The main causes of CNC precision machining errors

The main causes of CNC precision machining errors

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

1. Spindle rotation error.
   The spindle rotation error refers to the change of the spindle\’s actual rotation axis relative to its average rotation axis at each moment. The main causes of spindle radial rotation errors include: coaxiality errors in several sections of the spindle journal, various errors in the bearing itself, coaxiality errors between bearings, spindle deflection, etc.
2. Guide rail error.
   The guide rail is the benchmark for determining the relative positional relationship of various machine tool components on the machine tool, and is also the benchmark for machine tool movement. Uneven wear and installation quality of guide rails are also important factors causing guide rail errors.
3. Drive chain error.
   The transmission error of the transmission chain refers to the error in the relative motion between the transmission elements at the beginning and end of the transmission chain. Transmission errors are caused by manufacturing and assembly errors of various components of the transmission chain and wear during use.
4. Geometric error of the tool.
   During the cutting process of any tool, wear will inevitably occur, causing 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 location of a surface on a part drawing is called a design datum. The reference objects on the process drawing used to determine the size and position of the processing surface of the process are called process reference objects. When processing a workpiece on a machine tool, several geometric elements on the workpiece must be selected as the positioning datum during processing. If the selected positioning datum does not coincide with the design datum, a datum misalignment error will occur. Second, the manufacturing error of the positioning pair is inaccurate.
6. Errors caused by stress and deformation 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 tool stiffness. The rigidity of the cylindrical turning tool in the normal direction of the processing surface is very large, and its deformation is negligible. When boring a small-diameter inner hole, the rigidity of the tool holder is very poor, and the force and deformation of the tool holder have a great impact on the machining accuracy of the hole. The third is the stiffness of machine tool components. Machine tool components are composed of many parts. To date, there is no suitable simple calculation method for the stiffness of machine tool components. Currently, experimental methods are mainly used to determine the stiffness of machine tool components.
7. Errors caused by thermal deformation of the process system.
   Thermal deformation of the process system has a greater impact on machining accuracy. Especially in precision machining and large parts processing, the machining error caused by thermal deformation can sometimes account for 50% of the total error of the workpiece.
8. Adjustment errors.
   In every process of machining, the process system must be adjusted in one way or another. Since adjustments cannot be absolutely accurate, adjustment errors can occur. In the process system, the mutual position accuracy of the workpiece and the tool on the machine tool is ensured by adjusting the machine tool, tool, fixture or workpiece. When the original accuracy of machine tools, cutting tools, fixtures, and workpiece blanks all meet process requirements without considering dynamic factors, the impact of adjustment errors will play a decisive role in machining accuracy.
9. Measurement error.
   When measuring parts during or after machining, measurement accuracy is directly affected by the measurement method, measuring tool accuracy, workpiece, and subjective and objective factors.

The main causes of CNC precision machining errors are as above. If you want to know more about CNC precision machining, please contact us.