06 November 2010

Aluminium Recycling Directive

Time Schedule for the ELV Directive

New directives are coming into place that will force manufacturers of products to be responsible for their ultimate disposal. The automobile industry is also subject to these new rules in the form of the ELV (End-of-Life Vehicle) directive. (Ref. Directive 2000/53/EC of the European Parliament and of the Council)

It can be seen from the time schedule that from the 1st January 2006 material recovery from old cars should be more than 85% with more than 80% recycled. The equivalent figures in 2015 are 95% and 85% respectively.

Compared to steel, aluminium is reported to be more recycle friendly and through recycling the value loss from material loss and money value loss is only 22% for aluminium compared to 50% for steel.

Given that automobile manufactures are going to become responsible for the disposal of old cars and if it is accepted that the previous statement on costs is correct, then it is fairly clear that this factor provides an incentive to make more components out of aluminium.

Further considerations for aluminium are that:
  • recycling saves up to 95% of the energy used to produce primary aluminium. 
  • recycling is self supporting by the high value of the material through the recycling loop.
  • the quality of the metal does not deteriorate however many times it is recycled.
  • advanced sorting and recovery techniques are beginning to allow scrap to be suitable for use as primary products such as extrusion ingots and sheet ingots.
These considerations tend to suggest that there is a future potential to use recycled rather than primary aluminium and that this may (by no means definite) lead to reduced costs for aluminium components.

This coupled with the legislative requirements to dispose of old cars through recycling adds even further to the incentive towards the use of aluminium, provided these factors come to fruition, in the future. This is especially true when it is considered that every year end of life vehicles in the community generate between 8 & 9 million tonnes of waste as reported in the 'Directive 2000/53/EC of the European Parliament and of the Council' document.

Ref. P Vigeland (2001)

The information about the European 'End of Life' directive has come mainly from a report by P Vigeland who is the Vice President of Recycling and R&D for Hydro Aluminium rolled products and as such it's possible there is a potential for bias in his report towards the benefits and ease with which aluminium can be re-cycled. However it has been attempted to pick out what is believed to be the factual information from his report rather than theoretical figures which may be misleading, but the onus here is on the reader to asses what they believe to be true.

In any case the underlying principle behind the European directive is that 'the polluter pays' and given the level of waste being produced on a yearly basis and that the responsibility for disposing of that waste is coming back to the doors of automobile manufacturers, this is a factor that definitely needs to be taken seriously.

05 November 2010

Aluminium Cars - Paint Finishing Processes

Aluminium Car Finishes
Because of the nature of aluminium and in order to achieve necessary stiffness requirements in the finished condition, there has been a need to develop new aluminium alloys that can be heat treated after assembly. This particularly applies to sheet material that is typically pressed in its softer T4 condition with the intention of heat treating it as it passes through a paint shop.
Ref. Whiteley, F (1994)

With respect to the painting process itself, Honda discovered during the development of the aluminium bodied NSX that the appearance of metallic paint is affected largely by the type and alignment of the aluminium pigment in the basecoat. One way of improving the alignment is to increase the volume shrinkage rate when drying the base coat.

Water borne base coats reflect much higher shrink rates than solvent borne base coats so brightness can be increased by improving the alignment of the aluminium pigment. However it is necessary to evaporate moisture within the paint that is coated to the body before the clearcoat is applied during pre-heat and this has to be done by force drying.

Audi worked with Dürr, Audi’s general paint shop contractor, to develop a highly automated painting process based on a distributed intelligence and higher-level PC based control system. This enabled processes for new paints and car models to be tested and evaluated.

The process revolves around the supply and removal of air, because variations in air quality and temperature in the paint shop and in baking ovens can greatly impact results achieved for the paint finish.

The system needed to cope with the circulation of air via heaters, heat exchangers and heat emission control systems as well being able to supply and remove water needed for cleansing and removing paint residue in a highly coordinated manner.

