Thursday, 17 March 2016

Challenges to reparability

London region welcomed Andrew Hooker, manager of advanced repair studies & future vehicle engineering at Thatcham to Redhill to discuss the challenges to reparability.

With a remit to investigate technologies being introduced between now and 2045 Andrew was the ideal person to address us on advances that will be introduced or seen in the next five – 10 years.

Matrix platforms are being used by more manufacturers as it saves them money being able to build more models from a common platform.

As there is no common international standard for crash requirements and in order for a manufacturer to be able to sell vehicles in divergent countries while meeting the relevant crash requirements, matrix platforms allow the use of different panel sets dependent on the intended market.

New panel sets give greater flexibility for different markets and powertrains. If sales drop in one market then it is easy to switch to different factories, where production can be easily adapted to suit the existing needs.

Where a common platform is used for different body structures, the greatest challenge to designers is the differing thermal expansion rates between these materials, i.e. between Steel & Aluminium.

The use of adhesive bonding helps to avoid galvanic corrosion.

One way to minimise this problem is to have the join between a body and platform of only two materials, so thermal expansion issues are restricted to one plane only.

In addition to the sometimes conflicting safety requirements, manufacturers must engineer vehicles to meet the emission requirements – which also differ from country to country.

Volvo uses a different platform for one model because the hybrid version has different deformation characteristics to its sister models, as the central tunnel is designed not to deform at all.

The financial pressures on production mean that factories need to be at >90% capacity to be profitable.

But while safety and emission legislation differs from country to country, the requirement to reduce vehicle weight is common to all. With the different technical solutions utilised to achieve this, each one has its own advantages and drawbacks.

Mixed materials and the use of composites are increasingly used in production. However, their use is not limited to being used for structural components, but also in combination with steel and aluminium as hybrid components.

The use of Hybrid panels such as a CFRP boot floor with a common steel surround provides manufacturers with a good solution in production.

Aluminium is liked by design engineers because it is has predictable crash deformation, but it is expensive

Using mixed materials is governed by using the right material in the right place.

Andrew surprised many by stating that recycled Aluminium costs only eight per cent of new material!

Composites have the advantage of being very light and strong and can be easily tailored for any part. They are becoming cheaper to produce and are easy to tailor to suit needs.

The new 7 series is BMW’s first model defined as having a ‘carbon core’ body and the new model reportedly uses SMC and hollow core CFRP reinforcements across the model range. There is no visible CF on the 7 series, and it is understood that where an external steel component is damaged and it has a CF member underneath, then both parts will be changed.

BMW solve thermal expansion issues by joining Steel to Aluminium and Steel to CFRP, but not CFRP to Aluminium due to the huge differences in thermal expansion rates between these two materials!

BMW has invested in SGL and VW also has a 10% investment in SGL, and other car makers including GM, Ford & Toyota are developing use of carbon fibre with Hyundai set to debut a vehicle with CF in 2017.

Joining carbon fibre has challenges where holes are created in the material as it is very difficult to stop the hole from spreading.

The Merge project joins steel to carbon fibre at a molecular level – but it is not known what application this could have.

Laser joining is very good in production for very strong joints, but cannot be replicated in repair. Modern joining techniques are utilised for some B pillars as manufacturers design these to not work in isolation, but to transfer energy further into roof and sill members. Engineers need to be aware of damage caused by transfer of energy resulting further from the initial impact point.

There is increasing use of cast components for suspension components due to strength and cost of production.

‘Hemming’ is a process being used where outer panels are folded over and onto an inner panel with the use of adhesive to expel air. It is suited to where mixed materials are in use and a variation is floating panels where panels are joined in this way with a thicker depth of adhesive that allows some flexibility between the two panels!

Adaptive welding is used to manage the different thermal expansion rates of mixed materials in production, so there are various step changes in weld temperature tailored to the different materials being joined.

Friction element welding involves a unit revolving at 19,000rpm which generates only localised heat and is used in production to join softer Aluminium to hardened steel.

With so many technical solutions in existence it prompts the question as to whether the modular platform sets referred to should lead to modular repair processes which have been agreed by manufacturers to provide a consistent joining strategy for different combinations of materials.

The challenges in repair is clear when considering that there are 53 different materials in the latest Mercedes S Class.

The trend to use external composites and high grade materials may compromise the ability to perform external repairs, with replacement being required in place of repair.

With the manufacturers being fully engaged with emission and safety requirements there is currently no driver for reparability of modern vehicles using some of these existing and emerging production techniques.

Based on the information shared during this event there appears to be an opportunity for IAEA members to engage with Thatcham to highlight and discuss repair issues to build a clearer understanding and strategy to address emerging challenges in repair.

This well attended event proved to be an informative, insightful and helpful interchange between the speaker and all in attendance and appreciation was shown in the customary manner.

Jeremy Taplin