Main causes of cnc precision machining errors
Cnc machining accuracy refers to the degree of conformity between the actual geometric parameters (size, shape and position) and the ideal geometric parameters. In processing, error is inevitable, but the error must be within the allowable range. Through error analysis, grasp the basic law of its change, so as to take corresponding measures to reduce machining errors and improve machining accuracy.
Then there are also reasons for errors, which are roughly as follows:
1. Spindle rotation error_
Spindle rotation error refers to the change of actual spindle rotation axis 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, coaxiality error between bearings, and the deflection of the main shaft.
Cnc precision machining of aluminum parts
2. Guide rail error. __
The guide rail is the benchmark for determining the relative position of various machine tool parts on the machine tool, and 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. Drive chain error_
The transmission error of the transmission chain refers to the relative motion error between the transmission components at the head and tail of the transmission chain. The transmission error is caused by the manufacturing and assembly errors of the components of the transmission chain and the wear in the use process.
4. Geometric error of tools.
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.
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 design datum. The reference object on the process drawing used to determine the size and position of the processing surface of the process 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 for machining. If the selected positioning datum does not coincide with the design datum, datum misalignment error will occur. Second, the manufacturing error of positioning pair is inaccurate.
6. Errors caused by force and deformation of process system.
The first is the rigidity of the workpiece. In the process system, if the rigidity of the workpiece is relatively low compared with that of the machine tool, tool and fixture, the workpiece deformation due to insufficient rigidity will have a greater impact on the machining accuracy under the action of the 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. When boring a small diameter inner hole, the rigidity of the cutter bar is very poor. The force and deformation of the cutter bar 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 process system.
The thermal deformation of the process system has a great influence on the machining accuracy, especially in precision machining and large part machining, the machining error caused by thermal deformation can sometimes account for 50% of the total error of the workpiece.
8. Adjustment error.
In each process of machining, the process system must be adjusted in one way or another. Adjustment errors occur because the adjustment cannot be absolutely accurate. In the process system, the mutual position accuracy of workpiece and cutter on the machine tool is guaranteed by adjusting the machine tool, cutter, fixture or workpiece. When the original accuracy of machine tool, cutter, fixture and workpiece blank meets the process requirements without considering dynamic factors, the influence of adjustment error will play a decisive role in the processing accuracy.
9. Measurement error.
When measuring parts during or after processing, the measurement accuracy is directly affected by the measurement method, measuring tool accuracy, workpiece and subjective and objective factors.