A machining center is a machine tool for machining the surface shape of an object. The precision of processing determines the roughness of the surface of the processed workpiece. If the precision of processing is not good, the processed parts are also defective. So the machining accuracy determines the quality of the machining center, machining center accuracy category can be divided into: positioning accuracy, repeated positioning accuracy, geometric accuracy, cutting accuracy.



The positioning accuracy and repeated positioning accuracy are very important precision indexes, which comprehensively reflect the comprehensive precision of the moving parts of the axis, especially the repeated positioning accuracy, which reflects the positioning stability of the axis at any positioning point in the stroke, which is the basic index to measure whether the axis can work stably and reliably. Should be paid attention to when choosing precision machining center, precision is not processing precision of machine tool, but out of the machine tool positioning accuracy can be estimated when the machine can achieve the precision, such as on the single shaft mobile processing two hole pitch accuracy about single shaft in its positioning error of 1 ~ 2 times (specific error value is closely related to the technological factors). Ordinary machining center can process 6 ~ 7 grade precision workpiece, precision machining center can process S grade precision workpiece.


At present, various countries have different provisions, definitions, measurement methods and data processing of precision indicators. In all kinds of NUMERICAL control machine tool sample data introduction, commonly used standards are Germany's VD/DGa3441 standard, the United States of the NMTBA standard, the international Iso230 standard, Japan's IsB standard, GB/JB standard, and manufacturers of enterprise standards and so on, in the evaluation and detection of its precision value is different. In terms of position accuracy, some use statistical method, some use range method. Should be paid attention to in the selection, therefore, know the what kind of precision standard used by the manufacturer, understand the position precision of the system control algorithm is (closed loop control) are measured with direct or indirect position measurement (half closed loop control), understand the resolution of the numerical control system and control accuracy, to ensure that meet the necessary processing precision.


The geometric accuracy of machine tool is the basis to ensure the accuracy of the workpiece processed by the machine tool. Generally, it does not appear in the technical parameters of the bidding document, but in the acceptance terms of the machine tool. However, in order to ensure the accuracy of machining centers, manufacturers are often required to provide geometric accuracy inspection reports delivered to users to investigate the geometric accuracy and precision margin of bidding machining centers.


The machine tool cutting accuracy verification can be processed according to the inspection items provided by the manufacturer or the drawings of the trial cut confirmed by both parties through negotiation. After processing, the workpiece size accuracy, shape error, position error and surface roughness can be checked.