With the rapid development of numerical control technology, "combination, high speed, intelligence, precision and environmental protection" has become the main trend of technological development in machine tool industry. Among them, high-speed machining can effectively improve the machining efficiency of machine tools and shorten the machining cycle of workpieces. This requires the machine tool spindle and its related components to meet the needs of high-speed machining.
Electric spindle is a new technology that combines spindle and spindle motor in the field of CNC machine tools in recent years. Together with linear motor technology and high-speed tool technology, it will push high-speed machining to a new era. The motorized spindle is a set of components, including the motorized spindle itself and its accessories: motorized spindle, high-frequency frequency conversion device, oil mist lubricator, cooling device, built-in encoder and tool changing device.
Electric spindle integration technology;
High-speed bearing technology: the motorized spindle usually adopts composite ceramic bearings, which are wear-resistant and heat-resistant, and their service life is several times that of traditional bearings; Sometimes electromagnetic bearings or hydrostatic bearings are used, and the inner and outer rings are not in contact, so the service life is infinite in theory;
High-speed motor technology: motorized spindle is the product of the integration of motor and spindle, and the rotor of motor is the rotating part of spindle. Theoretically, the motorized spindle can be regarded as a high-speed motor. The key technology is high-speed dynamic balance;
Lubrication: the lubrication of motorized spindle generally adopts periodic quantitative oil-gas lubrication; It can also be lubricated with grease, but the corresponding speed should be discounted. The so-called timing means spraying oil every once in a while. The so-called quantification is to accurately control the amount of lubricating oil each time through a device called a quantitative valve. Oil-gas lubrication is to blow lubricating oil into ceramic bearings with the help of compressed air. Oil quantity control is very important, too little, and it can't play a lubricating role; Too much, the bearing will heat up due to the resistance of oil when it rotates at high speed.
Cooling device: In order to dissipate heat for high-speed motorized spindle as soon as possible, circulating cooling liquid is usually introduced into the outer wall of motorized spindle, and the function of cooling device is to keep the temperature of cooling liquid.
Built-in pulse encoder: In order to realize automatic tool change and rigid tapping, the motorized spindle has built-in pulse encoder to realize accurate phase angle control and cooperation with feed.
Automatic tool changing device: in order to be used in machining center, the motorized spindle is equipped with automatic tool changing device, including disc spring, broach cylinder and so on.
Clamping method of high-speed tools: The well-known BT and ISO tools have been proved to be unsuitable for high-speed machining. In this case, HSK, SKI and other high-speed tools appeared.
High-frequency frequency conversion device: To realize the rotating speed of the motorized spindle of tens of thousands or even hundreds of thousands of revolutions per minute, the high-frequency frequency conversion device must be used to drive the high-speed motor built in the motorized spindle, and the output frequency of the frequency converter must reach several thousand or several thousand hertz.
CNC lathe is one of the most widely used CNC machine tools at present. It is mainly used for cutting internal and external cylindrical surfaces, internal and external conical surfaces with arbitrary cone angles, complex revolving internal and external curved surfaces, cylindrical surfaces and tapered threads of shaft parts or disc parts, and can be used for slotting, drilling, reaming and boring. The NC machine tool automatically processes the machined parts according to the pre-programmed processing program. According to the instruction code and program format specified by the NC machine tool, we write the processing route, process parameters, tool path, displacement, cutting parameters and auxiliary functions of the parts into a processing program sheet, and then record the contents of this program sheet on the control medium, and then input it into the NC device of the NC machine tool, thus guiding the machine tool to process parts.
