Integration of machine tool specific capability information related to a manufactured part’s accuracy can significantly support the decision-making in production, help to understand root-cases of quality loss and optimize cutting processes. In this paper, a systematic methodology is proposed to bridge the gap between machine tool specific capability and finished part’s accuracy. For this purpose, a measurement-based model is implemented in a CAx software environment for the prediction of geometrical deviations in complex milling processes. Results are presented in a case study to demonstrate errors on the workpiece level due to the quasi-static capabilities of a given machine tool.

Detailed description of multi-axis repeatability performance and modelling of non-systematic variations in the positioning performance of machine tools can support the understanding of root-causes of capability variations in manufacturing processes. Kinematic characterization is implemented through repeated measurements, which include variations connected to the performance of the machine tool. This paper addresses the integration of the positional repeatability to kinematic modelling through the employment of direct measurement results. The findings of this research can be used to further develop standardized approaches. The statistical population of random errors along the multi-axis travel first requires the proper management of experimental data. In this paper a methodology and its application is presented for the determination of repeatability under static and unloaded conditions as an inhomogeneous parameter in the work space. The work is exemplified in a case study, where the component errors of a linear axis were investigated with repeated laser interferometer measurements to quantify the estimated repeatability and express it in the composed repeatability budget. The conclusions of the proposed methodology outline the sensitivity of kinematic models relying on measurement data, as the repeatability of the system can be in the same magnitude as systematic errors.

Machine tool testing and accuracy analysis has become increasingly important over the years as it offers machine tool manufacturers and end-users updated information on a machine’s capability. A machine tooĺs capability may be determined by mapping the distribution of deformations and their variation range, in the machine tool workspace, under the cumulative effect of thermal and mechanical loads. This paper proposes a novel procedure for the prediction of machine tool errors under quasi-static and loaded conditions. Geometric errors and spatial variation of static stiffness in the work volume of machines are captured and described through the synthesis of bottom-up and top-down model building approaches. The bottom-up approach, determining individual axis errors using direct measurements, is applied to estimate the geometric errors in unloaded condition utilizing homogeneous transformation matrix theory. The top-down approach, capturing aggregated quasi-static deviations using indirect measurements, estimates through an analytical procedure the resultant deviations under loaded conditions. The study introduces a characterization of the position and direction dependent static stiffness and presents the identification how the quasi-static behavior of the machine tool affects the part accuracy. The methodology was implemented in a case study, identifying a variation of up to 27% in the stiffness response of the machine tool. The prediction results were experimentally validated through cutting tests and the uncertainty of the measurements and the applied methodology was investigated to determine the reliability of the predicted errors.

Modelling of non-systematic variations in the positioning performance of machine tools can support the understanding of capability variation in manufacturing processes. Kinematic characterisation is implemented through repeated measurements, which include variations connected to the performance of the machine tool. This paper addresses the integration of the positional repeatability to kinematic modelling through the utilization of direct measurement results. The statistical population of random errors along the single-axis travel first requires the proper management of experimental data. In this paper a methodology is presented for the determination of repeatability under static and unloaded conditions as an inhomogeneous parameter in the workspace. In a case study the component errors of a linear axis were investigated with repeated laser interferometer measurements to quantify the estimated repeatability and express it in the composed repeatability budget. The conclusions of the proposed methodology outline the sensitivity of kinematic models relying on measurement data, as the repeatability of the system can be in the same magnitude as systematic errors.

For proper characterisation of different physical quantities in machine tools, it is necessary to report the uncertainties associated to the measurements. The uncertainty evaluation, according to international standards, expresses information of the quality and the reliability of the measurement result. Applications like calibration and compensation are sensitive for the quality of the input data, thus the reliability of the characterisation results need to be interpreted accurately to avoid significant residual errors or overcompensation. General approaches take several factors into consideration during the estimation of measurement uncertainty such as the environmental variations or the uncertainties of the measurement device or the setup. At the same time, various reproducible and non-reproducible error sources associated to the performance testing of the machine tool are ignored. The reason behind it can be the lack of the applicable standardized measurement instruments.

This paper highlights the significance of the uncertainty sources connected to the performance of the machine tool under quasi-static loaded condition. The variation of the static stiffness of machine tools, the hysteresis and play in the system can be even more significant uncertainty sources than the above mentioned ones. Under the framework of elastically linked systems (ELS), a circular test device, the loaded double ball bar (LDBB), is used in a case study to identify this effect. The LDBB can be used as a double ball bar, with the additional capability of applying a load, thus it enables the measurement of machine tool deviations under quasi-static loaded conditions. A measurement methodology is proposed to properly describe and demonstrate the variation of the contributing uncertainties associated with repeatability performance of the machine tool. With this approach important interdependencies can be expressed as uncertainty sources.

One of the greatest challenges in the manufacturing industry is to increase the understanding of the error sources and their effect on machine tool capability. This challenge is raised by the complexity of machining systems and the high requirements on accuracy. In this paper, a mechanistic evaluation approach is developed to handle the complexity and to describe the underlying mechanisms of the machine tools capability under quasi-static condition. The capability in this case is affected by the geometric errors of the multi-axis system and the quasi-static deflections due to process loads. In the assessment of these sources a mechanistic model is introduced. The model is composed of two parts, combining direct and indirect measurements. The direct measurement modelling method was applied to predict the effects of individual axis geometric errors on the functional point of machine tools. First, the direct measurement is employed to allow measuring each single machine tool axis motion error individually. The computational in the direct measurement model calculates the deviations from a given toolpath in the work space. Then, indirect measurements are used to determine the static stiffness and its variation in the workspace of machine tools. A case study demonstrates the applicability of the proposed approach, where laser interferometry was implemented as direct and loaded double ball bar as indirect measurement. The methodology was investigated on a three and a five axis machine tool and the results demonstrate the potential of the approach.