by Doris Schulz, euroLITE 2008 marketing coordinator
The lightweight construction philosophy is based on the principle of making the best possible use of a material. Many applications demand low-cost solutions that save as much weight as possible, while fulfilling identical or even greater requirements with regard to component properties. Compound casting can meet a range of requirements within one component by combining different materials.
Lightweight construction solutions can be implemented in the design, construction or manufacturing phases. The construction phase also offers great weight-saving potential through the selection of the right material. Often, however, different things are required of a component or material used with regard to strength, corrosion or heat resistance. Components constructed using a hybrid method have proven to be a useful approach.
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Multi-Material Construction
Through the combination of various materials, compound casting can help components meet diverse requirements. And with the hybrid construction process, the material bond is created by recasting—separate hot or cold bonding/jointing processes are not necessary. A good example of an application in this field is the production of engine blocks. As a pure sheet steel solution, it consists of numerous individual parts that are joined together. In contrast, the compound casting solution makes it possible to produce this component as a single piece. An intelligently designed casting made from an aluminium or magnesium alloy ensures high functional integrity of flanges and bearing carriers. In difficult areas, a carefully positioned insert, such as a semi-finished product made of a steel or aluminium alloy, provides the necessary strength.
To optimize weight savings and component strength, the compound casting design must be taken into consideration as early as possible in the design of a mixed-material component. The simulation of the casting process and the evaluation of the compound strength using structural FEM calculations make it possible to precisely tailor manufacturing and the properties of the component to suit requirements.
Types Of Multi-Material Compounds
With form closure, force closure and adhesive bonding, compound casting enables three different types of multi-material connection. While form closure is ensured by the geometric design of the workpiece to be cast, force closure is based on the solidification shrinkage of the casting material to generate a press fit. Each of these material connections has advantages and disadvantages.
The ideal connection must therefore be defined individually for each component. A form closure may lead to a loosening of the connection under dynamic loads, yet it has great static strength. A force closure is only possible if the component can be completely transfused. With adhesive bonding, the properties of the intermetallic phases play an essential part in the quality of the material bond.
Austrian Light Weight Structures, managed by LKR, deals with the assessment of these material bonds by examining the potential and challenges faced throughout the entire product lifecycle. In addition to design guidelines, the aspects of corrosion protection (which is particularly important when two or more metallic materials are used), manufacturing parameters, usability, and mechanical and dynamic properties play important roles. For form closure, the optimal suitability of different geometries is examined; with force closure, the length and thickness of the connection points are optimized; and with adhesive bonding, the kinetics and morphology of the chemical bond are characterized.
Compound casting parts are already used in vehicle construction for parts of the chassis, such as the engine block, shock strut supports and gearbox casings, as well as bodywork components. And according to information from the automotive industry, multi-material components are on the increase. The aircraft industry, too, is relying more on compound cast materials.
The euroLITE fair is the cross-branch and cross-technology fair for lightweight construction. The fair takes place in the Fair Centre of Salzburg, Austria, from June 24 to 26.