Examining the Skeleton of the modern motor car.

Volvo S90 body in white. Image: Volvo.media.com.

Call me a Luddite, hurl vitriol to my face, shake your head in disbelief, but one thing cannot be denied. Since strolling onto this site as a wet behind the ears enthusiast, the act of reading, researching and writing about cars has improved my level of knowledge to that of a rounded enthusiast. Few can ever learn everything, but the journey is often more interesting than the destination. And as the saying goes, if beauty is only skin deep, here, the inner beauty of the car is allowed, encouraged even, to shrine through. 

Formula One was something of a catalyst, showing the way with their tyre temperature thermal cameras, often making for more excitement than the race itself. Witnessing those temperatures rise and fall drew me like seagulls to tractor’s rear amid a freshly ploughed field, dazzled as those pale blues and burning reds danced a Celsius Cabriole, if you will.

Obviously we see but the tyre, only the sensors (and cameras) can permit such internal vision. Having these secrets revealed has made me realise just how a tyre delaminates (it’s no real surprise), but having the results literally unfurling before one’s eyes somehow makes it more real. Few people understand how to nurse their tyres; modern racing drivers are often lauded for doing so, eliciting that hard earned victory or being derided for not understanding how the tyre works, thereby triggering an unwarranted pit stop. Consistency and balance are always key.

Image: carthrottle.com.

But turning away from the racetrack to the structure of our daily vehicles, we witness metal being pressed, shaped, formed. As to exactly what metals or, combinations of metals these are, my naive ignorance believed for many years that simple, ordinary steel builds cars. Historically speaking, this was true. Scratching beneath the surface of the modern motor, therein lies the most colourful cornucopia of materials. Well, handily coloured in diagrammatical form only as the body in white on the production line is the uniform silver grey. Without such diagrams, that ignorance of mine might still be having tea and crumpets with rusting hulks.

Take the 2021 Volvo S90 body shell seen in the headline image above. Regardless of the car’s appearance when fully clothed, this image excites not only my inner child for its colourful demeanour but reveals the complex nature of this well engineered, safety conscious model. Had I been on the engineering team I’d have hung this beautiful scene on the wall with its manifest of materials. Feast your eyes on the varying strengths and marvel at just how little mild steel is used. The more tech-savvy could maybe enlighten us as to the differences between very and ultra high strength steel and to where its positioning is applied in the initial roll of metal. 

My understanding of chemistry remains firmly rooted in the classroom some thirty years ago, but I seem to recall that different metals do not take to being combined with others especially well. Uncivilised, unwelcome reactions occur, welding joins adding to the problem, but I haven’t seen a rusty un-accident damaged vehicle in many years so something must be working. 

Alfa Romeo Giulietta floorpan. Image: car.skeleton.blogspot.com

The floor pan of this 2012 Giulietta resembles a plastic model kit. All that’s missing is the sprue where the plastic is injected. But of course every strake, curve, fold, bend and shape is there for a reason. But to these eyes, this pressing is a piece of artwork. I wouldn’t hang it on the wall at home as this would entail all manner of household lamentations (never mind obscuring the TV), though place this in a sculpture park along with an enigmatic title and it could generate enthusiastic comments from those having the sight of Henry Moore.

Hyundai Velostar. Image: car.skeleton.blogspot.com

A car that when fully assembled garners the kind of attention that sees eyebrows furl and metaphorical question marks hover above heads is the Hyundai Veloster. With its quirky triple door affair, this must have taken some midnight oil to achieve in engineering terms. Whereas the Alfa Romeo pressing has integrity and flow, this girder appears brutal, jarring with a heaviness which sullies the impression. No fan of above nor under-surface of this car, am I. 

A wholly different approach, the generation of electric car and its central nervous system. Almost a body scan in appearance, the intricacies shown here would defy any chance of me escaping the labyrinth. Where does one start with planning such a multi-layered, complicated affair? Having no answers to that or indeed any of the above conundrums, I can at least appreciate the endeavours of those blessed with more technical ability than this humble scribe. 

GM Digital Vehicle Platform. Image: Images.hgmsites.net

These images demand deeper looks, thoughts and appreciation. The car contains many levels of fascination for us. While any form of personal transport continues to be made, there will exist conversations and debates as to how the thing looks. But allowing these glimpses beneath the skin helps us understand their inner beauty.  

Author: Andrew Miles

Beyond hope there lie dreams; after those, custard creams?

17 thoughts on “X-Ray”

  1. Good morning, Andrew. Ages ago I read an interview about the development of a Ferrari. I can’t recall the model, but the one thing I remember from that article was that the body was made up of a lot of different materials and that the man responsible for the car expected that number of materials to grow in the future, rather than decrease.

    As far as I know you can’t weld steel straight to aluminium. You can solve this by using a bimetallic transitions between the two metals (basically a piece that’s steel on one side and aluminium on the other. You weld the steel to the steel and the aluminium to the aluminium. Commercially available as FERAN)

    Another solution is bonding, where the bonding material acts as a barrier against galvanic corrosion. I think BMW used this in a number of models.

