(1). Figure 1-a shows the arrangement of one end fixed and one end suspended. This type of installation has low load carrying capacity and low axial stiffness and is only suitable for short lead screws, such as the adjustment of CNC machine tools or the vertical coordinates of lifting CNC milling machines.
(2). Figure 1-b shows the arrangement of one end fixed and one end supported. This type of installation is mostly used in the case where the lead screw is long and the rotation speed is high. When the force is large, the number of angular contact ball bearings must be increased. When the rotation speed is not high, the more economical thrust ball bearing is used instead of the angular contact ball bearing.
(3). Figures 1-c and 1-d show the arrangement of the two ends fixed. In this arrangement, the screw pair has the best support rigidity, and the lead screw is pre-stretched by the pre-tightening force of the bearing to reduce the influence of the thermal deformation of the screw. This method is often used when the length of the screw is not large, but the design should pay attention to improve the bearing capacity, support stiffness and pre-tension of the screw assembly, otherwise it will affect the bearing life, and also because of the pre- Adding load is not easy to control and increases the additional torque of the motor.
2) Machine guide rails Most of the common lathe guide rails use sliding guide rails, which have large dynamic and static friction coefficients. They will have different degrees of wear after a period of use, which will have a great impact on the accuracy and maintainability of the machine tool. Therefore, in order to carry out numerical control transformation, it is necessary to carry out necessary maintenance treatment for the condition of the machine guide rail. For the more serious wear, it is necessary to carry out overhaul, that is, grinding, quenching, plasticizing, shaving, etc., while adopting reasonable Lubrication, fully guarantee its accuracy.
3), the connection between the motor and the screw is on the premise of meeting the requirements of the machine tool. In order to reduce the transmission error caused by the intermediate link, we will directly connect the motor and the lead screw through the coupling, which depends on the actual situation in the transformation. set. Generally for small lathes such as C6116, due to limited space, especially the X-axis, the motor and the screw pair can not be directly connected, and the gear pair or synchronous belt is used for transmission. For large lathes such as C6150, the bed is 5 meters long. Since the lead screw is long and the diameter is large, in addition to the problem of the transmission force, the low speed performance and the acceleration/deceleration inertia matching problem must be considered. The motor is often driven by several stages of deceleration. Whether using gear or synchronous belt drive, the elimination of the transmission clearance is more critical. Commonly used methods in gear transmission include the wrong tooth backlash method, the eccentric shaft adjustment method, etc. In the synchronous belt theory transmission, the adjustment center distance or the tension wheel anti-backlash method is often used.
2, the transformation of the spindle part of the lathe spindle to drive the workpiece to rotate at different speeds is the main movement in the turning process, consuming most of the power of the machine. The ordinary lathe is driven by the main motor via the belt, and the spindle is rotated by the main shaft gearbox. The main shaft box is obtained by manual or automatic shifting (9~24) speed, and the shifting and reversing of the main shaft are controlled by electromagnetic or hydraulic clutch; and the CNC lathe spindle The box consists of an electric spindle or a conventional mechanical spindle unit plus a variable frequency motor and a frequency converter. In the case of numerical control, the ordinary lathe retains the original headstock in most cases without modification or minor changes. If you need to change, you should pay attention to the following points:
If the original spindle contains the shifting, reversing and lubricating functions of the hydraulically operated spindle, it is necessary to install a separate ordinary motor to prevent the hydraulic system from being malfunctioned by the main motor being reversed or the speed is changed.
If the original mechanical shifting gear is not required, the gear set in the headstock should be fixed on a constant speed chain, and the friction plates should also be welded to avoid accidents due to misoperation.
Whether the machine tool can be threaded is another important part of the numerical control transformation of the spindle part. The traditional lathe is often processed by the hanging wheel set. The different threads need different hanging wheel sets, which is very troublesome to operate. As shown in Figure 2, we usually add a photoelectric encoder at the end of the spindle or at the hanging wheel frame. The rotation speed is the same as the spindle speed. The spindle rotates once, the photoelectric code wheel rotates one turn, and the feed axis is controlled by feedback to the system. Synchronization of the spindle to machine the thread with the desired pitch. According to the different coding methods, the photoelectric code disc can be divided into an incremental photoelectric code disk and an absolute photoelectric code disk. At present, the domestically used incremental photoelectric code disk. According to the number of lines on the photoelectric code disc, it can be divided into 1024 lines, 2048 lines, etc., we usually use 1024 lines to meet the requirements.
Figure 2 Spindle encoder installation diagram
3. Modification of the tool holder part At present, the CNC lathe tool holder is basically an electric tool holder, which is characterized by more accurate and rapid positioning. Old-fashioned traditional lathe tool holders are mostly manual, hydraulic or a small part of the electric, which can be replaced as needed.
The electric knife holder can be divided into a horizontal turret tool holder (generally 8 to 12 knives are installed) and a vertical electric knife holder. The vertical electric turret has four stations (or six stations), each of which is provided. There are also points for lifting the knife holder (the both ends of the toothed disc) and the lifting-free knife holder (the three-ended toothed disc). The horizontal turret tool holder is relatively expensive, and the vertical four-station electric knife holder is often used in the transformation.
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