Investigation Of Positioning Accuracy For CNC Machine Tools

The positioning accuracy of NC machine tool is the best moving position accuracy which the machine tool can reach under the control of NC control system. It's closely related to the process ability of the machine tool. Though current a lot of works have been done on this issue, there are still limitations on the application of theoretical achievements.In this paper, based on fully understanding and deeply analyzing the current status of the research and application of the NC machine tool accuracy and positioning accuracy technique, some experiments have been done and some theories have been studied, so as to find out the root of positioning error for TH65100×100A horizontal machine center, help the factory people to repair the NC machine, solve the technical problems that puzzle the enterprise production.There are several factors that affect the positioning accuracy in accrual produce process. Considering the concrete structure of TH65100×100A horizontal machine center, the influences mostly consist of the full closed-loop feed servo system error, the interfere in production, the thermal error, the geometric errors of machine tool guide way and so on. According to the analysis and elimination one by one, taking the errors of the measurement system into consideration, it points out that the guide way geometric error especially straightness error of guide way is directly related to the positioning accuracy of NC machine tool. After theories analysis and calculation, it's confirmed the influences of the guide way straightness error on the positioning error. At the same time, according to the guide way geometric error change instance by practical observation, the additional analysis are performed to find that the reason of the guide way distortion is the defect in machine tool structure design, which are the stiffness shortage for column base because of the existence of chip area and the residual stresses that are not effectively relieved. The new method of bridge structure installation is used when the guide way are repaired. Finally according to a series of comparison experiments, it's shown that accompanied by the improvement of guide way geometric accuracy, the positioning accuracy of NC machine tool has a marked advance. It's verified by the experiments that the straightness errors of guide way strongly influence the final positioning accuracy of NC machine tool. The conclusion and methods used in this research have reference value and can be learned for others in the industry.