Comparison of five-axis machine tools with spindle oscillation and table oscillation

The five axes of a five-axis machine tool are usually composed of three linear axes plus two rotary axes, but their structures are very different. Different structural forms will cause some differences in machine tools’ rigidity, dynamic performance, accuracy and stability. This article mainly analyzes and compares two different structures of five-axis machine tools: vertical spindle swing and vertical spindle fixed workbench swing (cradle type), so that users can fully understand their structural forms, which will help them adapt to the characteristics of their own products. Choose the right machine tool according to your financial ability.

Figure. Cradle type rotary table Figure. Spindle rotation and swing

1. Comparison of machine tool spindle rigidity

During the machining process of the head-swing machine tool, due to the swing of the spindle, the rigidity of the spindle is relatively poor; while for the swing-table machine tool, because the worktable swings, it will not have any impact on the rigidity of the spindle.

2. Comparison of efficiency of machine tool processing

Due to the different rotation points, when the tool tip achieves the same displacement, the spindle of the oscillating machine tool needs to swing at a larger angle (similar to the lever principle), so the efficiency of the oscillating machine tool is lower when processing the same parts.

3. The influence of tool length on machine tool machining accuracy

Swing error = swing arm × swing angle

For head-swing machine tools, the tool length is part of the swing arm.

In other words, in the case of head swing, the length of the tool affects the length of the swing arm, amplifying the error. That is, the error will increase with the length of the tool. For cradle table swing machines, the tool length is independent of the length of the swing arm.

4. With the swing, both machine tools will produce position errors, but the head-swing machine will also produce shape errors, while the table swing will not produce shape errors.

The head-swing machine tool tool rotates, resulting in position error. At the same time, the feed direction of the machined hole deviates from the rotation center of the tool, so not only the position error of the machined hole is generated, but also the shape error is generated, resulting in a wedge-shaped hole.

The position error of the table swing machine tool is caused by the table swing. The feed direction of the spindle and the rotation center of the tool always coincide, so there will be no additional shape error. This is another clear advantage of a cradle table swing over a head swing.

5. Comparison of five-axis machining size ranges

As the spindle of the head-swing machine tool swings, the processing range in the diameter direction of the workpiece will be reduced. That is to say, the stroke will be eaten up when the spindle swings, resulting in the diameter range of the largest workpiece that can be processed by five-axis machining than that of three-axis machining. The worktable swing of the worktable swing machine tool will not have any impact on the horizontal size of the workpiece. In this sense, the workpiece size range during five-axis machining and three-axis machining is the same. However, the maximum range of five-axis machining of workpieces still needs to consider the interference caused by the machine tool structure. Users should ask machine tool suppliers to provide five-axis machining interference diagrams for analysis and comparison. Usually, for the same stroke, the five-axis processing range of a machine tool with a cradle-type worktable swing structure will be larger than that of a head-swing type machine tool.

Therefore, the spindle of the cradle-type worktable swing machine tool has good rigidity and high processing efficiency; the tool length will not affect the processing accuracy; the processing will not produce shape errors; for the same stroke, the five-axis processing range of the machine tool will be wider than that of the head-swing type machine tool. big.

The rigidity of the spindle of the head-swing machine tool is relatively poor, and the processing efficiency is relatively low; the processing accuracy will decrease with the growth of the tool length; the processing will produce shape errors; the stroke will be eaten up when the spindle swings angle, resulting in the maximum workpiece size that can be processed become smaller.

In addition, it should be added that the worktable swing machine tool needs to overcome the self-weight of the workpiece. If the workpiece is heavy, it has higher requirements for the fixture; also, when processing large and heavy parts, the machine tool cannot realize the worktable swing, so it can only use The way your head swings.

Vertical and horizontal spindles of five-axis machining centers

There are also two structures for vertical and horizontal spindles. One is to use a 45° inclined plane to convert the spindle vertically or horizontally (Figure 4). Its advantages are a large 45° bevel contact surface, good spindle rigidity, a mouse tooth plate for positioning, high repeatability, and the position of the tool center point remains unchanged after vertical and horizontal conversion, making it easy to program. Of course, its disadvantage is that it has no negative impact angle.

Another form is the A-axis. Its advantage is that it has a large X angle, which is especially suitable for processing large-angle impellers. However, its shortcomings are very obvious. The vertical and horizontal conversion will eat up the Z-axis travel. Generally speaking, the Z axis is the shortest among the X, Y, and Z axes of the machine tool. If it is eaten a little longer, it will greatly reduce the processing range of the machine tool.

Figure 4 Figure 6

Of course, some users hope to achieve clamping without affecting machine tool processing, so double worktables, multi-workstations (FMS), etc. are available as options (Figure 6).

