In the machining industry, the size of the machining error reflects the machining accuracy. Machining centers are high-precision machining equipment, but machining errors are unavoidable. The reasons for common errors in machining centers are as follows.

Errors in the machining center equipment itself

This kind of error exists objectively, mainly including spindle rotation error, guide rail error and transmission chain error. As one of the most important components in the machining process, the spindle directly affects the accuracy of the machining workpiece. The guide rail is the benchmark for determining the relative positional relationship of the components on the machining center, and it is also the benchmark for the processing movement. The manufacturing error of the guide rail itself, the uneven wear of the guide rail and the installation quality are important factors that cause the guide rail error. Drive chain errors are caused by wear and tear during use.

Geometric errors in the machining process

The geometric error includes the geometric error of the tool and the geometric error of the fixture. Any tool will inevitably wear during the cutting process, which will cause changes in the size and shape of the workpiece. The function of the fixture is to make the workpiece equivalent to the tool and the machine tool to have the correct position, so the geometric error of the fixture has a great influence on the machining error (especially the position error).

Positioning error

The positioning error mainly includes the reference misalignment error and the inaccurate manufacturing error of the positioning pair. In the process of workpiece processing, several geometric elements on the workpiece must be selected as the positioning reference during processing. If the selected positioning datum does not coincide with the design datum, a datum misalignment error will occur.

Adjustment error

In each process of the CNC machining center, the process system must be adjusted in one way or another. Since the adjustment cannot be absolutely accurate, an adjustment error occurs. In the processing system, the mutual positional accuracy of the workpiece and the tool on the machine tool is guaranteed by adjusting the machine tool, tool, fixture or workpiece.

Accuracy is an important parameter of CNC machining centers. Only by understanding the causes of errors can we reasonably avoid accuracy errors in the reprocessing process, thereby improving the quality of orders and ensuring the pass rate.

Pay attention during processing:

• When forming high-precision workpieces, use a dial indicator to detect the tool on the spindle, so that the static runout is controlled within 3µm, and the tool holder system needs to be re-installed or replaced if necessary.

• Whether it is a part processed for the first time or a part that is repeatedly processed periodically, check and check the program one by one and one by one according to the drawing process, program and tool adjustment card, especially for the tool length compensation and radius compensation in the program, and try again if necessary.

• During trial cutting and feeding, when the tool runs to 30~50mm on the workpiece surface, it must be kept in low-speed feed to verify whether the remaining coordinate values of the coordinate axes and the coordinate values of the X and Y axes are consistent with the pattern.

• For some knives with test requirements, the "progressive" method is adopted. For example, when boring a hole, it can be modified from large to small while trying to trim it.

Conclusion