Aluminium panels still a cause for concern

Aluminium panels for cars: Thatcham asks if they a symptom of diversification or something else entirely.

Aluminium body structures are more common than ever before and yet they still cause concern amongst both insurers and repairers.

The repair of aluminium structures through to steel/aluminium structures presents a number of options with yet more to come as carbon taxes begin to increasingly affect all.

First up, the reasons. Aluminium is available in a wide variety of alloys as well as a huge range of processes. These include extrusion, stamping casting, low pressure die casting, high pressure die casting, and lost core casting processes. Each offers a unique blend of investment, piece cost, process time and most importantly, material properties.

While it is rare to find a transmission casing that is not made from aluminium alloy, the raw material cost combined with processes related to steel body manufacture can make it difficult to adapt to aluminium (spot welding for example).

Some processes well adapted for aluminium are currently mostly alien to the automotive manufacturing sector (cold bonding for example). This means the material has migrated to higher value vehicles with the exceptions of the Lotus Elise, Exige, Europe, Evora, Audi A2 and the current Audi TT steel/aluminium hybrid body structures.

Theoretically, aluminium alloys can offer better recyclability than steel – currently up to 50 per cent of ‘new’ material can be from recycled sources and could rise further) – which offsets the greater energy input required to extract the metal from the ore in comparison to ferrous materials.

The engineering, however, is the selection of alloy agents to be used combined with the forming process for each point of the vehicle structure. The process of optimising material selection is similar for steel alloys but the engineering is subtly different.

It would be a mistake to mimic steel body construction with aluminium in a price-sensitive sector – the Audi A2 did not reach high volumes while competing head to head with both the Mercedes-Benz A class (W168) as well as the Volkswagen Golf IV.

The reality is aluminium structures can offer significant weight saving for larger more luxurious vehicles. As the unit price increases and potential manufacturing volume decreases, so the opportunity to engineer a body with steel alloys decreases.

Essentially, as Audi A8 has shown over four generations – the latest was introduced in Los Angeles as well as Beijing this year – it is possible to get better component integration with lower tooling investment as long as the business case will stand higher component costs.

So do larger cars have to be engineered from aluminium alloys? No, but it has become associated with the luxury sector in the same way as veneers and perfumed leather have. It is a sign of the new automotive global market that China is one of the largest markets for luxury vehicles – hence the new A8 long wheel base global launch in Beijing.

The thing that turns some of the above on its head is CO2. A larger vehicle will generically require more power and carry more features that weigh more than a conventional mass market car such as Golf VI.

These features include twin AC systems, four fully electrically adjustable seats, 20-speaker sound systems, SatNav that has the ability to play BlueRay DVDs and so on, let alone air suspension or the ability to push passengers into their seats as one accelerates. However, the transient emissions are a huge issue – the luxury sector is not just above the average fleet CO2, it is two to three times the level.

That is why putting electric motors in line with the engine to boost acceleration performance allows the vital CO2 measured during the standard emission test to be reduced. In addition, if the vehicle mass can also be reduced then the CO2 value will fall again. Customers still get a large and imposing car that can also accelerate quickly but they will not pay too much over the odds for the privilege either.

Most vehicle manufacturers in the large luxury vehicle segment are reported as planning to switch to aluminium structures sooner rather than later – Audi, Jaguar and (soon) Land Rover are already there.

Why? Because it makes business sense not only for the manufacturer’s CO2 liability but also for their customers.

Considering all vehicles that have been registered since 1999 – some 25 million cars – just over 300 000 of them are made with aluminium structures, albeit most of those are made with both steel alloys as well as aluminium alloys. However, as outlined earlier this proportion is likely to rise with the luxury segment taking aluminium as the material of choice in the name of better recyclability as well as possibly helping to offset CO2 emissions.

So overall aluminium is unlikely to become dominant – even in hybrid construction – within the next 10 years but will have a greater share of product (rising to around 500 000 units).

Much more commonplace is the application of aluminium for bonnets (pedestrian safety phase1 & 2) doors and boot lids/tailgates. Selective weight reduction conforms to the same process as used for larger structures.

For example, for the manufacturer the effective cap on CO2 may be more attractive for certain non load-bearing external panels, or even for those that have to be able to absorb a predetermined amount of energy (such as a bonnet).

Let us consider the vehicle once it is in the hands of the owner. Firstly who can repair aluminium? Well PAS 125 gives detailed guidelines about what is required in order to process aluminium panels. But there are also further aspects which need to be considered:

CO2 impact: It may well be more efficient to repair a non-load bearing panel than to simply replace. This is a stronger argument for steel alloy parts than for aluminium alloy parts since the recyclability is better (less energy required). This will only come into play once CO2 legislation becomes more visible to the industry (i.e. taxation related to where and how parts were made as well as delivery to point of use).

Training: The techniques used to put together aluminium structural parts into an aluminium alloy structure or a hybrid structure can be quite different from the norm. Impossible? Certainly not but a calculated business decision – yes.

Equipment: Similarly to the training, just ‘having a go’ could produce superficial integrity but not a robust repair. Once again the investment is significant (bonding agents, rivet guns, welders) and so is a calculated business decision.

Given there are fewer vehicles with structural aluminium parts, there are fewer repairers. So getting a damaged vehicle to the repairer may require a longer journey than for a steel alloys body repair.

So the conclusion?

Repair of almost any material in any combination is possible provided the methods are researched, training is undertaken and the appropriate equipment is used. There are no generic solutions. Each vehicle has a unique combination of joining techniques that must be respected to provide the correct repair integrity.

For the future? Any material in any combination is going to become more demanding.
Electric vehicles, for example, are more likely than ever before to use weight-saving materials because the investment in the battery will dwarf almost all other considerations compared to current manufacturer material selection considerations.

For the repairer and the insurer life is going to become very difficult without access to appropriate repair data. ‘Have a go’ really will not work any more.

This article is featured in Thatcham Research News issue 3 2010.