Proper control of these various parameters is considered essential so that necessary heat treatments for the aluminium alloy can be performed as well as for optimising the painting processes necessary to achieve acceptable quality levels for the finished paint job.

The flexibility this system provided culminated in Audi being able to apply 15 different series colours and numerous special paint finishes to the body of the A8 despite the problems associated with the painting of aluminium panels.

Painting aluminium, car bodies brings with it a whole new set of difficulties to overcome and as can be seen with some of the other developments in various processes, there has been a need for process innovation to accompany product innovation. In common with many of the other process innovations the adoption of computer technology has played a significant role in presenting the opportunity for much needed increases in the automation levels that seem to be essential for making the developments economically viable.

02 November 2010

Space Frame or Monocoque Structure for Cars

The most popular approach to designing the structural framework for an automobile to date is to use a steel monocoque design. The monocoque is a series of pressed panels which are typically spot welded together to form a self supporting steel framework which is strong enough from which to mount all other component parts of the vehicle e.g. the power train, suspension, doors, bonnet etc.

An alternative to the monocoque is a space frame which is a is a structure of thin walled closed extrusions, typically produced in aluminium, which is bent and twisted to the desired configuration and has thin walled ductile die castings which can be used as attachment nodes or at locations requiring complex changes in section. Sheet aluminium is added as needed for closure of space and shear diaphragms.

It is quoted that this use of the aluminium space frame can result in a 40% weight reduction and an increase in energy absorbing capability compared to a steel monocoque counterpart. The car company Audi believed that this could have been improved to a 67% weight reduction but this would have been at the cost of a reduction in crash safety.
Logic Underlying the Space Frame
  • Closed section aluminium extrusions used instead of fabricated box sections.
    • provides safety in a crash
    • provides frame stiffness
    • provides strength
    • provides durability
    • reduction in number of parts required
Ref. Ashley S. (1994)

Honda attempted to combine the best features of the monocoque design with the best features of the space frame design and produced what they called an aluminium hybrid body structure.

Honda's opinion is that aluminium has major manufacturing restrictions due to inferior press moulding characteristics and difficulties with respect to welding. This leads in turn to the following problems: -
  • An increase in production time
  • An increase in the number of parts used
  • An increase in the number of welding points
  • A large investment in dies to produce the components
For Honda, these considerations form the reasoning behind not simply taking a monocoque design and replacing the steel materials with aluminium. The bottom line is that the problems identified all lead to increased production costs.

If the space frame approach is taken, as it was by Audi in the development of the ASF (Audi Space Frame), it enables the characteristics of aluminium to be utilized more freely, reduces the number of pressed parts required and provides a more rigid structure as previously discussed.

But in Honda's opinion there are drawbacks with simply adopting a space frame design in that there is a requirement for fastening parts/fittings for mounting outer panels and other functional parts. Honda considers that this makes it difficult to meet cost targets.

By optimally combining the 3 moulding methods, Press moulding, Extrusion moulding and Casting,

Honda believed they could gain the correct balance between achieving the necessary rigidity and safety performance in relation to cost savings and productivity.

Honda’s general approach consisted of 3 factors: -

  1. Increased application of extruded materials that could be moulded with complex cross sectional shapes to achieve strength with minimum weight.
  2. Use cast parts to improve coupling rigidity and reduce number of parts.
  3. Reduce number of pressed parts.

Honda claim that they achieved a 15% reduction in the number of parts with 24% reduction in welding points and a weight reduction of 47% for the body in white structure.

Ref. M Saito et al. (2000)

It would appear that the use of the space frame is the predominant approach to car manufacture when trying to utilise aluminium as the primary material. The approaches taken by Audi and Honda in their development activities tend to support this assumption, the underlying logic for both companies are based on very similar perceptions of the problems faced.

Honda may be calling their design an aluminium hybrid body structure but it seems clear that the features are much more closely aligned with those of the space frame than those of the monocoque.