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Lanxess plastics for hybrid technologies  #10 (80), 2009

Application of new glass-filled PA-6 grades and topological optimization methods allows to develop more effective car copmponents featuring improved design and mechanical characteristics

Prospective technology
The hybrid technology – also known as plastic/metal composite technology – allows to improve product mechanical properties by combining specific strength of plastics and metals such as sheet steel and aluminum. During hybrid part production plastic ribbing are molded onto metal base.
Hybrid technology find wide application in automotive industry for the production of lightweight and highly integrated front ends, which can withstand high static and dynamic stresses. Over 30 million of front ends, for more than 60 models of car, have so far been manufactured from sheet steel and various grades of LANXESS’s polyamide 6.Almost every car maker has models featuring front ends based on these thermoplastics.
Being one of the founders of hybrid technology Lanxess extended the application range of such parts. Along with car roof frames produced from Durethan® BKV 30 H2.0, brake pedal for various vans is also produced. Inner part of the pedal is strengthen with PA-6 ribbing. the pedal can withstand the load up to 3000 N compared to 300 N for fully-metal part, and weights 40% lower. The savings are achieved by avoiding additional assembly stage due to integrated structure of the pedal.
In the case of accident hybrid structure prevents complete pedal destruction; thanks to flexible deformation it can operate even after being damaged.
One more example of Durethan®  BKV 30 H2.0 application is a hybrid pedal bracket for C class Mercedes-Benz. The component's weight is 10% lower compared to fully-plastic one.

The new material
One of the recent Lanxess developments proving hybrid technology advantages is a new high-flow 60% glass filled Durethan® DP BKV 60 EF H2.0 PA-6.
The material has the same melt flow as standard 30% glass filled PA-6 and can be processed under the same conditions. However being twice as stiff (tensile modulus at room temperature is over 19,000 MPa) the material opens new opportunities for hybrid parts design.
During the test carried by Lanxess on Ernalgen block (U-shaped profile with three-dimensional ribbing plastic structure – typical speicement for preparatory technical tests in hybrid technology), it was proved that the new high-filled PA-6 is twice as firm as Durethan® BKV 30 H2.0. A part made of the material can absorb significantly higher energies under stresses.
With the same amount of plastic used for Ernalgen block the speicement made of the new PA-6 is twice flexing resistant as the speicement made of the standard 30% glass filled PA-6.
High-flow PA-6 offers opportunity to produce more light and/or stiff hybrid products. Excellent stiffness also allows to reduce amount of sheet metal in hybrid part.
Lanxess also analyzed the advantages of substitution of conventional 30% glass filled PA 6 with the new material for commercial production of car front ends. Such substitution allowed to reduce weight of the components by 40% and cut production costs by 30%

Topological optimization
Glass filled plastic elements and ribbings of hybrid details are exposed stresses nonuniformly. This means that it is possible to make the areas which undergo lower stresses "thinner" in order to save materials and reduce part weight. And contrawise, the areas which undergo maximal stress should be "thicker".
Topological optimization is a modeling method applied for such parts modification. A program uses the process of iterative optimization for removing plastic from the areas which do not undergo any stresses considering every possible variants of relative stress and direction of part removing from the mold. This defines areas for ribbing and strengtheners. The next stage includes adaptation of corresponding ribbing thicknesses to local stress peaks.
Topological optimization may be used for improving the stiffness of hybrid front ends. After ribbing locations are defined the deformation may be reduced by 20% and during the following ribbing thickness adjustment – by more 10%. Thus the part becomes more stiff by 28% with the same amount of material and the same part cost.
During injection molding of glass filled thermoplastics glass fiber is oriented in various directions depending on part profile and wall thickness, It results in special properties such as setting, stiffness and strength depend on fiber direction. This may cause problems particularly under stresses.
Integrative modeling allows to describe these anisotropic properties in detail and optimize the part in terms of weight and maximum stress.
By now Lanxess has developed the method to such an extent that allows to use it even for complex parts such as oil pans and front ends.

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