The Main motion requirements of CNC lathe machining:
- The spindle speed is continuously adjustable within a certain
range.
- The spindle has enough drive power.
- The spindle component has high rotation accuracy and stable
operation.
- The main shaft components have sufficiently high rigidity and
shock resistance.
The main transmission system of economical CNC lathes is almost identical to the basic structure of ordinary lathes, that is, gear transmission is mainly adopted. In order to meet the requirements of automatic transmission of CNC lathes in machining, electromagnetic clutch transmission or two-speed motor transmission is generally used in transmission. There are also some economical CNC lathes that use handle forks for manual transmission. Economical CNC lathes generally have 4-8 speeds, which are somewhat lacking for high-level automatic machining, but they can meet general machining requirements.
The main drive system of the standard CNC lathe adopts a DC or AC stepless speed regulation spindle motor, which is driven to the spindle box through a belt to drive the spindle to rotate, thereby realizing automatic stepless speed regulation and constant speed cutting control. In order to increase the speed regulation range and ensure that the speed of the spindle motor is not too low, sometimes two sets of gears are set in the spindle box, and the spindle speed range is divided into high speed and low speed. Use hydraulic cylinders to push sliding gears to achieve gear shifting, or use electromagnetic clutches to switch on or off power transmission.
The spindle speed change of the standard CNC lathe is automatically carried out in accordance with the instructions of the machining program. In order to ensure the accuracy of the main drive of the lathe, reduce noise and vibration, the main drive chain should be as short as possible; in order to meet the requirements of different machining techniques and obtain the best cutting speed, the main drive system should be able to steplessly change in a wide range ; In order to ensure the productivity and machining quality of the turning end face, constant cutting speed control should also be achieved. In addition, on a full-function CNC lathe, the spindle should be able to cooperate with other components to realize automatic clamping of the workpiece.
The pulse signal generator used in the spindle movement mainly has two types: photoelectric and electromagnetic. The spindle encoder on the CNC lathe adopts a photoelectric pulse generator synchronized with the spindle. The pulse signal generator can be synchronized through a 1:1 belt drive installed on the intermediate shaft, or synchronized through a pair of gears, or coaxially installed with the main shaft through a flexible coupling. On high-level CNC lathes (turning centers), the control of the C axis (that is, the axis of rotation around the main shaft) must be realized.
The main
transmission system of the turning center is basically the same as the general
CNC lathe, except that the C axis coordinate function of the spindle is added
to realize the spindle oriented parking and circular feed, and realize the
linkage interpolation of the C axis and the Z axis under the control of the CNC
device , Or C-axis and X-axis linkage interpolation. In this way, drilling,
milling, threading and surface machining can be performed on any part of the
cylindrical surface or end surface of the revolving body. The rotation (ie,
feed) or indexing movement of the C-axis is realized by the C-axis servo motor
through a precision worm pair or slip gear pair, and an indexing gear.
