The functions and advantages of the three-axis machining center:
The most effective machining surface of the vertical machining center (three-axis) is only the top surface of the workpiece, and the horizontal machining center can only complete the four-sided machining of the workpiece with the help of the rotary table. At present, the high-end machining center is moving towards the direction of five-axis control, and the workpiece can be processed with a pentahedron in one clamping. If equipped with a five-axis linkage high-end CNC system, it can also perform high-precision machining of complex spatial surfaces.
Four-axis simultaneous machining
The so-called four-axis linkage machining generally adds a rotation axis, usually called the fourth axis. The general machine tool has only three axes, that is, the workpiece platform can move left and right (1 axis), front and back (2 axes), and the spindle head (3 axis) is used to cut the workpiece. The fourth axis is to install a 360 degree on the moving platform. Rotating electric indexing head! In this way, it is possible to automatically index and drill beveled holes, milling beveled edges, etc., without the need for secondary clamping to lose accuracy.
Features of four-axis simultaneous machining:
(1). The three-axis linkage processing machine tool cannot be processed or needs to be clamped too long
(2). Improve the accuracy, quality and efficiency of free space surfaces
(3). The difference between four-axis and three-axis; the difference between four-axis and three-axis and the establishment of four-axis coordinates with one more rotation axis and
The representation of the code:
Determination of Z-axis: The axis direction of the machine tool spindle or the vertical direction of the worktable where the workpiece is clamped is the Z-axis. The direction away from the spindle axis is the positive direction.
Vertical five-axis machining center
There are two ways for the rotary axis of this type of machining center, one is the table rotary axis.
The worktable set on the bed can rotate around the X axis, which is defined as the A axis. The general working range of the A axis is +30 degrees to -120 degrees. There is also a rotary table in the middle of the worktable, which rotates around the Z axis at the position shown in the figure, which is defined as the C axis, and the C axis all rotates 360 degrees. In this way, through the combination of A-axis and C-axis, except for the bottom surface of the workpiece fixed on the worktable, the other five surfaces can be processed by the vertical spindle. The minimum index value of A-axis and C-axis is generally 0.001 degree, so that the workpiece can be subdivided into any angle, and inclined surface, inclined hole and so on can be processed.
If the A-axis and C-axis are linked with the XYZ three linear axes, complex spatial surfaces can be processed. Of course, this requires the support of high-end CNC systems, servo systems and software. The advantage of this arrangement is that the structure of the main shaft is relatively simple, the rigidity of the main shaft is very good, and the manufacturing cost is relatively low.
However, the general worktable cannot be designed too large, and the load-bearing capacity is also small, especially when the A-axis rotation is greater than or equal to 90 degrees, the worktable will have a large load-bearing moment when the workpiece is cut.
The front end of the spindle is a swivel head that can circumnavigate the Z axis 360 degrees to become the C axis. The swivel head also has an A axis that can rotate around the X axis, which can generally reach more than ±90 degrees to achieve the same function as above. The advantage of this setting method is that the spindle processing is very flexible, the worktable can also be designed to be very large, and the huge fuselage and huge engine shell of the passenger aircraft can be processed on this type of machining center.
This design has another big advantage: when we use a spherical milling cutter to process curved surfaces, when the center line of the tool is perpendicular to the processing surface, since the linear velocity of the apex of the spherical milling cutter is zero, the surface quality of the workpiece cut by the apex will be poor. The spindle rotation design is adopted to make the spindle rotate at an angle relative to the workpiece, so that the spherical milling cutter avoids the apex cutting, guarantees a certain linear speed, and improves the surface processing quality. This structure is very popular for high-precision surface machining of molds, which is difficult for rotary table machining centers to achieve. In order to achieve the high precision of rotation, the high-end rotary axis is also equipped with circular grating scale feedback, and the indexing accuracy is within a few seconds. Of course, the rotation structure of this type of spindle is more complicated and the manufacturing cost is also high.
Vertical five-axis machining center with spindle rotation
The gravity of the main shaft of the vertical machining center is downward, the radial force of the bearing in high-speed dry running is equal, and the rotation characteristics are good, so the speed can be increased. Generally, the high speed can reach more than 1,2000r/min, and the practical maximum speed has reached 4,0000 revolutions. The main shaft system is equipped with a circulating cooling device. The circulating cooling oil takes away the heat generated by high-speed rotation, reduces it to a suitable temperature through the refrigerator, and then flows back to the main shaft system.
The X, Y, and Z three linear axes can also use linear grating feedback, and the bidirectional positioning accuracy is within micrometers. Since the rapid feed rate is more than 40-60m/min, most of the ball screws of X, Y, Z axis adopt central cooling. Like the spindle system, the refrigerated circulating oil flows through the center of the ball screw to take away heat. .
