What are the main factors that affect the accuracy of the CNC machines ?

- Dec 13, 2019-

After repeated exploration of the accuracy of the machine tool, it was found that the most important factor affecting the accuracy of the machine tool is not the wear of the transmission chain (of course, this is also one of the influential factors, but the cost of repair is extremely high), but the wear of the machine's cradle bearing problem.

When the Y2250 machine tool's cradle bearing wears severely, it will cause the axial movement and vibration of the cradle, which will cause the ring gear of the gear to pulsate radially and cause the surface roughness of the gear surface to be large.

There are two main reasons for the wear of Y2250 machine shaker bearings. One is that the lubrication system of the machine tool is not designed, the lubricant is too little, and it is not easy to check when the oil is lost (especially the rear bearing); the second is the resistance of domestic castings. Abrasiveness is not good.


For the wear of Y2250 machine tool cradle bearings, repair is easier and the cost is lower. The method is to polish the outer circle of the cradle and the inner hole of the bearing seat with a vertical lathe. The actual size of the hole D1 is then used as a bearing roller. The outer diameter of the roller is d0 = (D1-d1) /2+0-0.01-0.02mm, and the size consistency of each roller is better.

After repairing the Y2250 machine using this method, the ring gear runout of the large wheel was increased from 0.09 mm to 0.17 mm to 0.04 mm to 0.08 mm. (This data is measured when the tool runout is 0.03 mm in the radial direction and 0.02 mm in the axial direction. ).


After the machine tool is repaired, the following adjustments and inspections must be held on the machine tool: ① Adjust the clearance between the spindle of the cutter head and make the spindle runout at about 0.01 mm. ② Adjust the clearance between the main shaft of the workpiece and make the radial and axial runout of the main shaft between 0.006 mm and 0.01 mm. ③ The clearance between the worm wheel and the worm of the adjusting shaker is between 0.02 mm and 0.05 mm. ④ The clearance between the main shaft worm gear and the worm of the adjusted workpiece is between 0.01 mm and 0.03 mm. ⑤ Check and adjust the coordination of gears and keys on each drive shaft. ⑥ Check whether there is serious wear or damage in other parts.


2 Incisive tooth process

Gear cutting technology includes tooling design and manufacturing accuracy, operating gear cutting sequence, operating specifications, and precision cutting allowance.

2.1 Design and manufacturing accuracy of cutting gear

2.1.1 Large round tooling

For manufacturers who do not have the conditions to manufacture spring disc clamps, two methods of large wheel tooling can be used. If it is a large-volume product, it is best to use the overall fixture. This can ensure that the manufacturing quality of the fixture is: 0.01 mm radial, 0.005 mm axial, that is, after installing the machine tool, the radial runout is about 0.015 mm, axial The runout is about 0.008 mm.

For multi-variety, low-volume products, split fixtures should be used because it is convenient to reduce the cost of tooling. The tooling of this structure is measured on a gear milling machine with a radial runout of about 0.03 mm and an axial 0.02 mm to 0.03 mm.


2.1.2 Small round tooling

After repeated research on the original design of the small round tooling, it was found that there is a place that can be improved, that is, the screw hole of the front cone of the small wheel tooling has been changed from 2-M12 to uniformly distributed 4-M12. When correcting the tool runout, use the M12 ejector screw to fine-tune the tool runout.

Generally speaking, the small round tooling can only be aligned to the runout of 0.015 mm to 0.03 mm by using the padding method, and the ejection screw can be adjusted to the runout of 0.005 mm to 0.01 mm. The runout values are all adjusted by using a proof rod. Measured in the middle of the face, this is faster than using the padding method, and the accuracy is high.

At the same time, the large wheel and small wheel tooling (including the elastic sleeve) are all carburized and quenched with 20CrMnTi data to improve the application life of the tooling.


For more details, welcome to check our website: www.lemo-machining.com

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