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1.CNC lathe bed structure
CNC lathes are also composed of spindle boxes, tool holders, feed transmission systems, bed bodies, hydraulic systems, cooling systems, lubrication systems, etc., but the feed systems of CNC lathes and horizontal lathes are essentially different in structure. The movement of the spindle of a horizontal lathe is transmitted to the tool holder through the hanging wheel frame, feed box, and slide box to achieve longitudinal and lateral feed movement. CNC lathes use servo motors, which are transmitted to the slide and tool holder through ball screws to achieve Z-direction (longitudinal) and A-direction (lateral) feed movement. CNC lathes also have the function of processing various threads, and the movement relationship between the spindle rotation and the tool holder movement is controlled by the CNC system. A pulse encoder is installed in the spindle box of the CNC lathe, and the movement of the spindle is transmitted to the pulse encoder 1:1 through a synchronous toothed belt. When the spindle rotates, the pulse encoder sends a detection pulse signal to the CNC system, so that the rotation of the spindle motor and the cutting feed of the tool holder maintain the motion relationship required for thread processing, that is, when the spindle rotates once, the tool holder moves the workpiece in the Z direction by one lead.
2.Layout of CNC lathe
The layout of the spindle, tailstock and other components of the CNC lathe relative to the bed is basically the same as that of the horizontal lathe, while the layout of the tool holder and guide rails has undergone fundamental changes. This is because the layout of the tool holder and guide rails directly affects the performance of the CNC lathe and the structure and appearance of the machine tool. In addition, CNC lathes are equipped with closed protective devices.
(1) Layout of bed and guide rails
There are 4 layouts in total. Horizontal bed, inclined bed and inclined slide, horizontal bed and inclined slide, vertical bed.
The horizontal bed has good processability and is convenient for processing the guide rail surface. The horizontal bed with a horizontally configured tool holder can increase the movement speed of the tool holder. It can generally be used for the layout of large CNC lathes or small precision CNC lathes. However, the lower space of the horizontal bed is small, which makes chip removal difficult. From the perspective of structural dimensions, the horizontal placement of the tool holder makes the lateral dimension of the slide longer, thereby increasing the structural dimensions in the width direction of the machine tool.
The layout form of the horizontal bed with an inclined slide and an inclined guide rail protective cover has the characteristics of good processability of the horizontal bed on the one hand; on the other hand, the size of the machine tool in the width direction is smaller than that of the horizontal slide, and it is convenient to remove chips.
The layout form of the horizontal bed with an inclined slide and the inclined bed with an inclined slide are widely used by small and medium-sized CNC lathes. This is because these two layout forms are easy to remove chips, the chips will not accumulate on the guide rails, and it is also convenient to install automatic chip conveyors; easy to operate, easy to install manipulators to realize single-machine automation; the machine tool occupies a small area, has a simple and beautiful appearance, and is easy to achieve closed protection.
The inclined angle of the inclined bed rail can be 30°, 45°, 60°, 75° and 90° (called vertical bed). A small inclination angle makes chip removal inconvenient; a large inclination angle makes the guide rail poor in guiding and stress-bearing conditions. The size of the guide rail inclination angle will also directly affect the ratio of the height and width of the machine tool’s overall dimensions. Taking all the above factors into consideration, the inclination of the bed of small and medium-sized CNC lathes should be 60°.
(2) Layout of the tool holder
The tool holder of a CNC lathe is an important component of the machine tool. The tool holder is used to clamp cutting tools. Therefore, its structure directly affects the cutting performance and cutting efficiency of the machine tool. To a certain extent, the tool holder structure and performance reflect the design and manufacturing level of the CNC lathe. With the continuous development of CNC lathes, the tool holder structure is constantly innovating, but in general, it can be roughly divided into two categories, namely, the tool holder and the turret tool holder. Some turning centers also use automatic tool changing devices with tool magazines.
The tool holder is generally used for small CNC lathes. Various tools are arranged and clamped on a movable slide, and automatic positioning can be achieved when changing tools.
The turret tool rest is also called a turret or a tool table, and has two structural forms: vertical and horizontal. It has a multi-tool automatic positioning device, and realizes the automatic tool change action of the machine tool through the rotation, indexing and positioning of the turret head. The turret tool rest should have accurate indexing, reliable positioning, high repeated positioning accuracy, fast indexing speed, and good clamping rigidity to ensure the high precision and high efficiency of the CNC lathe. Some turret tool rests can not only realize automatic positioning, but also transmit power. At present, two-coordinate linkage lathes mostly use 12-station turret tool rests, and there are also 6-station, 8-station, and 10-station turret tool rests. There are two forms of layout of the turret tool rest on the machine tool: one is a turret tool rest for processing disc parts, whose rotary axis is subverted to the spindle; the other is a turret tool rest for processing shaft and disc parts, whose rotary axis is parallel to the spindle.
The bed of a four-axis CNC lathe is equipped with two independent slides and a turret tool holder, so it is called a double-tool holder four-axis CNC lathe. The cutting feed of each tool holder is controlled separately, so the two tool holders can cut different parts of the same workpiece at the same time, which not only expands the processing range but also improves the processing efficiency. The four-axis CNC lathe has a complex structure and needs to be equipped with a special CNC system to realize the control of the two independent tool holders. It is suitable for processing crankshafts, aircraft parts and other parts with complex shapes and large batches.