How many reasons do you know that affect the accuracy of turning and milling?

There are many factors that affect the machining accuracy of a turning-milling compound machine tool, such as geometric errors, thermal errors, force errors, and random errors. Among them, geometric errors have a greater impact on the machining accuracy, usually reaching more than 40% of the total error, and there are some other Factors, let’s understand.

　　 1. Rotation accuracy of electric spindle system

　　The CNC turning-milling compound machining center is a high-precision machining machine tool. The spindle group is a key component. The rotation accuracy of the spindle group directly affects the accuracy of the processed workpiece.

　　 In order to ensure the high rotation accuracy of the spindle group, in the electric spindle system, the connection between the spindle and the motor rotor, the coordination between the stator jacket and the spindle box, and the coordination between the two ends of the spindle and the bearing group, etc. adopt the following series Process measures:

　　(1) Before assembling the electric spindle, ensure the accuracy of the spindle box hole. The roundness of the hole, the dimensional tolerance, and the coaxiality of the front and rear bearing holes are all within the required range;

　　(2) Grind the spindle box hole according to the size of the bearing outer ring during assembly.

　　 After taking the above measures, the rotation accuracy of the electro-spindle system is guaranteed. The radial runout and end runout of the spindle are within 0.002mm, which lays a foundation for ensuring the machining accuracy of the workpiece.

　　 2. The indexing accuracy and exact stop accuracy of the electric spindle

　　 In order to achieve high indexing accuracy and accurate stop accuracy of the electric spindle system, a built-in spindle motor (electric spindle for short) is adopted, and the spindle and the motor rotor are assembled into one body to reduce the influence of the intermediate transmission link on the accuracy of the spindle. When working, the rotation of the motor rotor drives the main shaft to rotate.

　　 In order to achieve the above purpose, the following solutions are adopted:

　　(1) The motor rotor and the machine tool spindle adopt a special assembly process to ensure the rigidity of the connection between the machine tool spindle and the inner hole of the motor rotor, and can transmit large cutting torque.

　　(2) A higher level of high-speed dynamic balance is adopted when the electric spindle group is assembled, which reduces the residual imbalance of the spindle group and ensures the stability of the spindle during high-speed rotation.

　　(3) The electric spindle system adopts the spindle brake and damping device. When the spindle needs to be stopped for milling or drilling, the spindle is in a brake state to ensure that the spindle does not shake during milling.

　　 Three, the thermal balance of the electric spindle system

　　The motor in the electric spindle system is a heating element, and the front and rear bearings of high-speed rotation are also heating elements, which will increase the temperature of the electric spindle and affect the machining accuracy of the turning-milling compound. How to eliminate the influence of the heat source on the accuracy of the machine tool spindle and realize the thermal balance of the electric spindle system is a key problem to be solved in the design and manufacturing process of the turning-milling composite machining machine tool. To this end, the following measures have been taken:

　　(1) The spindle box adopts a thermally symmetrical design. The heat dissipation ribs outside the box body are symmetrically distributed on both sides, so that the heat generated by the spindle box is dissipated through the heat dissipation ribs as soon as possible. At the same time, because the heat dissipation ribs are symmetrically distributed, the spindle The axis will not be offset.

　　(2) The preload and lubrication conditions of the spindle bearing are controlled according to the design requirements.

　　(3) Adopt external circulation cooling measures for the main heat source of the motor.

　　 Through the above analysis, it can be known that in the manufacturing and assembling process of the turning and milling compound processing machine tool, as long as the rotation accuracy, indexing accuracy and accurate stopping accuracy of the electric spindle system are reasonably solved, the turning and milling compound processing machine tool can be used. It has high machining accuracy and accuracy retention.