Minimization of part variation is a challenging and vital research area both in industry and in academia.  Variations in final stamping parts could come from numerous sources such as incoming material properties, lubricant, processing parameters, environment, automation, etc.  Identifying the cause of the variations is not only time consuming, but also a continuously changing process.  In this research project, experiments were conducted to examine the feasibility of implementing closed-loop process control to reduce dimensional variations on an in-production 3D part.  Specifically, the effects of Punch Force (PF) and Binder Force (BF) on part dimensions were studied.  For our particular application, proper control of both PF and BF would be necessary to control the dimensional variations of the part.

        Punch Height and Binder Height were varied in this research while all other process parameters were held constant.  This caused subsequent changes in the Punch Force and Binder Force for the case of varying Binder Height, and only Punch Force variations when Punch Height was manipulated.  The rational for these variations are due to the construction of the double action mechanical toggle press used in this research and extensively in industry.  Then the dimensional variation of the after draw stampings were measured on a CMM.  Results showed that dimensional measurements were affected when Punch Height and Binder Height were changed, in particular for the case of variations in Binder Force.  A small study also showed that variations in material properties effected the dimensions of the parts.

        This work shows the potential to use closed loop control on even the simplistic, mechanical toggle presses found frequently in industry.  The process could be set at a desired Punch Force and Binder Force value.  Then as variations in process and material parameters affect these force measurements, a control system could automatically adjust Punch Height and Binder Height to reobtain the desired values.  The linear relationship between these height and force values would allow these adjustments to be performed easily.  Furthermore, as the small study on material properties demonstrated, the effect of other process parameters would also need to be incorporated into the control scheme.