EFFECT OF CLEARANCE AND EMBEDDING DEPTH ON SENSING FOR INTEGRATED FORMING PROCESS MONITORING

摘要

In-process measurement of contact pressure distribution across sheet metal-tool interfaces is aimed at improving observability and controllability of sheet metal forming processes through enhanced spatial awareness. Contact pressure variations are determined through spatial interpolation of measurements from an array of tooling-integrated force sensors, by numerical surface methods. The integration of sensors into metallic structures is a challenging issue with limited discussions in the published literature. To gain a quantitative understanding of the effects of sensor integration into metallic mediums, this paper examines two techniques. In the first technique, sensors are integrated into the stamping tool through the top contact surface. Accordingly, the technique is termed as the top mount (TM) method. The second technique, referred to as the bottom mount (BM) method, involves sub-surface sensor installation. The response of a force sensor to surfacernevents can be affected by multiple parameters, such as embedding depth and surface clearance. The effects of these and other parameters on a sensor's response are experimentally investigated in this study, by means of piezo-electric and piezo-resistive force sensors. It is found that sensors embedded using the bottom mount technique demonstrate a linear response to surface loads, whereas top mount sensors exhibit bi-linear behavior. It is hypothesized that the observed bi-linearity is an effect of interaction between the top mount sensor and the sheet metal. In order to evaluate this hypothesis a contact mechanics model has been developed and incorporated into a finite element analysis. Simulation results from the finite element model are in good agreement with the experimental measurements, indicating the validity of the hypothesis. Based on these results, the merits and limitations of the two sensor integration techniques are discussed. The results and discussions presented are relevant for further experimental research and have various potential industrial applications.