Initial Situation

Plastics have low weight and a high corrosion resistance allied to a high degree of freedom on its form design. These characteristics lead these materials to be used in several technical systems with high product and application requirements. Herewith the complete production chain of these components, as well as their integration in technical systems, are also subjected to high standards.

The joining of plastics is an important step in the process chain, because at this stage preprocessed parts with a high added value are machined. Especially in high performance production chains the usage of joining techniques based on laser transmission welding is technically and financially superior to other methods. This occurs due to its high precision and automation capacity, contact-free, hygienic and absolutely particle-free operation, low temperature and vibration influence, form freedom, as well as short process cycles (no extra cleaning or hardening steps) and the possibility of multi-material joining. Examples are in a broad spectrum of industrial branches, i.e. medical devices (filters, microfluidic, lab-on-a-chip, medical packaging), automotive, pharmaceutics, aerospace, electronics and sensor units.

However this welding method is affected by different machine, work piece and environmental related parameters, which influence the process stability and product quality. For the manufacture of precise and high added value parts with minimal scrap levels and high throughput, the tolerable process parameter deviations are small. To secure process stability and product quality for long production periods, the usage of process monitoring and control systems is consequently indispensable. Most monitoring systems in this field are based on inline pyrometers, imaging systems or the setting path measurement. These methods have a limited usage, as no quantitative information of the real manufactured weld seam as geometry deviation (seam narrowing or interruption) or the presence of pore or cavities is obtained. In the case of medical or some automotive applications a weld seam with a leakage could occur without being detected. These techniques are also limited for weld partners with thicknesses below 2 mm ca. or parts with glass fiber reinforcement lower than 30% per weight and need to be calibrated to every new material or process. Additionally, they are highly sensible to material in-homogeneities. Furthermore, the parameter initialization for new materials and processes is very time consuming. This leads to an increased time to market  and non-productive time of the product.

The main project objective within the MANUNET Weldable project is the implementation of a laser transmission welding controlled by inline optical tomography. This approach enables the acquisition of quantitative information of the weld forming process like detection of weld geometry, pores and leakage as well as the partner gap. This information will be processed and fed back to a control unit, which will adapt in real-time process parameters based on a special developed process and control model with simulative support.