Vertical and horizontal conversion table of five-axis machining center

There are two structures for the vertical and horizontal conversion of the worktable. One is to use a 45° inclined plane for vertical and horizontal conversion and positioning (Figure 1, 2). The advantage is that the 45° inclined plane has a large contact surface, the worktable has good rigidity and load-bearing, and Switching between upright and lying down does not affect the stroke. The positioning surface is not stressed, ensuring high accuracy. The other type is called a cradle-type workbench (Figure 3). Since it uses a shaft-holding method for positioning, the positioning accuracy is poor, and the load-bearing capacity of the workbench is also light. It will receive a large torque during processing, which is a problem for positioning. Unreliable. A lot of travel will be consumed when changing the worktable between upright and horizontal positions. Generally used in economical machining centers.

Rotary axis structure of five-axis machining center

The rotary axis structure plays an important role in the function and performance of the five-axis machining center machine tool. In recent years, its structural development mainly includes the following four aspects:

(1) Use torque motor drive to reduce mechanical transmission and improve dynamic performance, such as CYTE’s CyMill universal milling head;

(2) Develop A/B/C three-axis swing milling heads to make angle changes more flexible and faster, such as the M3A/B/C three-axis swing angle milling head from German Zimmermann Company;

(3) Develop compact A/B double-swing milling heads. For example, the swing angle of the DTH-type A/B double-swing milling head of Italian RAMBAUD1 company has been increased to 45°. In addition, the parallel link mechanism milling head developed by Qi Er Machine Tool Company in my country is suitable for the A/B swing angle of the horizontal axis. It is novel, but the swing angle range is small.

(4) The structure that uses 45° inclined plane rotation to convert the axis vertically or horizontally is generally called the B-axis. Due to the large rotation joint surface, the stiffness and braking torque can be improved. However, when the inclined plane rotates 180°, the axis swing angle is only 90°. , so the swing angle range is smaller, and it is more suitable for occasions where five-sided processing is the main purpose.

Characteristics and Selection of Five-Axis Machining Machine Tools

Whether it is a five-sided processing machine tool or a five-axis linkage processing machine tool, they all add at least two of the three rotary motion axes A, B, and C to the three linear motion axes of X, Y, and Z. This exports various layout plans for five-axis machining machines. The appropriate machine tool structural layout can be determined based on factors such as the shape, size, weight, required accuracy, mechanical properties of the material, and cutting load of the workpiece.

Table 1 lists 10 common layouts based on the three-linear axis structural layout of vertical machining centers and horizontal machining centers configured with different rotary motion types and their applicable applications. There are two types of rotary axis types in the table: the split type means that the tool and the workpiece have one rotary motion axis respectively, while the integrated type means that both rotary axes are configured for the tool or the workpiece, which is often called a double pendulum milling head or a double pendulum turntable.

Number 6 in the table has two double swing turntables, A/C and B/C. Although the working principle is the same, the A/C turntable has left and right supports and is more rigid. However, when the table is turned backwards, due to the narrow space, it is generally difficult to prevent interference. The swing angle is small, while the B/C turntable is usually a single-arm support with less rigidity, but the swing angle range is large and easy to observe, so it is suitable for processing small parts.

Vertical and horizontal conversion table of five-axis machining center

There are two structures for the vertical and horizontal conversion of the worktable. One is to use a 45° inclined plane for vertical and horizontal conversion and positioning (Figure 1, 2). The advantage is that the 45° inclined plane has a large contact surface, the worktable has good rigidity and load-bearing, and Switching between upright and lying down does not affect the stroke. The positioning surface is not stressed, ensuring high accuracy. The other type is called a cradle-type workbench (Figure 3). Since it uses a shaft-holding method for positioning, the positioning accuracy is poor, and the load-bearing capacity of the workbench is also light. It will receive a large torque during processing, which is a problem for positioning. Unreliable. A lot of travel will be consumed when changing the worktable between upright and horizontal positions. Generally used in economical machining centers.

Rotary axis structure of five-axis machining center

The rotary axis structure plays an important role in the function and performance of the five-axis machining center machine tool. In recent years, its structural development mainly includes the following four aspects:

(1) Use torque motor drive to reduce mechanical transmission and improve dynamic performance, such as CYTE’s CyMill universal milling head;

(2) Develop A/B/C three-axis swing milling heads to make angle changes more flexible and faster, such as the M3A/B/C three-axis swing angle milling head from German Zimmermann Company;

(3) Develop compact A/B double-swing milling heads. For example, the swing angle of the DTH-type A/B double-swing milling head of Italian RAMBAUD1 company has been increased to 45°. In addition, the parallel link mechanism milling head developed by Qi Er Machine Tool Company in my country is suitable for the A/B swing angle of the horizontal axis. It is novel, but the swing angle range is small.

