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The next BMW 5-series will abandon the part-aluminium construction of the current model in favour of an all-steel chassis when it is launched next year, Autocar has discovered.

The change is being made for reasons of cost and ease of manufacture. The 5-series uses an aluminium space frame front end, bonded and riveted to a steel rear. It was developed to provide better weight distribution and to cut weight.

But a key BMW insider said that the aluminium structure has proved to be to...Read the full article

I wonder how this will affect the new cars weight? Could there be other areas where they could take off more weight?

 It's a pitty. I'm very sad to hear this.

With alloyed steel making it stronger and lighter using aluminium for subframes etc is almost pointless. The weight savings are pretty low (how much weight does an aluminium bonnet/roof save???) and high tensile steel is pretty strong!

I can't blame BMW, it'll reduce costs massively. If they have a weight saving program aimed at the component level, rather than frame/section level they will achieve better weight savings for lower costs.

Given the weight of the various options added to cars, plus or minus a few kgs. on the base structure is meaningless. For example, why DVD/CD players, DVD-based sat-nav? In the days of the 16GB SD card and iPod this is nonsense. Did I read the Volvo XC60 has a DVD player in the boot!?

Giom37:

I wonder how this will affect the new cars weight? Could there be other areas where they could take off more weight?

The steel manufacturers have had to play catch up over the past couple of years and steel technology has moved on.  With variable thickness and tensile beams and panels. it is often the case that steel can be lighter than aluminium as well as easier to use.

theonlydt:

... The weight savings are pretty low (how much weight does an aluminium bonnet/roof save???) and high tensile steel is pretty strong! ...

The difference in weight between a steel and aluminium body panel is immense. This is starkly demonstrated if you look at the kerb weights of Jaguar’s XJ compared to its S-Type. It’s even more clear if you’ve ever picked up the door and bonnet panels used on cars such as the RS4 and M3 and compared them to the weight of the equivalent panels on the standard A4 and 3-Series.

It’s sad that the current financial climate is effecting industry so severely, and especially the motor manufacture and racing sectors, leaving the sense that we've now left behind forever an era where technological innovation and advancement of the cutting edge was the abiding motivation.

Although maybe out of necessity, it is still lamentable that we now live in more skimping, less exciting times, where the pioneering money-no-object research of Formula One and major manufacturers has been smothered.

If the savings are ultimately in man hours, then I don't believe that there is global saving, but if the cost is due to exotic materials and production techniques, it's perhaps inevitable that future design iterations will follow a cycle of regressive product quality and sophistication.

It's always surprising how quickly the sensibility of the world's population can be radically shifted as a result of a few News reports.

 Teg is right, and so is broom broom - but only in part.  Steel equivalents of existing aluminium bodyparts can easily be produced, perhaps even with a weight saving.  This is not necessarily by producing an identical part in steel, but by redesigning structural elements that sit behind the basic design of a chassis or body panel.  Also note the following:

 

Steel is strain rate sensitive, many aluminum structural grades are not.  It is well known that steel displays positive strain rate performance.  That is, at the higher rates of strain typically associated with crash events, steel has higher strength increases and consequently higher energy absorption at a given part weight. 

Aluminum fatigue performance is less than ½ that of steel. This is a very important advantage for steel in terms of vehicle life durability.  Automotive steel grades also possess an endurance limit.  From testing, it was found that structural aluminum grades (5XXX series) will not reach an endurance limit, but continually degrade at higher cycles.

Aluminum's Formability is approximately 2/3 that of steel (less forming range).  This is a very important advantage for steel for vehicle styling and overall manufacturing robustness

Aluminum's hardness is lower than steel's.  Stone chips and surface quality are harder to maintain for an aluminum body over a vehicle's lifecycle.

Noise, Vibration, and Harshness (NVH).  The ability of any material to attenuate airborne noise is directly proportional to its mass.  Regarding airborne noise, steel clearly has an advantage in most cases.

Steel is magnetic, aluminum is not; very important in recycling end of life vehicles.  Steel is easily recycled because of its magnetic properties versus other nonferrous materials such as lead, copper, zinc, and aluminum.  Thus, Steel separates extremely efficiently, but the nonferous scrap will possess all the unwanted residual materials as well (polymers, glass, adhesive, ceramics, etc.). 

Aluminum's galvanic potential is high, while steel's is low. On an auto body, when aluminum and steel are in direct contact, accelerated corrosion is evident.  There are barrier technologies available to help with this condition when mixing metals, but at a significant cost impact. 

Steel at 210 GPa, has three times the elastic modulus compared to aluminum's 70 GPa.  Steel has three times the elastic modulus as aluminum.  Related to stamping performance, aluminum will possess higher springback than mild steels.  Even compared to high strength steels, strength level to strength level, aluminum will still possess higher springback.

 

A question.

Why has carbonfibre not been mentioned?,its light and in various thickness is as strong as most metals.Why has this material not come down in price? its not new its been around for a long time, time enough for makers to work out costs, to tool up and train people to work with it. Cars would be lighter,stronger, more fuel efficient,and i don't think production problems would be that hard to solve ,like i said carbon fibre be around a long time.Iwould be interested to hear the fors and againsts. 

I would have thought that the ease of repair of steel as opposed to aluminium would be enough reason to use steel. That lovely shiny aluminium alloy spaceframe you were so impressed with in the showroom doesn`t look so good when the bodyshop, instead of saying " it needs a chassis leg, and an inner and outer wing", says " it needs a new spaceframe and they`re £3000 plus we would have to virtually strip the car to fit one, so your car`s written off".                                                                                

As regards weight saving, throw the seat motors away and adjust the thing yourself - that must be cheaper than making alloy spaceframes.

Peter Cavellini:

A question.

Why has carbonfibre not been mentioned?,its light and in various thickness is as strong as most metals.Why has this material not come down in price? its not new its been around for a long time, time enough for makers to work out costs, to tool up and train people to work with it. Cars would be lighter,stronger, more fuel efficient,and i don't think production problems would be that hard to solve ,like i said carbon fibre be around a long time.Iwould be interested to hear the fors and againsts. 

Repair costs.

Carbon fibre, once compromised has to be scrapped.  The costs involved in repairing / replacing a load bearing structure would be prohibitive for a mass production vehicle.

 

Cost cost cost. Why not?

Sourcing, manufacturing, reparability...

The price of the car will fall? ...

PS It is rarely said. But, in 95 % of the cases, an aluminium wheel is heavier than a wheel in steel sheet.

 

Aluminium is ~ 1/3 density of steel.  Although specific strength/stiffness is similar, aluminium still wins weight wise and if you really need to get the kerb weight or centre of gravity down it can be a good option (especially for non-load-critical parts).Regarding the cost of carbon fibre, airbus and boeing have most of the worlds supply (high demand and insufficient supply = highish cost) but the biggest cost is manufacturing - unless you pultrude you will have to manually lay it up, thats where the cost comes from and there are very few options around this atm.  Also, modelling of composites is more complex as is the already mentioned reparability.