CNC machining accuracy refers to the consistency between the actual geometric parameters (size, shape, and position) and the ideal geometric parameters after machining. In processing, the error is inevitable, but the error must be within the allowable range. Through error analysis, grasp the basic law of its change, to take corresponding measures to reduce machining errors and improve machining accuracy.

There will also be reasons for errors, which are rough as follows:

1. Spindle rotation error.

The spindle rotation error refers to the change of the actual rotation axis of the spindle relative to its average rotation axis at each time. The main reasons for the radial rotation error of the main shaft are the coaxiality error of several sections of the main shaft journal, various errors of the bearing itself, the coaxiality error between bearings, and the deflection of the main shaft, etc.

2. Guide rail error.

The guide rail is the benchmark for determining the relative position relationship of various machine tool components on the machine tool, and it is also the benchmark for machine tool motion. Uneven wear and installation quality of guide rail are also important factors causing guide rail error.

3. The transmission chain is wrong.

The transmission error of the transmission chain refers to the relative motion error between the transmission elements at the beginning and end of the transmission chain. Transmission error is caused by the manufacturing and assembly errors of various parts of the transmission chain and the wear in the process of use.

4. Geometric error of tools.

In the cutting process of any tool, wear will inevitably occur, resulting in changes in the size and shape of the workpiece.

5. Positioning error.

One is the error of inconsistent benchmarks. The datum used to determine the size and position of a surface on the part drawing is called the design datum. The reference used to determine the size and position of the processing surface in the process drawing is called process reference. When machining a workpiece on a machine tool, several geometric elements on the workpiece must be selected as the positioning datum during machining. If the selected positioning datum does not coincide with the design datum, the datum dislocation error will occur. Second, the positioning sub-manufacturing error is inaccurate.

6. Errors caused by force and deformation of the processing system.

One is the rigidity of the workpiece. In the processing system, if the rigidity of the workpiece is relatively low compared with that of machine tools, cutters, and fixtures, the workpiece deformation caused by insufficient rigidity will have a great impact on the machining accuracy under the action of cutting force The second is tool stiffness. The rigidity of the cylindrical turning tool in the normal direction of the machining surface is very large, and its deformation can be ignored. Boring a small diameter inner hole, the rigidity of the toolbar is very poor, and the force and deformation of the toolbar have a great impact on the machining accuracy of the hole. The third is the rigidity of machine tool components. Machine tool components consist of many parts. So far, there is no suitable simple calculation method for the stiffness of machine tool components. At present, experimental methods are mainly used to determine the stiffness of machine tool components.

7. Errors caused by thermal deformation of the processing system.

The thermal deformation of the processing system has a great impact on the machining accuracy, especially in precision machining and large-scale parts machining, the machining error caused by thermal deformation sometimes accounts for 50% of the total error of the workpiece.

8. Adjustment error.

In every process of machining, the processing system must be adjusted in one way or another. Since the adjustment cannot be accurate, adjustment errors will occur. In the processing system, the mutual position accuracy of the workpiece and tool on the machine tool is guaranteed by adjusting the machine tool, cutter, fixture, or workpiece. When the original accuracy of the machine tool, cutting tool, fixture, and workpiece blank meets the process requirements without considering dynamic factors, the influence of adjustment error will play a decisive role in the machining accuracy.

9. Measurement error.

When measuring parts during or after machining, the measurement accuracy is directly affected by measurement methods, measuring tool accuracy, workpiece, and subjective and objective factors.

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