Horizontal five-axis machining center
There are also two ways for the rotary axis of this type of machining center. One is that the horizontal spindle swings as a rotary axis, and a rotary axis of the worktable is added to realize five-axis simultaneous machining. This setting method is simple and flexible. If the spindle needs to be converted from vertical to horizontal, the worktable can be easily configured as a vertical-to-horizontal three-axis machining center by indexing and positioning. The vertical and horizontal conversion of the spindle cooperates with the indexing of the worktable to realize the pentahedral processing of the workpiece, which reduces the manufacturing cost and is very practical. It is also possible to set a numerical control axis for the worktable, with a minimum index value of 0.001 degrees, but without linkage, it becomes a four-axis machining center for vertical and horizontal conversion, adapting to different processing requirements, and the price is very competitive.
The other is the traditional rotary axis of the worktable. The A-axis of the worktable set on the bed has a general working range of +20 degrees to -100 degrees. There is also a rotary table B axis in the middle of the worktable, and the B axis can rotate 360 degrees in both directions. This horizontal five-axis machining center has better linkage characteristics than the first method, and is often used to process complex curved surfaces of large impellers. The rotary axis can also be equipped with circular grating scale feedback, and the indexing accuracy can reach a few seconds. Of course, this kind of rotary axis structure is more complicated and expensive.
At present, the worktable of the horizontal machining center can be larger than 1.25m2, which has no effect on the first five-axis setting mode. But the second five-axis setting method is more difficult, because the 1.25m2 worktable does the A-axis rotation, and it is really difficult to link with the B-axis turntable in the middle of the worktable. The spindle speed of the horizontal machining center is generally above 10,000rpm. Because the horizontally set spindle has self-gravity in the radial direction, the radial force of the bearing is uneven when the bearing is running at high speed. In addition, a larger BT50 tool holder must be used. Generally up to 20,000rpm. The rapid feed rate of the horizontal machining center is more than 30-60m/min, the power of the spindle motor is more than 22-40KW, and the capacity of the tool magazine can be increased from 40 tools to 160 tools as needed. The processing capacity is far more than the general vertical machining center. It is heavy-duty The first choice for machining.
Most of the machining centers can be designed as a dual-workbench exchange. When one workbench runs in the processing area, the other workbench replaces the workpiece outside the processing area to prepare for the next workpiece processing. The time of the workbench exchange depends on the workbench. The size can be completed from a few seconds to tens of seconds.
The newly designed machining center takes into account the structure to be suitable for forming a modular manufacturing cell (FMC) and a flexible production line (FMS ). The modular manufacturing cell generally consists of at least two processing centers and four exchange tables, and the processing centers are all placed side by side , The exchange table is lined up in front of the machine tool, and the exchange table can be arranged in two rows or even double-layer design. There is a workstation on both sides as the position of the upper and lower workpieces. The exchange tables on the other workstations are equipped with workpieces waiting for processing. A trolley will follow the system instructions to send the exchange table with the workpieces to the machining center or from the machining center. Take out the completed processing exchange table and send it to the next station or directly to the unloading station to complete the entire processing operation. In addition to the trolley and the exchange table, the flexible production line also has a unified tool library. Generally there are hundreds of tools. The identification code information of the tools is stored in the system, and then sent to the machining center through the tool conveying system, and used After the tool is retrieved, the flexible production line often needs an FMS controller to direct the operation.
In the past, five-axis machining centers were mostly made in Germany, the United States, Japan, and Italy. What is gratifying is that at the "China CNC Machine Tool Exhibition" held in Shanghai in March this year, a number of domestically produced five-axis machining centers were exhibited. For example, the gantry five-axis machining center exhibited by Jinan No. 2 Machine Tool Group Corporation, the worktable is 6m long, 2m wide, and adopts vertical spindle rotation. The A-axis rotation angle is ±100 degrees, and the C-axis rotation angle is ±200 degrees. This behemoth has attracted many visitors. In addition, it marks that China's CNC machine tool industry has reached an advanced level. The vertical-horizontal machining center manufactured by Shanghai No. 3 Machine Tool Plant and No. 4 Machine Tool Plant, with a worktable of 630mm2, adopts a high-speed internally cooled electric spindle. The three-axis machining center with horizontal conversion can realize pentahedral machining of the workpiece, although it has not been equipped with five-axis, it is also very practical.
The difference between vertical machining center and horizontal machining center:
Obviously because the workbench is bigger, it is changed to the set-up type. Obviously, the vertical type can process larger parts (in fact, all vertical equipment has a larger workpiece size capacity than the corresponding horizontal equipment. This is The natural advantages of vertical equipment.) The main difference between horizontal machining center and vertical machining center is: the main shaft (feed axis) is parallel to the bottom surface and the other is vertical to the ground. The vertical type is obviously vertical to the ground, and the horizontal spindle It is parallel to the ground, the horizontal type is equivalent to a boring machine, but it has many functions and high precision.