1. Machine tool system error

The errors in manufacturing, installation and debugging of machine tools and wear during use will directly affect the accuracy of CNC machining. Among them, there are mainly spindle rotation error, straight line error of guide rail and transmission system error.

(1) The rotation error of the spindle, the spindle of the machine tool is the reference for installing the tool or positioning the part, and the size of the error will directly affect the machining accuracy of the part. Its rotation error can be decomposed into three basic forms: radial circle runout, axial circle runout, and inclination swing.

(2) The error of the guide rail, the machine tool guide rail is the basis of the formation of motion during the processing process, and the size of the error will affect the benchmark of the processing movement. Machine tool guide rail errors include: straight line error of guide rail and parallel error of guide rail.

(3) Transmission chain error, due to the error, assembly error and wear of each component in the transmission chain, resulting in the cumulative error of the entire transmission chain.

2. Tool parameter error

For different types of tools, the degree to which tool parameters influence machining errors varies. Since the size and shape accuracy of each tool are different, the corresponding cutting data (speed, back knife volume, cutting speed) must be formulated.

3. Workpiece positioning error

Workpiece positioning error is the processing error caused by the inaccurate positioning of the machined part on the fixture. The main cause is the error caused by the non-overlap of the reference, because the positioning reference during workpiece processing does not coincide with the design reference and process reference on the part drawing at the time of product design. Positioning the copy body accuracy also introduces errors into the machining. These references do not coincide with errors. Under the action of the machining load, it will be introduced into the workpiece accuracy.

4. Error caused by force deformation of the process system

(1) The influence of workpiece stiffness. In the whole processing process system, under the action of cutting force, the deformation of the workpiece will affect the machining accuracy.

(2) The influence of tool stiffness. In the machining process, different tools show different stiffness, and the error of tools with large stiffness has little effect, so try to choose a tool with high rigidity.

(3) The influence of the stiffness of machine tool components. There are many components of the machine tool, and the calculation of its stiffness is complicated, so far it can only be determined experimentally. Under the action of machining load, the deformation of machine tool components is non-linear and has unloading hysteresis. The unloading hysteresis phenomenon is that when the load disappears, the unloading curve does not coincide with the loading curve, but lags behind the loading curve, and the area contained by the two lines is the thermal energy generated by friction and contact deformation. The first unloading deformation cannot recover from the loading starting point, indicating the existence of residual deformation, but after repeated loading and unloading repeatedly, the starting point of the loading curve and the unloading curve will gradually coincide, and the residual deformation will be reduced to zero.