What are the categories of precision for machining centers? A machining center refers to a machine tool that processes the surface shape of an object. The precision of processing determines the roughness of the workpiece surface. If the precision of processing is not good, the processed parts will also be defective. So the accuracy of machining determines the quality of the machining center, which can be classified into positioning accuracy, repeated positioning accuracy, geometric accuracy, and cutting accuracy.

Positioning accuracy and repeated positioning accuracy are very important precision indicators, which comprehensively reflect the comprehensive accuracy of each moving component of the axis, especially the repeated positioning accuracy. It reflects the positioning stability of any positioning point within the stroke of the axis, which is the basic indicator for measuring whether the axis can work stably and reliably. When selecting the precision of a machining center, it should be noted that the positioning accuracy is not the machining accuracy of the machine tool, but the accuracy that the machine tool can achieve during machining can be estimated from the positioning accuracy of the machine tool. For example, the hole spacing accuracy of moving two holes on a single axis is about 1-2 times the positioning error of a single axis in that section (the specific error value is closely related to process factors). Ordinary machining centers are capable of processing workpieces with 6-7 levels of precision, while precision machining centers can process workpieces with S-level precision.

At present, countries have different regulations, definitions, measurement methods, and data processing for precision quotas. In the introduction of various types of CNC machine tool sample data, commonly used standards include Germany's VD/DGa3441 standard, the United States' NMTBA standard, the international Iso230 standard, Japan's IsB standard, the national standard GB/JB standard, and the manufacturer's enterprise standard, etc. The accuracy values vary in evaluation and testing. In terms of positional accuracy, some use statistical methods, while others use range methods. Therefore, when selecting, attention should be paid to understanding the precision standards used by the manufacturer, whether the control method for position accuracy of the system adopts direct measurement (closed-loop control) or indirect position measurement (semi closed loop control), and the resolution between the CNC system and control accuracy to ensure the necessary machining accuracy is met.

The geometric accuracy of the machine tool is the basis for ensuring the accuracy of the workpiece processed by the machine tool, and generally does not appear in the technical parameters of the bidding document, but in the acceptance clauses of the machine tool. But in order to ensure the maintenance of machining center accuracy, manufacturers are often required to provide geometric accuracy inspection reports that have been delivered to users to examine the geometric accuracy and accuracy margin of the bidding machining center.

The verification of machine tool cutting accuracy can be carried out based on the inspection items provided by the manufacturer or the trial cut drawings confirmed by both parties. After processing, the dimensional accuracy, shape error, position error, and surface roughness of the workpiece can be inspected.