Inline monitoring of cold forging processes using vibration sensors

Multi-stage cold forging processes are used for the mass production of particularly resistant metal products of different level of geometrical complexity. These processes also allow a high degree of dimensional accuracy to be achieved, which can eventually exempt the formed parts from a subsequent machining treatment and therefore lower the overall production costs. Improving the robustness of cold forging processes via digitisation requires the integration of different types of sensors into the manufacturing system. However, the compactness and high geometric precision of the tool, dictated by the high loads involved during the process, and the constraints related to the quality of the final formed part, represent considerable challenges. In this context, externally attachable sensors such as vibration sensors offer a unique perspective. Therefore, this study explored the application of vibration sensors for monitoring cold forging processes. The investigated scenario involved a tool designed for the production of screw-like parts in two stages, comprising a forward rod extrusion and an upsetting stage. Different sensors with inline monitoring capabilities were attached at various locations within the manufacturing system and their recorded signals were analysed, focusing on the interdependence between the part quality, the tool load and the press activity. The results showed that vibration sensors can be used not only for a global monitoring of the press behaviour but also for the local monitoring of the tool load and the quality of the final formed part.