(4) The structure that uses 45° inclined plane rotation to convert the axis vertically or horizontally is generally called the B-axis. Due to the large rotation joint surface, the stiffness and braking torque can be improved. However, when the inclined plane rotates 180°, the axis swing angle is only 90°. , so the swing angle range is smaller, and it is more suitable for occasions where five-sided processing is the main purpose.

Characteristics and Selection of Five-Axis Machining Machine Tools

Whether it is a five-side processing machine tool or a five-axis linkage processing machine tool, they all add at least two of the three rotary motion axes A, B, and C to the three linear motion axes of X, Y, and Z. This exports various layout plans for five-axis machining machines. The appropriate machine tool structural layout can be determined based on factors such as the shape, size, weight, required accuracy, mechanical properties of the material, and cutting load of the workpiece.

Table 1 lists 10 common layouts based on the three-linear axis structural layout of vertical machining centers and horizontal machining centers configured with different rotary motion types and their applicable applications. There are two types of rotary axis types in the table: the split type means that the tool and the workpiece have one rotary motion axis respectively, while the integrated type means that both rotary axes are configured for the tool or the workpiece, which is often called a double pendulum milling head or a double pendulum turntable.

Number 6 in the table has two double swing turntables, A/C and B/C. Although the working principle is the same, the A/C turntable has left and right supports and is more rigid. However, when the table is turned backwards, due to the narrow space, it is generally difficult to prevent interference. The swing angle is small, while the B/C turntable is usually a single-arm support with less rigidity, but the swing angle range is large and easy to observe, so it is suitable for processing small parts.

Horizontal five-axis machining center

The rotary axis of this type of machining center also has two methods. One is that the horizontal spindle swings as a rotary axis, coupled with a rotary axis of the workbench, to achieve five-axis linkage processing. This setting method is simple and flexible. If the spindle needs to be switched vertically and horizontally, the worktable only needs to be indexed and positioned, and it can be simply configured as a three-axis machining center with vertical or horizontal switching. The vertical and horizontal conversion of the spindle and the indexing of the worktable enable pentahedral processing of the workpiece, which reduces manufacturing costs and is very practical. The worktable can also be equipped with CNC axes, with a minimum indexing value of 0.001 degrees, but without linkage, to become a four-axis machining center that converts vertically and horizontally, adapting to different processing requirements, and the price is very competitive.

The other is the traditional workbench rotary axis. The A-axis of the workbench set on the bed generally has a working range of +20 degrees to -100 degrees. There is also a B-axis of the turntable in the middle of the workbench, and the B-axis can rotate 360 degrees in both directions. The linkage characteristics of this horizontal five-axis machining center are better than the first method, and it is often used to process complex curved surfaces of large impellers. The rotary axis can also be equipped with circular grating feedback, and the indexing accuracy can reach a few seconds. Of course, the structure of this rotary axis is relatively complex and the price is expensive.

At present, the horizontal machining center worktable can be larger than 1.25m2, which has no impact on the first five-axis setting method. However, the second five-axis setting method is more difficult, because it is really difficult for a 1.25m2 workbench to rotate the A-axis and link it with the B-axis rotary table in the middle of the workbench. The spindle speed of a horizontal machining center is generally above 10,000 rpm. Since the horizontal spindle has its own gravity in the radial direction, the radial force on the bearings is uneven when running dry at high speed. In addition, a larger BT50 tool holder must be used. Generally up to 20,000rpm. The horizontal machining center has a rapid feed rate of more than 30-60m/min, a spindle motor power of more than 22-40KW, and a tool magazine capacity that can be increased from 40 to 160 as needed. The processing capacity far exceeds that of ordinary vertical machining centers. It is a heavy-duty machining center. The first choice for machining.

Most machining centers can be designed with double workbench exchange. When one workbench is running in the processing area, the other workbench changes workpieces outside the processing area to prepare for the processing of the next workpiece. The time of workbench exchange depends on the workbench. The size can be completed from a few seconds to tens of seconds. The latest designed machining center is structurally suitable for forming a modular manufacturing cell (FMC) and a flexible production line (FMS). The modular manufacturing unit generally consists of at least two machining centers and four exchange workbenches. The machining centers are all placed side by side. , the exchange workbench is arranged in a line in front of the machine tool. If there are many exchange workbench, it can be arranged in two rows or even a double-layer design. There is a station on each side as the location for the upper and lower workpieces. The exchange workbench on the other stations is equipped with workpieces waiting to be processed. A small car will follow the system instructions to send the exchange workbench containing the workpieces to the machining center, or from the machining center. Take out the exchange workbench that has been processed 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 exchange workbench, the flexible production line also has a unified tool library. There are usually hundreds of tools. The identity code information of the tools is stored in the system, and then sent to the machining center through the tool delivery system, and the tools are used. After completing the tool retrieval, the flexible production line often requires an FMS controller to direct the operation.

small_c_popup.png

Let's have a chat

Leave your information, our sales will contact you as soon as possible!