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Lecture

Al-Cu and Al-St Bimetal Wire for Lightweight Structures

Friday (10.11.2017)
09:55 - 10:15
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Several fields of engineering would have been unthinkable without bimetals. They can be made by cold or hot roll bonding, extrusion of composites or centrifugal composite casting, and are used as connecting elements, fasteners, or as bearing materials. Bimetals can combine properties in a semi-finished product, a combination which cannot be achieved with a single material on the one hand. On the other hand, high quality materials can be used more efficiently and more economically.

Bimetals are produced as strips or sheets. This results in labor-intensive machining and is thus costly for applications that demand very slim geometries such as for electrical connection elements or transition joints. Thin, wire-shaped bimetals are commercially available only as fully coated round wire. Rectangularly-shaped wires for small final sizes would be much more favorable for economy.

The manufacturing process of rectangularly-profiled bimetal wires by means of laser roll bonding was developed by the Fraunhofer IWS and subsequently patented. Both wires (with an edge length of up to 5 mm) are guided to the pass at an angle of 45 °. The internal wire surfaces can be heated to process temperature immediately by a rectangular high power laser beam. The highly concentrated and localized heat input means that forming only occurs in these areas. Both initial wires can be tempered by preliminary inductive heating. To guarantee a homogeneous deformation across the entire cross section of the wires, a roller couple designed as a »closed caliber« is used, they form the desired bimetal contour. The process results in very small total deformation ratios in order to generate highly loadable bimetal wires.

Depending on the deformability of the bimetal-compound, narrow butt joints of 1 mm thickness are also feasible. They can be used as transition joints in several mechanical or electronics applications. A preliminary contour is made by laser roll bonding; then it is rotated by 90 ° and rolled to the final contour afterwards.

In laser roll bonding brittle phases are not or only partially formed, which is quite advantageous and provides high-strength material composites with good cold formability – even for material which strongly tend to form intermetallic phase borders.

 

Speaker:
Andrea Berger
Fraunhofer Institute for Material and Beam Technology IWS Dresden
Additional Authors:
  • Volker Fux
    Fraunhofer-Institut für Werkstoff- und Strahltechnik IWS

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