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Five-axis CNC machining center

2018-07-13 Administrator home station clicks:

introduce

Five-axis linkage is the term of numerical control, the numerical control machine tool at a certain speed at the same time to reach a set point, five-axis linkage is five axis can be. Five-axis CNC machine tool is a kind of machine tool with high technology content and high precision, which is specially used to process complex curved surface. This kind of machine tool system has a decisive influence on a country's aviation, aerospace, military, scientific research, precision equipment, high-precision medical equipment and other industries. Equipment manufacturing industry is the cornerstone of a country's industry. It provides an important means for the development of new technologies, new products and modern industrial production, and is an indispensable strategic industry. Even in the industrialized countries, great importance has been attached to it.

Development background

With the rapid development of China's national economy and the need of national defense construction, a large number of urgent demands for high-end CNC machine tools have been put forward. Machine tools are a symbol of a country's level of manufacturing. On the other hand, the machine tool manufacturing industry is represented by five-axis CNC machine tool system, which, in a sense, reflects the industrial development level of a country. For a long time, western industrial developed countries, led by the United States, have taken five-axis CNC machine tool system as an important strategic material and implemented the export license system. In particular, during the cold war, China, the former Soviet union and other socialist camps imposed a blockade and embargo. Hobby military friends may know the famous "Toshiba incident:" the end of last century, Japanese Toshiba company to sell to the former Soviet union a few five-axis linkage CNC milling machine, the result that the Soviet union used in the manufacture of submarine propulsion propeller, on a few class, the American spy ship in the sonar can't listen the voice of the submarine, so American embargo, with Toshiba violated the strategic materials to punish Toshiba.

species

Five-axis machine tools include vertical, horizontal and cradle-type two-axis NC table, NC dividing head of NC table, 90 axis of NC table, 45B axis of NC table, A axis of NC table, and two-axis NC spindle. The above six categories of a total of 7 five-axis joint modes have their own characteristics, which can not say which form is better, can only say which type of five-axis processing your product is suitable for.

(1) five-coordinate linkage dual-turntable machine tool

(A) the rotating coordinates have sufficient stroke range and good process performance.

(B) due to structural constraints, the low rigidity of the oscillating coordinates becomes the weak link of the rigidity of the whole machine tool. And double table machine, the rigidity of the table is much higher than that of the swing head, thus improving the overall rigidity of the machine.

(C) facilitate the development of processing centres. Only need to install independent tool bank and tool changing manipulator, but the coordinate drive power of double turntable machine tool is large, and the coordinate conversion relation is complex.

(2) five-coordinate two-swing head machine

The double swing head machine has low driving power, convenient loading and unloading of workpiece and simple coordinate transformation

(3) five-coordinate, one-swing, one-turntable machine

The performance of a swing head and rotary table machine tool is between the above two

The characteristics of

1. Effectively avoid tool interference

2. For straight surface parts, side milling method can be used to form one blade

3. For the general vertical surface, especially the relatively flat large surface, the end face of the large diameter milling cutter can be processed close to the surface

4. Multi-surface and multi-process processing can be carried out on multiple spatial surfaces of the workpiece in a single loading

5. In five-axis machining, the cutting tool can be in the most effective cutting state relative to the workpiece surface. The error distribution on the surface of the part is uniform

6. In some machining situations, larger size cutting tools can be used to avoid interference

Point of contact

The most widely used five-axis machining mode

The so-called point contact processing refers to the processing method of point contact forming in the process of processing, such as spherical milling cutter processing, spherical grinding wheel grinding. The main features of this processing mode are: Spherical surface normal vector pointing to full space, processing on the surface normal vector has adaptive capacity, compared with the line, surface contact processing, the programming is simpler, the computational amount is small, and as long as the tool radius is smaller than the minimum curvature radius of the surface can avoid interference. Therefore, it is suitable for machining arbitrary surfaces. However, due to the point contact forming, the cutting speed is close to zero at the cutting point, which results in poor cutting conditions, low machining accuracy and efficiency.

Surface contact

The so-called surface contact processing refers to the processing mode of surface contact forming, such as end face milling (grinding) processing. The main features of this machining method are: because the cutting point has a higher cutting speed and a larger periodic feed, it has a higher machining efficiency and accuracy. However, due to the influence of forming mode and cutter shape, it is mainly suitable for the processing of the curved surface where the curvature change is relatively flat.

Line contact

The focus of current and future research on five-coordinate CNC machining

The so-called line contact processing refers to the processing method of line contact forming in the processing process, such as circular milling, conical milling, camphor nill grinding and abrasive belt grinding. This method is characterized by high machining accuracy due to high cutting speed at the cutting point and high machining efficiency due to line contact forming.

The use of five-axis machine tool makes the clamping of workpiece easy. No special jig is needed during machining, which reduces the cost of jig, avoids multiple clamping, and improves the precision of die machining. The use of five - axis technology can reduce the number of jig. In addition, the five-axis machine tool can save many special tools in processing, so the cost of cutting tools is reduced. The five-axis machine tool can increase the effective cutting edge length, reduce cutting force, improve tool life and reduce cost in machining.

The five-axis machine tool can finish the mold processing quickly, deliver goods quickly, better guarantee the mold processing quality, make the mold processing more easy, and make the mold modification easier. In traditional die processing, vertical machining center is usually used to finish the milling of the workpiece. With the development of mould manufacturing technology, some weakness of vertical machining center is more and more obvious. Modern mold processing generally use ball head milling cutter for machining the ball milling cutter head in mould processing benefit is very obvious, but if use vertical machining center, the bottom of the linear velocity is zero, so bottom surface degree of finish is very poor, if you use four, five-axis linkage machining technology in mold processing, can overcome the above shortcomings.

