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Production Technologies and Lightweight Construction Print E-mail
Written by Arjun   
Thursday, 20 September 2007

EMO Hannover 2007 

 Against the background of globally increasing emissions of climate-hostile CO2 gas, the debate on reducing fuel consumption in the field of road transportation is gaining steadily in perceived importance. One of the primary causes of carbon dioxide emissions from cars is seen as the high fuel consumption caused by motorisation and the heavy weight of the vehicles. In order to cut CO2 emissions to the value of 140 g per kilometre demanded by the politicians, purposeful utilisation of lightweight construction strategies for reducing the vehicle's weight and the concomitantly necessary motorisation in terms of vehicle design and dimensioning is appropriate and necessary.

There are three major lightweight construction strategies in common use:
Material-related lightweight construction: replacing the original material by a different material with better weight-specific properties. This can, for example, involve substituting innovative, higher-strength steels, high-strength aluminium alloys or carbon-fibre composites for conventional steel materials.

Mould-related lightweight construction: tailoring the material distribution in the load-bearing structure. By selective matching of the workpiece masses to the stress situation, areas of higher stresses are reinforced, while in low-stressed areas sheet or wall thicknesses are reduced. Examples here include what are called tailored components, which can involve plates welded together from sheets of varying thicknesses or different material qualities.

Condition-related lightweight construction: weight savings achieved by precise analysis of the duty conditions encountered and the reliability of the overall design. By purposefully determining any uncertainties occurring in regard to stresses, the material requirement involved is delimited and reduced in comparison to the original design. Dimensioning-related safety margins can be reduced by more precise knowledge of the duty conditions concerned.

Typically, a combination of all three strategies will frequently be used. For this reason, the term lightweight construction subsumes component dimensioning and design, production planning and technology, plus material science. It accordingly represents a multi-disciplinary engineering design technology that features integrative utilisation of all design, material and production engineering resources reduces the masses and increases the practical utility of an overall structure and its constituent elements.

It should be noted that the application of lightweight construction principles does not necessarily lead to rising production costs for the assemblies or the overall product involved. On the contrary, the material savings or shortened process chains achieved by functional integration enable production costs to be significantly reduced (economical lightweight construction). If we additionally factor in the cost reductions for subsequent operation, an increase in production costs will also be deemed acceptable as a trade-off for reduced fuel costs or increased payload, in aerospace applications, for example. In this case, we speak of eco- or functional lightweight construction. The ratios commonly adduced as tolerated additional costs for weight minimisation are approx. 5 €/kg in automotive construction, 250 - 500 €/kg in aviation and 5,000 €/kg in aerospace applications.

In this context, production technology in general and the development of innovative production processes for manufacturing lighter components in particular play a crucial role. Due to the multifarious boundary conditions applying, from ultra-small series to mass production and component dimensions in the micro and macro ranges, the use of widely disparate lightweight construction strategies assumes economic, ecological and functional relevance.

Current trends in the application of lightweight construction strategies include:

production processes in which the positive properties of different materials are combined (e.g. plastic-metal composites, sandwich components or fibre-reinforced materials),

hybrid production processes in which different manufacturing methods are combined (e.g. hybrid jointing processes or simultaneous forming of a plastic-metal composite),

research into innovative materials (e.g. nano-materials),

advances in computer-aided design and dimensioning strategies (e.g. topology optimisation or factoring in the micro-structure) or

applying principles of bionics for component/product design.
 
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