24 June 2009

Fuel Efficiency in Cars

Auto-mobile manufacturers are looking for new and innovative ways to reduce the mass of auto-mobiles so that they are more fuel efficient and produce less waste emissions.

The problem they face in doing this is that there is a conflict with consumer requirements for better performance levels and new features such as power steering or air conditioning which tend to increase mass.

By comparing steel with aluminium in terms of material properties, it can be seen that it is possible to construct an automobile that is equal, if not superior, in torsional stiffness and rigidity to a steel structured vehicle but at about half the mass with respect to the structural element. Certain design considerations such as material wall thickness and section perimeters need to be taken into account in order to achieve this.

To ascertain if the use of aluminium is suited to high volume production it is necessary to evaluate current manufacturing processes and establish what features, if any, of the processes used in the construction of steel bodied vehicles can be adopted for the production of aluminium structured vehicles.

An initial investigation into the use of spot welding as a joining process indicates that this, although possible, is not ideally suited to joining aluminium components. Similarly the use of closed dies for the stamping of sheet metal panels is not easily transferred to aluminium without taking account of the specific properties of aluminium and can suffer from problems related to spring back and tearing of the material.

These factors lead to an examination of whether there is an alternative structural arrangement more suited to the use of aluminium than the conventional approach of using a unibody/monocoque design. Certainly Audi have opted for a spaceframe approach and have utilised extruded sections joined with nodular castings in conjunction with sheet metal closure panels.

Examination of the processes developed by Audi, Honda and Jaguar tend to suggest that the combined use of bonded joints with alternative welding processes and or mechanical fixing such as pierce riveting can provide a feasible alternative to the traditional use of spot welding.

However for high volume production it has proven necessary for the automobile companies to work with both the suppliers of aluminium and a range of suppliers of production equipment to improve the processes being used and the equipment required to support those processes. This is also true of the finishing processes required to ensure that the material is at its optimum strength and has a high quality paint finish.

Innovation in both product design and in production processes has been necessary to ensure that aluminium structured vehicles can be produced in high volumes cost effectively.