New welding technology joins thermoplastics to metal

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The new welding head makes large-area joining of thermoplastic-thermoplastic and thermoplastic-metal possible. (Image: LZH)

A new type of welding head capable of producing nine individual laser spots has been developed.

The technology is designed for welding thermoplastics together, as well as welding thermoplastics to metal, over large areas.

Large laser spots are often used to join thermoplastic over larger connecting surfaces, however, this method usually only introduces energy to the workpiece with a constant intensity distribution. 

When processing curves, this results in too little energy being delivered to the outer area of the curve, while too much energy is applied to the inner area.

The new technology and process developed within the ‘Multispot’ project look to address this issue.

Two partners of the project, Coherent and neoLASE, have developed a diode unit with nine individually controllable diode stacks, with the power of the generated laser spots being independently adjustable. Together with specially developed optics from Sill Optics, another project partner, it is thereby possible to adjust the intensity distribution of the laser light delivered to the workpiece. In this way, the temperature in the weld can be adjusted according to the local thickness and nature of the material, as well as the weld geometry. LMB Automation has combined the components in a welding head, with measuring devices from Primes being used to measure the multifocal optics. 

The new welding head is designed to carry out a process developed by the Laser Zentrum Hannover (LZH) capable of joining thermoplastic to metal.

To ensure an optimal connection, the LZH scientists structure the surface of the metal in advance using a laser. They then heat the metal of the workpiece so that the plastic melts via heat conduction and joins firmly to the metal. Using the process, they were able to successfully join thermoplastic door elements to a metal frame.

The new process could be used for series production in automotive manufacturing, for which its automatability will be important. For this purpose, the LZH scientists, together with LMB Automation, have developed concepts for using the welding head on a robotic arm, and have also written the necessary software programs. As a result, the specified laser power profile can be precisely maintained when moving the robotic arm. Volkswagen provided support in the practical implementation of the new process and technology, and provided demonstrator parts.

The Multispot project was funded by the German Federal Ministry of Education and Research.

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