With the continuous development of numerical control technology and the continuous expansion of its application fields, it plays an increasingly important role in the development of some important industries (IT, automobile, light industry, medical care, etc.). ) of the national economy and people's livelihood, because the digitalization of the equipment needed in these industries has become the general trend of modern development. Generally speaking, CNC lathes present the following three development trends:
1, high speed and high precision
High speed and precision are the eternal goals of machine tool development. With the rapid development of science and technology, the upgrading speed of mechanical and electrical products is accelerated, and the requirements for machining accuracy and surface quality of parts are getting higher and higher. In order to adapt to this complex and changeable market demand, machine tools are developing in the direction of high-speed cutting, dry cutting and quasi-dry cutting, and the machining accuracy is constantly improving. On the other hand, the successful application of motorized spindle and linear motor, the introduction of ceramic ball bearings, the low-temperature high-speed ball screw pair with high precision and large lead hollow internal cooling and ball nut strong cooling, and the linear guide pair with ball cage have also created conditions for the high-speed and precise development of machine tools.
The CNC lathe adopts electric spindle, which eliminates the links of belt, pulley and gear, greatly reduces the moment of inertia of the main drive, improves the dynamic response speed and working accuracy of the spindle, and completely solves the vibration and noise problems of the belt and pulley drive when the spindle runs at high speed. The motorized spindle structure can make the spindle speed reach more than 10000 rpm.
Linear motor has high driving speed, good acceleration and deceleration characteristics, excellent response characteristics and following accuracy. The linear motor is used as the servo drive, which saves the intermediate transmission link of the ball screw, eliminates the transmission gap (including the reverse gap), has small inertia, good system rigidity, can accurately position at high speed, and greatly improves the servo accuracy.
The linear rolling guide rail pair, because of its zero clearance in all directions, has very small rolling friction, little wear, negligible heating and excellent thermal stability, which improves the positioning accuracy and repeated positioning accuracy of the whole process. Through the application of linear motor and linear rolling guide pair, the fast moving speed of machine tool can be increased from 10 ~ 20m/mim to 60 ~ 80m/min, and the highest speed can reach 120m/min.
2, high reliability
The reliability of CNC machine tools is the key index of product quality of CNC machine tools. Whether the CNC machine tool can exert its high performance, high precision, high efficiency and achieve good benefits depends on its reliability.
3, CNC lathe design CAD, modular structure design.
With the popularization of computer application and the development of software technology, CAD technology has been widely developed. CAD can not only replace manual drawing, but also choose design scheme, analyze, calculate, predict and optimize static and dynamic characteristics of large machines, and dynamically simulate all working parts of machines. On the basis of modularization, we can see the three-dimensional geometric model and realistic color of the product in the design stage. Using CAD can also greatly improve the work efficiency and the first success rate of design, thus shortening the trial production cycle, reducing the design cost and improving the market competitiveness.
Variable speed mode of CNC machine tools;
1, stepless speed change
CNC machine tools generally use DC or AC spindle servo motor to realize stepless speed change of spindle.
The AC spindle motor and AC variable frequency drive device (squirrel-cage induction AC motor with vector transformation variable frequency speed regulation system) have long service life because of no brush and spark, and their performance has reached the level of DC drive system, even in noise. So it is widely used at present.
The relationship between the power or torque transmitted by the spindle and the rotational speed. When the machine tool runs continuously, the spindle speed is in the range of 437~3500r/min, and the spindle transmits all the power of the motor, which is the spindle constant power zone II (solid line). In this region, the maximum output torque (245N.m) of the spindle decreases with the increase of spindle speed. When the spindle speed is in the range of 35~437r/min, the output torque of the spindle is constant, which is called the constant torque zone I (solid line) of the spindle. In this area, the power that the spindle can transmit decreases with the decrease of spindle speed. The dotted line in the figure indicates the constant power area and constant torque area when the motor is overloaded (overload is allowed for 30 minutes). Motor overload power 15kW, and the maximum overload output torque is 334N.m.
2. Step by step stepless speed change
In actual production, CNC machine tools do not need constant power in the whole speed range. Generally, the middle and high speed section requires constant power transmission, and the low speed section requires constant torque transmission. In order to ensure that the spindle of CNC machine tools has a large torque at low speed and the speed range of the spindle is as large as possible, some CNC machine tools are equipped with gear speed change on the basis of stepless speed change of AC or DC motors, making it a segmented stepless speed change.