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Structure and characteristics of Machining Centers

Time: 2023-05-24 View: 157 Burst:

1、 The structure of the machining center:
The machining center is also composed of a spindle box, tool holder, feed transmission system, bed, hydraulic system, cooling system, lubrication system, etc. However, there are fundamental differences in the structure between the feed system of the machining center and the feed system of the horizontal lathe. The movement of the spindle of the horizontal lathe is transmitted to the tool holder through the change wheel frame, feed box, and slide box, achieving longitudinal and transverse feed motion. The machining center uses a servo motor, which is transmitted to the sliding plate and tool holder through a ball screw, to achieve z-direction (longitudinal) and positional (transverse) feed motion. The motion relationship between the spindle rotation of the machining center and the movement of the tool holder is controlled by the CNC system. There is a pulse encoder installed in the spindle box of the machining center, and the movement of the spindle is brought to the pulse encoder through synchronous tooth shape. When the spindle rotates, the pulse encoder sends a detection pulse signal to the CNC system, ensuring that the rotation of the spindle motor and the cutting feed of the tool holder maintain the motion relationship required for thread processing. This means that when processing threads, the spindle rotates once and the tool holder moves the workpiece one lead in the z-direction.
2、 Layout of the machining center:
The layout of the spindle, tailstock, and other components of the machining center relative to the bed is basically the same as that of a horizontal lathe, while the layout of the tool holder and guide rail has undergone fundamental changes. This is because the layout of the tool holder and guide rail directly affects the performance of the machining center and the structure and appearance of the lathe. In addition, the machining centers are equipped with enclosed protective devices.
(1) Layout of the bed and guide rails. The relative position of the machining center bed guide rail and the horizontal plane is shown in Figure 1-13, with a total of 4 layout forms.
The horizontal bed has good craftsmanship and is convenient for processing the guide rail surface. The horizontal bed equipped with a horizontally configured tool holder can improve the movement speed of the tool holder, and can generally be used for the layout of large machining centers or small precision machining centers. However, the small space under the horizontal bed makes it difficult to remove debris. From the perspective of structural dimensions, the horizontal placement of the tool holder results in a longer lateral dimension of the sliding plate, thereby increasing the structural size of the machine tool in the width direction.
The layout of a horizontal bed equipped with inclined sliding plates and inclined guide rail protective covers, on the one hand, has the characteristics of good craftsmanship of the horizontal bed; On the other hand, the size of the width direction of the machine tool is smaller than that of the horizontally configured sliding plate, and it is convenient for chip removal.
The layout of a horizontal bed with inclined sliding plates and an inclined bed with inclined sliding plates is widely adopted by small and medium-sized machining centers. This is because these two layout forms are easy to remove chips, and chips will not accumulate on the guide rail, making it easy to install an automatic chip conveyor; Easy to operate and install the robotic arm to achieve single machine automation; The machine tool occupies a small area, has a simple and beautiful appearance, and is easy to achieve closed protection.
The inclination angles of the inclined bed guide rail can be 30 °, 45 °, 60 °, 75 °, and 90 ° (referred to as vertical machining centers), among others. Small inclination angle, inconvenient chip removal, large inclination angle, poor guidance of the guide rail, and poor stress situation. The inclination angle of the guide rail also directly affects the ratio of the height to width of the machine tool's overall dimensions. Taking into account all the above factors, it is advisable for small and medium-sized machining centers to have a bed inclination of 60 °.
(2) The layout of the tool holder. The tool holder of a machining center is an important component of a machine tool, which is used to hold cutting tools. Therefore, its structure directly affects the cutting performance and efficiency of the machine tool. To some extent, the structure and performance of the tool holder reflect the design and manufacturing level of the machining center. With the continuous development of machining centers, the structural forms of tool holders continue to innovate, but overall, they can be roughly divided into two categories, namely row type tool holders and turret type tool holders. Some turning centers also use automatic tool changing devices with tool libraries.
The row type tool holder is generally used in small machining centers, where various tools are arranged and clamped on movable sliding plates, and automatic positioning can be achieved when changing tools.
Turret turret, also known as turret or turret, has two structural forms: vertical and horizontal. Equipped with a multi tool position automatic positioning device, the automatic tool change action of the machine tool is achieved through the rotation, indexing, and positioning of the turret head. The turret type tool holder should have accurate indexing, reliable positioning, high repeated positioning accuracy, fast indexing speed, and good clamping performance to ensure the high accuracy and efficiency of the machining center. Some turret type tool holders can not only achieve automatic positioning, but also transmit power. At present, two coordinate linkage lathes mostly use 12 station turret tool holders, and there are also 6 station, 8 station, and 10 station turret tool holders. There are two forms of layout of turret type tool holders on machine tools: one is a turret type tool holder used for processing disk parts, with its rotation axis perpendicular to the main shaft; Another type is a turret type tool holder used for machining shaft and disc parts, with its rotating axis parallel to the main shaft.
The machining center of the four coordinate cutting machine is equipped with two independent sliding plates and a turret type tool holder on the bed, hence it is called a dual tool holder four coordinate machining center. Among them, the cutting feed of each tool holder is controlled separately, so two tool holders can simultaneously cut different parts of the same workpiece, expanding the processing range and improving processing efficiency. The four axis machining center has a complex structure and requires a specialized CNC system to control two independent tool holders. It is suitable for machining complex shaped and large batch parts such as crankshafts and aircraft parts.