How to Determine the Accuracy of a Machining Center?

The accuracy of a machining center is crucial because it affects the machining quality. So how to determine the accuracy of a machining center? Let's talk about it from four aspects.

1. Positioning of vertical machining center specimens:

The test piece should be located in the middle of the X stroke and placed along the Y and Z axes at an appropriate position suitable for the positioning of the test piece and fixture, as well as the length of the tool. When there are special requirements for the positioning position of the specimen, it should be specified in the agreement between the manufacturer and the user.

2. Fixation of test piece:

The test piece should be easily installed on a dedicated fixture to achieve maximum stability of the tool and fixture. The installation surface of the fixture and specimen should be straight.

The parallelism between the installation surface of the specimen and the clamping surface of the fixture should be checked. Suitable clamping methods should be used to allow the tool to penetrate and machine the entire length of the center hole. It is recommended to use countersunk screws to fix the specimen to avoid interference between the tool and the screw, or other equivalent methods can be used. The total height of the specimen depends on the chosen fixing method.

3. Materials, cutting tools, and cutting parameters of the test piece:

The material, cutting tool, and cutting parameters of the test piece should be selected according to the agreement between the manufacturer and the user, and should be recorded. The recommended cutting parameters are as follows:

1) Cutting speed: about 50m/min for cast iron parts; Aluminum parts are approximately 300m/min.

2) Feed rate: approximately (0.05~0.10) mm/tooth.

3) Cutting depth: All milling processes should have a radial cutting depth of 0.2mm.

4. Size of test piece:

If the specimen has been cut several times, resulting in a decrease in external dimensions and an increase in aperture, when used for acceptance inspection, it is recommended to choose the final contour machined specimen size that is consistent with the specified dimensions in this standard, in order to accurately reflect the cutting accuracy of the machining center. The test piece can be repeatedly used in cutting tests, and its specifications should be maintained within ± 10% of the characteristic dimensions given in this standard. When the specimen is reused, a thin layer cutting should be performed before conducting a new precision cutting test to clean all surfaces before conducting the test.

I estimate that everyone will encounter another problem when using a machining center. Why does the accuracy of the machining center deteriorate when used? Did we buy counterfeit goods?

The poor machining accuracy of the parts in the machining center is generally due to the feed dynamics between the axes not being adjusted according to the error during installation and adjustment, or due to changes in the transmission chain of the machine tool's axes after wear and tear (such as changes in screw clearance, pitch error, axial displacement, etc.). It can be resolved by readjusting and modifying the gap compensation amount.

When the dynamic tracking error is too large and an alarm is triggered, it can be checked whether the servo motor speed is too high; Whether the position detection component is in good condition; Is the position feedback cable connector in good contact; Whether the corresponding analog output latch and gain potentiometer are in good condition; Is the corresponding servo drive device functioning properly.

If overshoot during machine tool movement causes poor machining accuracy, it may be due to short acceleration and deceleration times. The speed change time can be appropriately extended; It is also possible that the connection between the servo motor and the screw is loose or the rigidity is too poor, and the gain of the position ring can be appropriately reduced. It may be due to the roundness exceeding the tolerance when the two axes are linked, and this deformation may be caused by mechanical failure to adjust properly. Poor positioning accuracy of the shaft or improper compensation of the screw clearance can lead to roundness errors when exceeding the limit.