Medical products and biotechnology components make special demands on joining technology used in production. Joining should be performed with as little fillers as possible, and should cause absolutely no dirt and have no effect on the respective materials. The Fraunhofer Institute for Laser Technology (ILT) has now developed a new laser-supported process for the contour welding of high-grade weld seams, which meets these requirements.

Conventional welding processes, such as ultrasound, vibration, and heating element welding in particular, reach their limits with welds on integrated electronic components or micro-mechanical modules, and demonstrate a whole range of disadvantages: The temporal and spatially localized application of energy is limited with this process. The resulting mechanical or thermal loads also damage the parts being joined or cause a loss in their functionality.

Laser beam welding has consequently since pushed to the fore as the process of choice used with plastics. Many applications can now be joined quickly and reliably as a result. With the sealing of micro-fluid structures in particular, as they occur in medical technology, local energy application has proven to be an advantage, because too much plasticization could block the structures.

New developments in medical technology and bio-technology, however, have also increased the requirements of joining processes with regard to miniaturization. The Fraunhofer Institute for Laser Technology (ILT) has responded in this respect with the development of an innovative method.
TWIST (Transmission Welding by an Incremental Scanning Technique) is the name of the new process, which consists of a fiber laser and an innovative irradiation method.

The process unites the properties of contour welding with those of quasi-simultaneous plastic welding. While the main feature of contour welding is the fact that every point of the seam contour only interacts once with the laser irradiation, the advantage of quasi-simultaneous welding is that, despite the high feed rate of this process, a high level of seam contour flexibility is still guaranteed.

The new TWIST irradiation method functions in such a way that the laser radiation is guided along the feed motion on a circular path, and every contour increment, i.e. every tiny section of the contour, is passed several times. This overlapping at speeds of 4 m/s means that joining geometries with widths smaller than 100 µm can be achieved, as they are required for producing medical technology diagnostics chips, for example. A series of advantages emerge here with regard to the weld seam: Firstly the high path speed within the contour increments results in a homogenous energy application over the length of the weld seam. Fluctuations in the seam width and depth can consequently be prevented. Secondly the depth of the heat affected zone is significantly reduced, which means that the weld seam is not visible on the rear of the work piece.

On the whole, therefore, the TWIST process is especially well suited for use in medical technology because it has a flexible weld seam setting between 100 and 500 µm, and with its high speed it also meets the industry's requirements, generated by having to turn out high production numbers.
Another TWIST area of application would, of course, be the automotive industry, where the irradiation method could be used for welding plastic components, both with the assembly of fender components and with interior paneling elements.