Methods for the design of formed metal parts with printed sensors

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This research proposal aims for plastic forming of printed strain gauges to design innovative products. For this purpose strain gauges are printed on semi-finished metal parts which are formed afterwards. The goal is the production of formed metal products with printed strain gauges that are able to measure elastic strains after the forming process. The investigations are performed for a roll forming application. So far, no strategies for the anticipation of the change in conductivity of the printed strain gauges caused by the forming process are available. Furthermore, no approaches are known which permit temperature compensation of the printed strain gauges after the forming process and take into account their geometric distortion. These gaps will be filled by the proposed project. The goal of the project is the development of methods and guidelines for the design of formed metal parts with printed sensors. The k-factor, which is an indicator for the sensitivity of the strain gauges, depends on geometrical (e.g. cross-sectional area) and material-specific parameters (e.g. conductivity). They can be influenced by the forming process and the environmental conditions. In particular, the influences of the following parameters on the k-factor have to be investigated and an analytical relation has to be derived: temperature, surface texture of the sheet, surface preparation, degree of deformation, strain rate and stress state. The screen printing inks are evaluated in terms of reproducibility of the printed image, the ductility, the adhesion and the scratch resistance. In addition, a test device is designed in which printed strain gauges samples are characterized at low strains. In addition, a characterization after single and multi-axis plastic deformation is performed to determine the variation of the k-factor as function of the above mentioned parameters. Thus an analytical relationship and a guideline for the design of formed metal parts with printed sensors can be derived. The findings are used to design a demonstrator which is produced by roll forming.