What are the main reasons for machining errors of mechanical parts?

Machining accuracy refers to the degree of conformity between the actual geometric parameters (size, shape and position) of the mechanical parts after machining and the ideal geometric parameters. In the machining of mechanical parts, the error is inevitable, but the error must be within the allowable range. Through the error Analyze and master the basic laws of its changes, so as to take corresponding measures to reduce machining errors and improve machining accuracy.

1. Spindle rotation error. 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 spindle are: the coaxiality error of several journals of the spindle, the bearing Various errors in itself, coaxiality error between bearings, spindle deflection, etc.

2. Guide rail error. The guide rail is the benchmark for determining the relative positional relationship of each machine tool component on the machine tool, and it is also 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. Transmission chain error. The transmission error of the transmission chain refers to the error of the relative motion between the transmission elements at the beginning and the end of the transmission chain. caused by wear and tear.

4. The geometric error of the tool. Any tool will inevitably wear during the cutting process, which will cause changes in the size and shape of the workpiece.

5. Positioning error. One is the reference misalignment error. The reference used to determine the size and position of a surface on the part drawing is called the design reference. It is used on the process drawing to determine the size of the machined surface in this process. , The datum on which the position is based is called the process datum. When machining the workpiece on the machine tool, it is necessary to select several geometric elements on the workpiece as the positioning datum during processing. If the selected positioning datum does not coincide with the design datum, a datum will be generated. Misalignment error. The second is the inaccurate manufacturing error of the positioning pair.

6. The error caused by the force deformation of the process system. One is the stiffness of the workpiece. If the stiffness of the workpiece in the process system is relatively low compared to the machine tool, tool, and fixture, under the action of the cutting force, the deformation of the workpiece due to insufficient stiffness will affect the workpiece. The influence of machining accuracy is relatively large. The second is the stiffness of the tool. The rigidity of the cylindrical turning tool in the normal direction of the machined surface is very large, and its deformation can be ignored. When boring an inner hole with a small diameter, the stiffness of the tool bar is very poor, and the tool The deformation of the rod has a great influence on the machining accuracy of the hole. The third is the rigidity of the machine tool parts. The machine tool parts are composed of many parts. There is no suitable simple calculation method for the rigidity of the machine tool parts. At present, the experimental method is mainly used to determine the rigidity of the machine tool parts.

7. Error 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 machining, the machining error caused by thermal deformation can sometimes account for 50% of the total workpiece error .

8. Adjustment error. In each process of machining, the process system must always be adjusted in one way or another. Since the adjustment cannot be absolutely accurate, adjustment errors occur. In the process system, the workpiece and the tool are in the machine tool. The mutual position accuracy of the machine tool is guaranteed by adjusting the machine tool, tool, fixture or workpiece. When the original precision of the machine tool, tool, fixture and workpiece blank meets the process requirements without considering dynamic factors, the influence of adjustment error , plays a decisive role in the machining accuracy.

9. Measurement error. When the mechanical parts are processed or measured 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.