With the rapid development of CNC technology, "composite, high-speed, intelligent, precision, environmental protection" has become the main trend of technological development of today's machine tool industry. Among them, high-speed machining can effectively improve the machining efficiency of the machine tool, shorten the processing cycle of the workpiece. This requires the machine tool spindle and its related components to adapt to the needs of high-speed machining.
Electrospindle is the last few years in the field of CNC machine tools will appear in the machine tool spindle and spindle motor into one of the new technology, which, together with linear motor technology, high-speed tooling technology, high-speed machining will be pushed to a new era. The electric spindle is a set of components, which includes the spindle itself and its accessories: electric spindle, high-frequency frequency conversion device, oil mist lubricator, cooling device, built-in encoder, tool changer.
The technology integrated by the spindle:
High-speed bearing technology: the spindle usually adopts composite ceramic bearings, which are wear-resistant and heat-resistant, with a life span of several times that of the traditional bearings; and sometimes it also adopts electromagnetic levitation bearings or static bearings, with the inner and outer rings not in contact, and theoretically with unlimited life span;
High-speed motor technology: the spindle is a product of the fusion of the electric motor and the main spindle, and the electric motor's The rotor is the rotating part of the spindle, and theoretically the spindle can be regarded as a high-speed motor. The key technology is dynamic balancing at high speeds;
Lubrication: the lubrication of the spindle is generally timed quantitative oil and gas lubrication; grease lubrication can also be used, but the corresponding speed should be discounted. The so-called timing, is every certain time interval oil injection. The so-called quantitative, is through a device called quantitative valve, precise control of each time the amount of oil lubricant. Oil-air lubrication, on the other hand, refers to the lubricant being blown into the ceramic bearing, carried by compressed air. Oil volume control is very important, too little, can not play a lubricating role; too much, in the bearing high-speed rotation will be due to the resistance of the oil and heat.
Cooling device: In order to dissipate the heat of the high-speed running spindle as soon as possible, the outer wall of the spindle is usually passed through the circulating coolant, and the role of the cooling device is to maintain the temperature of the coolant.
Built-in pulse encoder: In order to realize automatic tool change and rigid thread tapping, a pulse encoder is built into the motor spindle to realize accurate phase angle control and coordination with the feed.
Automatic tool changer: In order to be used in machining centers, the motor spindle is equipped with automatic tool changer, including disc spring, tool pulling cylinder, etc.
High-speed tool loading: The familiar BT and ISO tools have been proved to be unsuitable for high-speed machining. This situation appears HSK, SKI and other high-speed tools.
High-frequency frequency conversion device: to realize the spindle speed of tens of thousands or even hundreds of thousands of revolutions per minute, a high-frequency frequency conversion device must be used to drive the spindle's built-in high-speed motor, the frequency converter's output frequency must be up to thousands or thousands of hertz.
CNC lathe is one of the more widely used CNC machine tools. It is mainly used for shaft parts or disk parts of the internal and external cylindrical surface, any taper angle of the internal and external conical surface, complex rotary internal and external surfaces and cylindrical, tapered threads, such as cutting and processing, and can be grooving, drilling, reaming, reaming and boring. CNC machine tool is in accordance with the pre-programmed machining program, automatically processed parts. We put the parts of the machining process route, process parameters, tool trajectory, displacement, cutting parameters and auxiliary functions, in accordance with the provisions of the CNC machine tool instruction code and program format written into a processing program list, and then the contents of this program list is recorded in the control media, and then entered into the CNC machine tool in the CNC device, so as to command the machine tool to process the parts.
