How to judge the accuracy of a machining center?

Everyone's workshop is estimated to have a machining center, a machining center accuracy is crucial, because the accuracy of the machining center affects the quality of processing, so about the accuracy of the machining center, engaged in machining has also been studying ways to reduce errors as much as possible. So how to judge the accuracy of a machining center?

01 Vertical machining center test piece positioning

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

02 Fixing of specimen

The specimen should be easily mounted on a special fixture to achieve maximum stability of the tool and fixture. The mounting surface of the fixture and the specimen shall be flat and straight.

The parallelism between the mounting surface of the specimen and the clamping surface of the fixture shall be checked. A suitable clamping method should be used to allow the tool to penetrate and machine the full length of the center hole. It is recommended to use countersunk screws to hold the specimen in order to avoid interference between the tool and the screws, or other equivalent methods can be used. The total height of the specimen depends on the chosen fixing method.

03 Material, tool and cutting parameters of the specimen

The material of the test piece and the cutting tool and cutting parameters are 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; about 300m/min for aluminum parts.

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

(3) depth of cut: all milling processes in the radial depth of cut should be 0.2mm.

04 Size of the test piece

If the test piece is cut several times, the shape size is reduced and the hole diameter is increased, when used for acceptance inspection, it is recommended to choose the final contour machining test piece size is consistent with that specified in this standard, in order to truthfully reflect the cutting accuracy of the machining center. The test piece can be used repeatedly in the cutting test, its specifications should be maintained within 10% of the characteristic size cab given in this standard. When the test piece is used again, a thin cut should be made to clean up all the surfaces before conducting a new fine cutting test.

It is estimated that we will encounter another problem in the process of using the machining center, why the machining center with the use of the accuracy will become worse? Did we buy a parallel product?

Machining center parts of poor machining accuracy is generally due to the installation and adjustment, the feed dynamic between the axes according to the error is not adjusted, or due to the use of wear and tear, the machine tool shaft drive chain has changed (such as screw clearance, pitch error changes, axial runout, etc.). Can be readjusted and modify the amount of gap compensation to solve.

When the dynamic tracking error is too large and alarm, check: servo motor speed is too high; position detection components are good; position feedback cable connectors are in good contact; the corresponding analog output latch, gain potentiometer is good; the corresponding servo drive device is normal.

If the processing accuracy is not good due to overshoot when the machine is in motion, it may be that the acceleration and deceleration time is too short, and the speed change time can be extended appropriately; it may also be that the connection between the servo motor and the screw is loose or too rigid, and the gain of the position ring can be reduced appropriately, and it may be that the roundness of the two axes in linkage is too poor, and this deformation may be caused by the machinery not being adjusted properly. Bad positioning accuracy of the axis or improper compensation of the screw gap can lead to roundness error when over quadrant.

However, there is another saying in the folklore: high precision is guaranteed by people. It is said that the world's most accurate machine tools are calibrated by people, in Japan there are dedicated to such staff to calibrate the machining accuracy of machine tools, such people in each machine tool manufacturer is invaluable. According to this theory, it is possible to assemble a machine with amazing machining accuracy by using relatively less accurate parts.