo (MK1), bonnet and hatch of the Citroen BX and in a modified form called KMC for bonnet and front wing panels of the 916-series Alfa GTV/Spider. At least the first could be considered mass produced cars.

    2. @Adrian. Yes on the Clio I only the 16S (16V) and Williams had the platic front wings. For the Clio II all versions had those. I own a 20 year old Clio II and a couple of months ago someone parked next to me did some damage to my front wing while getting out of its parking spot. Thankfully I found the missing piece of the wing on the floor, next to the wheel and I stuck it back with strong glue along its edges and put it back like a piece of puzzle.

      The first one to have them was the 5 GT Turbo but the Scénic, Espace, Twingo, Modus and Kangoo also had them.

  2. The Chevrolet Lumina APV (sold in a lot of places overseas as the Pontiac TransSport) had injection molded fiberglass/plastic body panels as well. I think the vast majority of the cars were plastic composite, except the roof.

    This was also the case of all the Saturn cars (S-series, L-series, ION, MK1 VUE) until around 2008, when the car line became more united with Opel/Vauxhall. The MK2 Vue, Aura, Astra, and Outlook were regular steel bodies.

  3. My Citroen AX had a plastic tailgate – among its many lightweight components. ISTR that DTW doesn’t rate the external design of the AX, but I harbour a soft spot for its minimalist design philosophy. If you like that kind of car, it delivered, for its time, quite a combination of performance, economy, ride, handling, and general fun…. though, probably, not the car in which you’d choose to have a big acccident .

    1. I liked the AX design, it was taut and had that tense look about it which I thought portrayed well the car’s nimble performance and fine handling. And that weird spoiler on the plastic tail gate was eveything ! I remember as a kid, when the car came out, I was always looking for that spoiler whenever I spotted the car. The eyes were drawn to it. well my eyes were anyway. I’am still wondering 25 years on if I liked the way they smoothed that spoiler out for the 2nd generation.

      Kudos to Renault though as when their main reason for developing the plastic wings was cost they sold it to the public as an added extra since a lot was done at the time to promote the factthat the wings withstood small impacts and would get their shape back immediately without the paint peeling.

    2. Come to think of it I think the AX looked like an Angry Bird video game character before they were even born.

    3. RichardF: I fully agree with your assessment, and I’m an AX fan as well, especially as it was my first car. Somwhere in the depths of the DTW archive there is an article about this particular vehicle, so we can say that its qualities aren’t entirely unknown at this site.

    4. Add one to the list of AX fans. I wrote a piece which is in the archive here somewhere under the theme of ‘Specials’ I think. I picked out the K-Way at the time, for reasons which I now forget. The AX was sophisticated in its lightness, which did include as you rightly state a plastic tailgate. It was efficient, had an ace gear change, handled excellently and yet rode with aplomb over poor surfaces. I’d love to find a good GT …

  4. Dave: My interest and question concerning BMW i3 and Smart was if the panels were injection moulded which a quick on line search has confirmed to be so.
    As to your remark on BMWs decision it seems to me if one is carrying several hundreds of kilograms (192kg) of battery around any weight savings elsewhere would make sense especially as those enormous investments have already been made.
    I think a more likely scenario will be the combining of the i3 with other lines and looking to greater production numbers which the present design couldn’t accommodate. Watching several on line factory videos of i3 production it seems a very slow process a negative when considering increased production numbers and profits.

    1. Injection moulding of fibre reinforced resin is something completely different from injection moulding thermoplastics or polymers without strands in them. Polypropylene or polystyrene can be injection moulded to extremely high precision and with very good surface quality which puts them in a completely different league from any GRP/CRP injection moulding processes. Just imagine a toothbrush where the hard part of the handle, the rubberised surface including logo and the strands of the head are all moulded in one single step, something unthinkable with fibre based materials.

      The BMW E63’s front wings were polysomething plastic and the Citroen Xantia’s hatch was made from GRP. Renault Espace Mk1 to Mk3 and Avantime body panels were GRP, too, thanks to their Matra origins.

    1. I don’t remember seeing a good technical discussion like this elsewhere for a while.
      The Viper’s process had fibres involved (it seems to be a necessary part of RTM). The Citroens and Saturns were injection moulded.
      The i3 is not unlike Audi’s first A2: it’s a mid-way between special and mass-production. I won’t expect another i3 in the same mode. It was not only about selling cars.

    2. The Smart panels have no fibres, they are made form PP granulate just like a household bucket or a toothbrush.
      Some of the i3’s synthetic parts contain fibres and some don’t.

      A typical injection moulded part made from ABS (coloured) or polycarbonate (transparent) are Lego blocks. They are made with very high precision, good surface quality and show tiny details like the small logos on the dimples. Such parts would be impossible to manufacture from anything containing glass or carbon fibres because the strands prevent such small structures.
      Injection moulded GRP/CRP is a big advantage when compared to hand laminated parts because the process is much faster and quality is much better because a mixture of resin and short individual strands is used instead of large mats that get soaked with resin. The interesting detail is control of length and orientation of the strands because these factors determine the load bearing properties of the part.

    3. Thanks Dave can I assume all the body panels of the i3 are injection moulded with the exception of the roof panel which is carbon fibre as is the passenger cell.

  5. One also has to take into account the form factor of the Viper, I doybt it could’ve been done in metal. Those compound curves need really deep pressings, just look at the curvature of the rear fender. And look how they let form and production restrictives tell where the cut kines should be. I doubt that car could be made with any less panels.

  6. Off-topic I know, but looking at the images above I was struck by the apparent similarities in treatment and surface between the 1991 Viper and Jaguar’s 1994 XK8 around the tail and in the treatment of the rear bumper. Given the timelines, one wonders if perhaps Jaguar’s stylists (Design Director, Geoff Lawson did like his Americana) were inspired by Tom Gale’s studios?

    Another aside: They didn’t spend a lot of the budget on the soft-top did they?

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