Closure of the research project »Analysis technologies for multi-stage processes«


The research project »Analysis technologies for multi-stage forming processes using sensorial fasteners and Data Mining Tools« has been successfully completed at the end of April 2015

The product portfolio for multi-stage processes is characterized by high component complexity, integrated component functionality and strict quality requirements. The automatically linked processes are characterized by high investment costs and productivity. In production, the mechanisms of error emergence and propagation in interlinked stages are often unknown. Up to now there were no measurement technique that allows to capture physically clear readings with a reasonable effort. The ConSenses GmbH developed a bolt with integrated sensor element, that is able to capture the bolt additional force. This PiezoBolts can be installed in accordance with a conventional bolt and additionally can be used as a force sensor.

With the PiezoBolts of the ConSenses GmbH a multistage tool of the Werner Schmid GmbH was equipped and monitored in series production. The PiezoBolts were mounted close to the process in the individual stages. Therefore, the recorded force curves reflect the process force curve in very good quality. First, the detection of a reference curve during an ideal process, free from errors, was carried out. This reference curve was stored in the analysis software of the ConSenses GmbH and was compared with the values recorded during the series production. As in the case of a process fault, the process force curve deviates from the reference force curve, all process failures could be detected clearly.

The PtU created numerical models of the first three deep drawing stages and the upstream cutting stage of the monitored tool. By linking the steps to one another in the FE, it was possible to consider the error propagation within the stages.

In an FMEA, executed by the PtU, an surface defect was identified as a critical process error. Opening of the shrinkage holes was suspected by the Werner Schmid GmbH to be the reason of this error. Based on this assumption, a shrinkage hole has been modeled in the simulation as two-dimensional space in the metal sheet. It was found that this void, which is in the side area of the cup, widens in each forming stage and eventually ruptures to the component surface. Therefore, the simulation confirmed the shrinkage hole to be the cause of surface defect.

During the project a geometry error of the cup has been identified as another error which develops in the first deep drawing stage. By the use of PiezoBolts and by the creation and evaluation of realistic FE models of the respective forming stage and the upstream cutting stage, the cutting process could be identified as the error cause.

The simulation results were also used to confirm the validity of the measurement results. As the measurement results corresponded very well with the simulation results, it could be noted that they were not affected by both the press or the tool.

Thus, the aim of the project to install a reliable measurement system and to test it in series production was achieved.

The research project was funded via the Hessen Agentur GmbH by the state Hessen.

We would like to thank Werner Schmid GmbH and ConSenses GmbH for their cooperation.