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The main reasons for CNC precision machining errors

It refers to the degree of conformity between the actual geometric parameters (size, shape and position) of the part after machining and the ideal geometric parameters. In machining, the error is inevitable, but the error must be within the allowable range. Through error analysis, the basic laws of its changes can be grasped, and corresponding measures can be taken to reduce machining errors and improve machining accuracy.

Then there are also reasons for the error, which are roughly as follows:

1. Spindle rotation error.

The spindle rotation error refers to the variation of the actual rotation axis of the spindle relative to its average rotation axis at each moment. 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 the bearings, and the deflection of the main shaft.

2. The guide rail is wrong.

The guide rail is the benchmark for determining the relative positional relationship of various machine tool components on the machine tool, as well as the benchmark for machine tool movement. The uneven wear and installation quality of the guide rail are also important factors that cause the guide rail error.

3. Drive chain error.

The transmission error of the transmission chain refers to the error of the relative motion between the transmission elements at the head and tail of the transmission chain. The transmission error is caused by the manufacturing and assembly errors of the various components of the transmission chain and the wear during use.

4. The geometrical error of the tool.

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

5. Positioning error.

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

6. Errors caused by forces and deformations of the process system.

One is the stiffness of the workpiece. In the process system, if the rigidity of the workpiece is relatively low compared to the machine tool, tool, and fixture, then under the action of cutting force, the deformation of the workpiece due to insufficient rigidity will have a greater impact on the machining accuracy. . The second is the 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. When boring a small diameter inner hole, the rigidity of the tool bar is very poor, and the force and deformation of the tool bar have a great influence on the machining accuracy of the hole. The third is the rigidity of machine tool components. Machine tool components consist of many parts. To date, 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 process system.

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

8. Adjustment errors.

In every process of machining, the process system must be adjusted in one way or another. Since the adjustment cannot be absolutely accurate, an adjustment error occurs. In the process system, the mutual position accuracy of the workpiece and the tool on the machine tool is guaranteed by adjusting the machine tool, tool, fixture or workpiece. When the original accuracy of machine tools, tools, fixtures, and workpiece blanks all meet the process requirements without considering dynamic factors, the influence of adjustment errors will play a decisive role in machining accuracy.

9. Measurement error.

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