CNC Machining and CNC Machine Tools

Some people say that first learn three-axis, and then engage in four-axis and five-axis machining centers. What is the difference between these types of machine tools?

high precision customized continental manufacturing

Some people say that first learn three-axis, and then engage in four-axis and five-axis machining centers. What is the difference between these types of machine tools? high precision customized continental manufacturing
The role and advantages of 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, high-end machining centers are moving towards the direction of five-axis control, and the pentahedron can be processed in one clamping of the workpiece. If equipped with a five-axis linkage high-end numerical control system, it can also perform high-precision processing of complex spatial surfaces. high precision customized continental manufacturing

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Four-axis simultaneous machining

The so-called four-axis linkage machining generally adds a rotation axis, usually called the fourth axis. Generally, the machine tool has only three axes, that is, the workpiece platform can move left and right (1 axis) back and forth (2 axes) and the spindle head (3 axes) 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 losing accuracy in the secondary clamping. high precision customized continental manufacturing

Features of four-axis simultaneous machining:

(1). The three-axis linkage processing machine tool cannot be processed or needs too long clamping

(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 has one more rotation axis and four-axis coordinates are established 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 revolves around the Z axis at the position shown in the figure, which is defined as the C axis, and the C axis 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, etc. 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 spindle is relatively simple, the rigidity of the spindle 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, which can circle 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 also has a 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 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 processing of molds, which is difficult for rotary table machining centers. 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.

X, Y, and Z three linear axes can also use linear grating feedback, and the bidirectional positioning accuracy is within micrometers. Because the rapid feed rate reaches 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 between vertical and horizontal, the worktable can be easily configured as a vertical and horizontal conversion three-axis machining center only by indexing and positioning. The vertical and horizontal conversion of the main shaft cooperates with the indexing of the worktable to realize 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 table. The A-axis of the table mounted 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 during high-speed idling. 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. The first choice for machining. high precision customized continental manufacturing

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 machining centers and four exchange tables, and the machining 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 upper and lower workpieces. The exchange table on the other workstations is equipped with workpieces waiting for processing. A trolley will follow the system instructions to send the exchange table with 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 ID code information of the tools is stored in the system, and then sent to the machining center through the tool conveying system for use. 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 has a worktable of 6m long and 2m wide. It adopts vertical spindle rotation. The A-axis rotation angle is ±100 degrees, and the C-axis rotation angle is ±200 degrees. This giant 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 the Shanghai No. 3 Machine Tool Plant and the No. 4 Machine Tool Plant has a worktable of 630mm2. It adopts a high-speed internally cooled electric spindle. The spindle can be converted from vertical to horizontal. The worktable can be divided into equal parts by 360 degrees. The three-axis machining center with horizontal and 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 establishment 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 advantage 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. It is obvious that the main shaft is vertical to the ground, 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.

high precision customized continental manufacturing
high precision customized continental manufacturing

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