With the continuous development of CNC technology and the expansion of the field of application, it is on the national economy and people's livelihood of a number of important industries (IT, automotive, light industry, medical, etc.) of the development of an increasingly important role, because of the digitalization of the equipment required by these industries has been a major trend in modern development. In general, CNC lathes show the following three trends:
1, high-speed, high-precision
High-speed, precision is the eternal goal of machine tool development. With the rapid development of science and technology, electromechanical products to accelerate the speed of replacement, the precision of parts processing and surface quality requirements are getting higher and higher. In order to meet the needs of this complex and changing market, the current machine tool is to high-speed cutting, dry cutting and quasi-dry cutting direction, machining accuracy is also constantly improving. On the other hand, the successful application of electric spindles and linear motors, ceramic ball bearings, high-precision large-conductivity hollow internal cooling and ball nut cooling of low-temperature and high-speed ball screws and linear guides with ball retainers and other machine tool functional components of the market, but also for the machine tool to high-speed, precision development has created the conditions.
Numerical control lathe with electric spindle, the elimination of the belt, pulley and gears and other links, greatly reducing the rotational inertia of the main drive, improve the dynamic response speed of the spindle and working accuracy, completely solve the spindle high-speed operation of the belt and pulley transmission vibration and noise problems. The use of electric spindle structure can make the spindle speed of 10000r/min or more.
Linear motor drive speed is high, acceleration and deceleration characteristics are good, with superior response characteristics and following accuracy. Servo drive with linear motor, eliminating the ball screw as an intermediate transmission link, eliminating the transmission gap (including backlash), small motion inertia, good system rigidity, precision positioning at high speeds, thus greatly improving the servo accuracy.
Linear rolling guide vice, because it has zero clearance in all directions and very small rolling friction, wear and tear is small, the heat is negligible, there is a very good thermal stability, improves the whole process of positioning accuracy and repeatability of positioning accuracy. Through the application of linear motors and linear rolling guide vice, can make the machine tool rapid traverse speed from 10 ~ 20m/mim increased to 60 ~ 80m/min, up to 120m/min.
2, high reliability
Reliability of CNC machine tools is a key indicator of the quality of the product of CNC machine tools. CNC machine tools can play its high performance, high precision and high efficiency, and get good benefits, the key depends on its reliability.
3, CNC lathe design CAD, modular structural design
With the popularization of computer applications and the development of software technology, CAD technology has been widely developed.CAD can not only replace the manual completion of the tedious work of drawing, more importantly, can be designed to select and large parts of the machine static and dynamic characteristics of the analysis, calculations, prediction and optimization of the design can be Dynamic simulation simulation of each working part of the whole machine. On the basis of modularity in the design stage can be seen in the three-dimensional geometric model of the product and realistic color. The use of CAD, but also can greatly improve the efficiency of work, improve the design of a success rate, thereby shortening the trial period, reduce design costs, improve market competitiveness.
CNC machine tool speed mode:
1, stepless speed
CNC machine tools generally use DC or AC spindle servomotor to achieve stepless spindle speed.
AC spindle motor and AC frequency drive (cage induction AC motor configuration vector conversion frequency control system), because there is no brush, does not produce sparks, so the long service life, and performance has reached the level of DC drive system, and even in the noise has been reduced. Therefore, the current application is more widely used.
The relationship between the power or torque transmitted by the spindle and the speed. When the machine tool is in continuous operation, the spindle speed in the range of 437~3500r/min, the spindle to transfer all the power of the motor 11kW, for the spindle constant power region Ⅱ (solid line). In this region, the maximum output torque (245N.m) of the spindle becomes smaller as the spindle speed increases. The spindle speed in the range of 35~437r/min, the output torque of the spindle is unchanged, which is called the constant torque region Ⅰ (solid line) of the spindle. In this region, the power that can be transmitted by the spindle decreases as the spindle speed decreases. The dotted line in the figure shows the constant power region and constant torque region when the motor is overloaded (allowed to be overloaded for 30 min). The overload power of the motor is 15kW, and the maximum output torque of overload is 334N.m.
2, segmented stepless variable speed
CNC machine tools in actual production do not require constant power throughout the entire variable speed range. General requirements in the medium and high speed section for constant power transmission, in the low speed section for constant torque transmission. In order to ensure that the spindle of the CNC machine tool has a large torque at low speeds and the spindle speed range as large as possible, some CNC machine tools in the AC or DC motor stepless speed on the basis of gear speed, making it a segmented stepless speed.