    1. Galvanic corrosion also described as bi – metallic corrosion.
      Answering Andrew’s question about mild and high strength steel. It’s all about the chemical composition…

  2. For those interested in the finer details of how a car is made today I highly recommend the “Munro live” YouTube channel.
    Absolute car nerdiness guaranteed.

  3. Look at this picture of a tailored blank with steel of different thicknesses and strengths laser welded together as raw material for the stamping process

    1. For someone buying a barn-find from Mathewsons in forty years time. restoration will be a nightmare !

    2. Particularly when you keep in mind thart all those parts are not separate items but laser welded together before they are stamped into form and this form is half the side of a car (the main body section of a Golf sized car nowadays is made up from no more than six pressings).
      Another point is that all those higj and ultra high tensile materials make it extremely difficult formrescue services to cut through them to get ar the passengers. Special (expensive) equipment is needed to cut through door posts or sills.

  4. C8 Corvette “tunnel dominant” (as opposed to “rocker dominant”) mostly aluminum space frame.

    Bedford Castings refers to a GM facility in Bedford, Indiana.

  5. It’s the underpinnings – the platform – that costs the big bucks to develop, of course. Here’s a short film from Volvo on the topic; it’s obviously a very complicated area.

  6. Another interesting article.
    What is especially sad is that all this hidden innovation and engineering will be discarded after three years when the lease runs out and the latest model with a bigger Infotainment screen appears.
    Another interesting point that Dave has touched on is the repairability of these complex frames. I remember seeing a video of two modern Passats that had been deliberately crashed and repaired. One using manufacturer approved methods, the other by a regular bodyshop using traditional methods, not bodging. Both looked identical after the repairs, then they were crash tested and compared with predictable results. The crash performance of the correctly repaired car was comparable to the type test, the other was not. It wasn’t quite a death trap, but wouldn’t protect you half as well. Sadly there was no way of telling one from the other, buyer beware!

    1. Handling all those different materials is one thing.
      The other is replicating the production processes when manufacturers step bs step replace spot welding by laser welding. A current generation Golf contains several dozen metres of laser welding seam which can be done with much higher precision than spot welding but is very difficult for repair shops to replicate in an appropriate quality.
      Another level is Audi’s ASF space frame with connection between cast nodes and extrusions made by bonding the stuff together or making it a stretch fit. Small wonder they set up special certified repair centres for the A8 which are the only ones allowed to replace structural elements. Audi also learned the very hard and expensive way about production processes for mass produced aluminium cars when they came to the conclusion that the original A8 would have needed a relaunch about eighteen months after its production had started and the problems had been sorted out.

    2. I know it’s a stretch but you would hope that Manufacturers would know about stuff like bi- metallic corrosion and how to prevent it. It’s actually been around since God was a boy!

    3. Hello Andrew – yes, this is the video. I’ve seen something similar done with a Ford Focus – a proper repair versus a sub-standard one.

    4. Of course they knew about the different electric characteristics of metals and resulting electro chemical corrosion. The use of zinc anodes on ship bodies was a well established practice long before.
      But some manufacturers didn’t care – think Alfa Giulia Sprint GTA with Peraluman 50 outer panels riveted to the steel substructure without anything between the metals, Touring Superleggera with steel space frames and snippets of leather between the steel tubes and the aluminium outer skin.
      Then look at the BMW E60 with its aluminium nose solely bonded to the steel main body, carefully eliminating all direct contact between steel and aluminium, fully depending on the quality of the bonding for the structural integrity of the car.

  7. Freerk de Ruiter,
    About 1979 we had a Ferrari 275 GTB long nose come into our shop for corrosion repairs. Both doors had aluminum skins with the main door inner shells made of mild steel. The galvanic action had resulted in the outer edges of both the skins and the shells corroding to the point where the skins had begun to separate from the shells.

    As we began working on the doors we discovered the 2 metals had been joined together by folding the outer edge of the skin around the steel shell, a common practice for making all-steel doors. During this process, what appeared to be lengths of flat woven hemp fiber [burlap] were bent over the bare steel edge in a U-shaped fashion. Then the door skin was placed over the shell and the bare aluminum bent over the edge of the shell and crimped tight, trapping the hemp to insulate the 2 metals from each other. No sealant was used to prevent water from entering the exposed seam, so a dozen years later the doors were falling apart.

    We used MIG welding to repair the door shell edge where needed, but the aluminum skins were too far gone, so we hand-formed all new skins. Both metals were primed, using aircraft primer on the skins. A flexible epoxy sealant was used to bond the panels together before the edges were crimped, and as the edges of the skins were crimped into the final shape, we applied more epoxy to seal the completed crimped seam. Saw the car about 20 years later, and the doors still looked great.

    1. Thanks, Bill. I had no idea about the 275’s door, but the way they handled the doors from the factory was a disaster in the making. Using the sealant as you did is a great way of preventing the galvanic corrosion.

      The Ferrari I referred to was a later model, probably somewhere around the year 2000, but I can’t recall the model.

    2. Ferraris from that era were cars where you paid the money for the engine and got the rest thrown in for free.

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