The development trend

At present, foreign five-axis CNC machine tools, represented by Europe, America and Japan, represent the highest level of development of today's five-axis CNC machine tools. The overseas famous machine tool plant five-axis CNC machine tool technology development focus can be summarized as: high speed, high precision, environmental protection, intelligent, compound. The torque motor is widely used as the driving device of rotary coordinates in foreign countries, which makes the feeding mechanism of foreign machine achieve the goal of high speed, low loss, high accuracy and high efficiency.

The first is the use of linear motor drive technology. After more than ten years of development, linear motor technology has been very mature. The problem of easy interference and high heat generation of linear motor has been solved recently. The positioning technology of linear motor not only stops rapidly in high-speed movement, but also some machine tool manufacturers use damping technology to solve the problem. The advantages of linear motor are linear drive, no transmission chain, no wear and no reverse clearance, so it can achieve the best positioning accuracy. Linear motor has high dynamic performance with acceleration over 2g. Using linear motor drive also has the characteristics of high reliability and maintenance free.

The second is the use of dual - drive technology. For the wider worktable or gantry frame type, if the intermediate drive is adopted, the driving force cannot be guaranteed in the center in practice, which is easy to cause tilt, resulting in poor dynamic performance. Using a double drive, double grating ruler, one driver module, you can make the dynamic performance very perfect. A driver instruction, dual drive work at the same time, the grating ruler to detect whether the two points are balanced, if not balanced through different instructions to achieve balance. Of course, the development of five-axis machine tool technology is far more than that, many technologies will be reflected in demarge's machine tool products.

Strategic significance

Because the five-axis CNC machine tool system is very expensive and the NC program is difficult to make, it is difficult to use the five-axis system. Along with the computer aided design (CAD), computer aided manufacturing (CAM) system has obtained the breakthrough development of bashan star company many CNC companies such as China, have launched five-axis linkage CNC machine system, to break the blockade of foreign technology, occupied the vertices of the strategic industries, greatly reduce the cost of the application to China's equipment manufacturing industry ushered in a new era! The development of modern science represented by information technology has injected strong impetus to the equipment manufacturing industry, and also put forward stronger requirements for it, highlighting the irreplaceable role of machinery equipment manufacturing industry as the carrier of high-tech industrialization in promoting the whole social technological progress and industrial upgrading. As the driving force of national economic growth and technological upgrading, the machinery and equipment manufacturing industry marked by five-axis linkage will progress together with the development of new and high technologies and emerging industries. China should not only be a world manufacturing power, but also a world manufacturing power! It is estimated that with the popularization of five-axis CNC machine tool system in the near future, it will lay a solid foundation for China to become the world's strongest country!

The value of

Machining center

Generally, the machining center is divided into vertical machining center and horizontal machining center. The most effective machining surface of vertical machining center (three-axis) is only the top surface of the workpiece. Horizontal machining center can only complete four sides machining of the workpiece with the help of rotary table. The top-grade machining center is developing towards five-axis control. The five-axis machining center is characterized by high efficiency and high accuracy, and the workpiece can complete the five-sided machining with a single clamping. For example, the advanced numerical control system with five-axis linkage can also process complex space curved surface with high precision, which is more suitable for the processing of modern molds such as automobile parts and aircraft structural parts. Vertical five-axis machining center there are two ways of rotating the center of vertical five-axis machining. The table set on the bed can rotate around the X-axis, defined as the a-axis, which generally has A working range of +30 to -120 degrees. There is also a rotary table in the middle of the table, which is rotated around the Z axis in the position shown, defined as C axis, which is 360 degrees of rotation. Thus, through the combination of axis A and axis C, the workpiece fixed on the working table can be processed by the vertical spindle except the bottom surface. The minimum dividing value of A and C axes is generally 0.001. In this way, the workpiece can be subdivided into any Angle to produce inclined surface and inclined hole. If the a-axis and c-axis are interconnected with the XYZ trilinear axis, complex space surfaces can be processed, which of course requires the support of high-end CNC systems, servo systems and software. The advantage of this setting mode is that the spindle structure is relatively simple, the spindle rigidity is very good, and the manufacturing cost is relatively low. However, the work table generally cannot be designed to be too large, and the bearing capacity is small, especially when the A axis rotation is greater than or equal to 90 degrees, the workpiece cutting will bring A large bearing capacity moment to the work table. The other depends on the vertical spindle head rotation. The front end of the spindle is A rotating head, which can wrap around the z-axis 360 degrees on its own to become the c-axis. The head of the spindle is also equipped with A axis that can rotate around the X-axis, which can generally be more than + / -90 degrees, realizing the same function mentioned above. The advantage of this setting method is that the spindle processing is very flexible, and the table can be designed to be very large. The large body of the aircraft and the huge engine housing can be processed in this kind of processing center. This design has a big advantage: we are using spherical milling cutter machining curved surface, when cutting tool processing center line perpendicular to the surface, as a result of the spherical milling cutter vertex linear velocity is zero, the vertices will cut the workpiece surface quality is very poor, adopts the design of spindle, the spindle relative to the workpiece around a point of view, the spherical milling cutter cutting, avoid the vertex ensure that there is a certain linear velocity, to improve the quality of surface processing. This kind of structure is very popular for high-precision surface machining of mould, which is difficult to be achieved by rotary machining center of table. In order to achieve high precision of rotation, the high-grade rotary shaft is equipped with circular grating scale feedback, and the precision is within a few seconds. Of course, the rotary structure of such spindle is more complex, and the manufacturing cost is higher.