According to the definition in GB/T 12204-2010, the spindle box is a box-shaped component that houses the spindle. The spindle box is an important component of the machine tool. It is used to arrange the machine tool's working spindle, its transmission parts and corresponding additional mechanisms. The spindle box is a complex transmission component, including the spindle assembly, reversing mechanism, transmission mechanism, braking device, operating mechanism and lubrication device. Its main function is to support the spindle and rotate it to realize the functions of starting, braking, speed changing and reversing the spindle.
(This article is selected from Chapter 2, Section 3 of the "Machining Center Selection Guide" The Spindle Box of the Machining Center)
The spindle component of the machining center is composed of spindle power, transmission and spindle components. It is one of the important execution components of the forming movement of the machining center. Therefore, the spindle component of the machining center is required to have high operating accuracy, long-term accuracy retention and long-term operation. accuracy stability.
Machining centers are usually used as precision machine tools, and the running accuracy of the spindle components determines the machining accuracy of the machine tool. There are generally two methods to assess the operating accuracy of machine tools: static inspection and dynamic inspection. Static inspection refers to testing the runout of each positioning surface and working surface of the spindle component when the spindle is rotated at low speed or manually. Dynamic inspection requires the use of certain instruments to test the rotation accuracy of the spindle using non-contact detection methods at the rated speed of the machine tool spindle. Since machining centers usually have automatic tool changing functions, and the tools are tightened by a tensioning mechanism installed inside the spindle of the machining center through a special tool holder, the rotation accuracy of the spindle must consider the error caused by the machining error of the tool holder positioning surface.
1. Requirements that the main transmission system should meet
The machining center is a CNC machine tool with strong versatility, wide application range and high processing efficiency. Therefore, its main transmission system must meet four requirements: First, it has a wide speed range; second, it not only has sufficient power and torque, but also can Meet the requirements of maintaining constant power under high-speed conditions (above the calculated speed) and maintaining constant torque under low-speed conditions (below the calculated speed); third, the components of the spindle box should have sufficient strength, stiffness and vibration resistance; fourth, operation Smooth and low noise.
2. Typical structure of spindle box and electric spindle
1. Typical structure of spindle box
(1) One-stage poly-V belt drive spindle box. The main motor power of the spindle box is below 7.5kW. The first-stage poly-V belt (composite V-belt) transmission form is often used. The main motor passes through a pair of poly-V belt pulleys and a poly-V belt. The belt is connected to the main shaft, and a speed reduction transmission method is used to increase the torque.
(2)) The gear transmission spindle box generally uses a first-stage expansion group to increase the speed range and improve low-speed torque. Since there are only two gears, high and low, the transmission mechanism is relatively simple.
(3) Direct-coupled spindle box Direct-coupled spindle box refers to a spindle box in which the spindle motor and the spindle are directly connected. There are two direct connection methods for direct-coupled spindle boxes: one is that the main motor is connected to the spindle through a coupling; the other is that the main motor is made into a spindle box, the rotor is designed as a spindle, and the stator is installed in the spindle box Inside.
2. Electric spindle
The machine tool spindle refers to the axis on the machine tool that drives the workpiece or tool to rotate. It usually consists of a spindle, bearings and transmission parts (gears or pulleys). With the rapid development and improvement of electrical transmission technology, the mechanical structure of the main transmission system of high-speed CNC machine tools has been greatly simplified, and pulley transmission and gear transmission have been eliminated. The machine tool spindle is directly driven by a built-in motor. This transmission structure in which the spindle motor and the machine tool spindle are "combined into one" is called an "electric spindle". It makes the spindle components independent from the machine tool's transmission system and overall structure.
The electric spindle not only has the advantages of compact structure, light weight, small inertia, low noise and fast response, but also has high rotation speed and high power, which can simplify the design of machine tools and facilitate spindle positioning. It is an ideal structure in high-speed spindle units. The electric spindle bearing adopts high-speed bearing technology, is wear-resistant and heat-resistant, and has a service life several times that of traditional bearings. Figure 2-26 shows the actual electric spindle.
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Figure 2-26 Actual electric spindle
Table 2-2 shows the parameters of the electric spindle of a certain brand of machining center. As can be seen from the table, depending on the processing materials and processes, the same model of machining center can use electric spindles with different speeds and torques. The emergence of dual-spindle or even multi-axis machining centers has further improved the processing efficiency of machining centers.
Table 2-2 Electric spindle parameters of a certain brand of machining center
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Motorized spindles often require different media to function. For example, compressed air needs to be introduced to achieve air sealing of the spindle, cooling water must be introduced to cool the interior of the spindle, and hydraulic oil must be introduced to achieve clamping of the tool holder. Therefore, the key component of the rotary joint is required to pass the medium at the rear end of the rotating spindle. Figure 2-27 shows the actual rotary joint.
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Figure 2-27 Actual rotary joint
The principle of the rotary joint is shown in Figure 2-28. The medium passes through the fixed pipelines P1 and P2 into the component 2 of the rotary joint. The component 2 remains fixed, and the component 1 can rotate with the main shaft. Both components 1 and 2 can be realized. The passage of medium can ensure good sealing. This kind of rotary joint is widely used in various types of spindles. It is worth noting that due to runout at the rear end of the spindle, this part will be damaged after a period of use. If the spindle itself has a large runout, it will accelerate the damage of the rotating joint.
