Digital painting with inkjet

„The declared aim of fpt robotics is to supply “automation solutions from a single source„. The company began 40 years ago with the manufacture of plastic tools - today its expertise lies in customer-specific robot and automation components through to holistic factory planning. “We entered the field of digital printing at a very early stage and developed a system ourselves that consists of linkable modules and also includes the logistics of component transport," says Dr. Tim Spiering from fpt robotics.

Applications, e.g. in the field of automotive interiors, increasingly feature 3D geometries and at the same time have to meet increasing design requirements. This is leading to new application methods. In collaboration with the project partner Rippert Anlagentechnik, a flexible laboratory and small series system was created in fpt's technical center, which can be operated in accordance with clean room classification 7. Other components include a 6-arm robot with a spray paint or inkjet head, pre-treatment, cleaning, UV drying and a convection oven. Components measuring 1 m x 30 cm x 15 cm can be coated and printed there under climate-controlled process conditions. Depending on the required movements, larger dimensions are also possible.

Single drops of paint

A really special feature is the new inkjet application process with drop-on-demand technology, where only the paint droplets that are actually needed leave the nozzle. Piezo elements ensure the finest droplets of 10^-12 liters that do not mix. The droplets shoot out of the tool at up to 45 kHz and are applied with high precision in the range of a few micrometers. The process is suitable for 2D and 3D components such as headlight covers, roof elements, handle fittings, steering wheel clasps, covers and fittings. „For us, the focus was on the environmental compatibility of the inkjet process, as it runs with virtually no overspray,“ says Jürgen Rissee from Rippert. „The systems achieve very high quality at a reasonable cost.“

Glass-like surface

The coating is a UV monocure crosslinking 1K solvent-based material from Momentive Performance Materials, the third value-added partner. As the material remains permanently liquid without UV exposure, it is predestined for this application. It later gives the component a glass-like surface hardness and a long-lasting protective function against solar radiation. Thanks to nano components, a very high scratch resistance (resistant to steel wool) can be achieved. In addition, the surface is highly resistant to the yellowing process and to external influences such as moisture and temperature. Momentive carries out appropriate weathering tests for this purpose.

The coating systems have already been approved for the automotive industry and meet all relevant quality standards. „Thanks to their long, intensive practical use, the performance of the coatings is well known and thus represents the constant in the new application process,“ says Thomas Tschurl from Momentive Performance Materials. Processability using the inkjet method - i.e. application via the fine nozzles - is ensured by the appropriate adjustment of the coatings in terms of surface tension and viscosity. Thermally cross-linking coating systems are also currently being tested in the technical center and have already delivered promising results. Matting effects are also possible.

The printed parts are characterized by a high-quality, homogeneous appearance. Compared to spray painting, the drop-on-demand process only paints where it is required - and with micrometer precision. As a result, time-consuming manual masking is no longer necessary. Compared to foiling, the process has the advantage that it delivers high-quality results without stretching, even on component edges and complex shapes.

Another advantage of the drop-on-demand process is its versatility. In addition to paints, color inks and primers can also be printed with the same tool. The fact that the print data set can be changed quickly means that individual parts can be produced at the same cost as mass production.

Preliminary check with software

fpt robotics sees itself as a supplier of complete solutions including the handling of components and/or inkjet application units as well as the corresponding coating supply. A software tool simulates the printing process in advance. This gives the customer a very quick indication of whether the process is suitable for their specific application. Small„, modular solutions can also be realized. For example, the star-shaped arrangement of cells around the injection molding machine for the individual processing steps plus handling tasks.