Determination of Tool and Machine Stiffness Based on Machine Internal and Quality Data

During machining, process forces cause form deviations on the workpiece depending on the interacting stiffnesses of all components involved. In order to avoid tolerance violations, it must be ensured that the resulting deflection of tool and workpiece are within the tolerance limit. At the same time, process parameters must be selected in such a way that a cost-efficient and productive production is possible. Stiffness can be determined experimentally by applying a specific force and measuring the resulting deformation. Due to the large variety of tools and tool holders as well as their combinations, it is generally too expensive to determine the stiffness in this way. During quality control, the workpiece geometry is measured, for example, with coordinate measuring Machines (CMM), so that resulting dimensional and form deviations can be determined. Furthermore, there exist approaches to predicting process forces based on machine internal data such as motor currents. In this paper, an approach is presented that enables a determination of the resulting system stiffness at the TCP based on machine-internal and quality data. During the milling process, machine internal data is recorded and a dexel-based material removal simulation (MRS) is performed. Therefore, the estimated force vector is calculated for each dexel. After the simulation, the virtual part is compared with the real part measured by a CMM to determine the deviation vector. By solving a linear equation system, the resulting stiffness is calculated. To reduce the influence of other effects, they are modeled in the MRS or usually reduced so that they are negligible.