There are many factors that affect the machining accuracy of parts, among which the accuracy of machine tool is one of the main factors. After long-term use or major repair of the machine tool, all important accuracy indicators should be checked and tested. Geometric accuracy is one of the accuracy of machine tools, which refers to the mutual position accuracy of various components and the shape and position accuracy of main parts when the machine tool is running. The geometric accuracy test of machine tools is a static test under non working conditions.
Geometric accuracy test of common milling machines
1. Precision inspection of milling machine workbench
(1) Inspection of flatness of worktable. Make the workbench in the middle of the longitudinal and transverse travel, place two gauge blocks with equal height on the workbench table in all directions, put a test ruler on the two gauge blocks, and then use a feeler gauge and gauge block to test the distance between the workbench table and the ruler.
(2) Verticality inspection of the longitudinal and transverse movement of the workbench. Place the 90 degree ruler in the middle of the workbench, make one inspection surface of the 90 degree ruler parallel to the horizontal (or longitudinal) direction, move the workbench longitudinally (or horizontally), and use a dial indicator to inspect on the other inspection surface of the 90 degree ruler. The maximum difference between the readings of the dial indicator is the perpendicularity error. During inspection, the lifting table should be locked.
(3) The parallelism inspection of the worktable top by the longitudinal movement of the worktable. Make the worktable in the middle of the horizontal stroke. On the worktable top, cross the center, place two gauge blocks with equal height in the T-shaped groove, place the inspection ruler on it, push the dial indicator contact on the inspection surface of the ruler, and move the worktable longitudinally for inspection. The maximum difference between the readings of the dial indicator is the parallelism error. During inspection, the traverse feed and lifting table should be locked.
(4) The parallelism of the worktable top is tested by the horizontal movement of the worktable. Place two gauge blocks with the same height in the middle of the worktable and parallel to the horizontal moving direction of the worktable, place the inspection ruler on it, place the dial indicator contact in the center of the spindle, and make it top on the inspection surface of the ruler, and move the worktable horizontally for inspection. The maximum difference between the readings of the dial indicator is the parallelism error. During inspection, the lifting table should be locked.
(5) The parallelism test of the T-shaped groove in the center of the workbench facing the longitudinal movement of the workbench. Make the workbench in the middle of the horizontal stroke, push the dial indicator contact against the inspection surface of the special slider close to the side of the central T-shaped groove, and move the workbench longitudinally for inspection. The maximum difference between the readings of the dial indicator is the parallelism error. Both sides of the central T-groove shall be inspected. During inspection, the traverse feed and lifting table should be locked.
2. Precision inspection of milling machine spindle
(1) Axial runout inspection of spindle. Push the dial indicator contact against the center of the end face of the special inspection rod inserted into the taper hole of the spindle, and rotate the spindle for inspection. The maximum difference between the readings of the dial indicator is the error of axial jump.
The axial runout tolerance of the spindle of common milling machines is 0.01mm. The axial jump error is too large, which will produce large vibration and inaccurate size control during processing, as well as the phenomenon of tool dragging.
The axial jump error is too large. If it is caused by too tight or loose adjustment of the bearing, the specified requirements can be achieved by adjusting the tightness of the bearing; If it is caused by the wear of the main shaft, the main shaft needs to be replaced.
(2) Runout inspection of bearing surface of spindle shoulder. The end face circular runout tolerance of the bearing surface of the spindle shoulder of common milling machines is 0.02mm. If the end face circular runout error of the bearing surface of the shaft shoulder is too large, it will cause the end face circular runout of the milling cutter positioned and installed with the shaft shoulder of the spindle, affect the dimensional accuracy and surface roughness of the parts, accelerate the wear of the milling cutter due to uneven wear of the cutter teeth, and reduce the service life of the milling cutter. The solution to the excessive runout error of the bearing surface of the shaft shoulder is the same as the solution to the excessive axial runout error of the main shaft.
(3) Horizontal milling machine spindle rotation axis to the table surface parallelism inspection. The parallelism tolerance of the spindle rotation axis of common milling machines to the worktable surface is 0.03mm, and the protruding end of the inspection rod is only allowed to tilt downward. If the parallelism error is too large, it will affect the parallelism of the machined surface of the part. If the transverse secondary feed is made, obvious tool joint marks will be produced. If the parallelism error exceeds the tolerance, adjust the bearing to meet the specified requirements.