5-axis linkage CNC machine tools play a vital role in a country’s overall industrial manufacturing capabilities and even national defense security.
At this point, we have to talk about the famous Toshiba–Kongsberg scandal.
Toshiba–Kongsberg scandal
During the Cold War, the Soviet Union lagged behind Western countries in defense technology, particularly in its submarine fleet, where underwater noise remained a major unresolved issue. The excessive noise was mainly due to poor design and outdated manufacturing techniques.
Lacking high-precision 5-axis machining equipment, the Soviets were unable to produce high-quality propellers with the low geometric tolerances and smooth surfaces needed to reduce noise.
To address this, Soviet defense leaders were determined to acquire advanced Western technology.
In 1980, the Soviet Union was facing a production crisis in agricultural and consumer goods and needed to import machinery to boost output.
Meanwhile, Japan’s Toshiba Machine Company learned during a government banquet in Moscow that the Soviets were seeking CNC machines to manufacture large ship propellers.
Toshiba seized the opportunity and agreed to sell four state-of-the-art MBP-110S 5-axis CNC machines to the Soviets for 3.5 billion yen.
Between 1982 and 1983, the machines were shipped to the northern Soviet naval port of Leningrad and installed at the Baltic Shipyard.
In 1984, Japan and the Soviet Union signed another agreement for spare parts, including 12 milling heads and various components, along with system upgrades for additional processing functions.
Soon after, American intelligence noticed a sharp decrease in Soviet submarine noise, making them harder to track—even when nearby.
The situation came to light in 1986 after a collision between American and Soviet submarines. Following an investigation and a whistleblower report by Toshiba employee Kazuo Kumagai, the full story was exposed.
The United States was outraged, the European Union imposed sanctions, and several Toshiba Machine executives were imprisoned.
This incident shows that all countries are very sensitive to and attach great importance to high-end CNC machine tool technology.
Overview of 5-axis CNC machine tools
In the past, when 5-axis machine tools were not available, multiple sets of fixtures were designed. These fixtures were used for multiple installations, positioning, and locking.
Several 3-axis machining operations were then performed to mill the multi-face structure.
This processing method greatly extended the machining time and significantly reduced the machining quality.
Until modern times, precision CNC machining has become increasingly common.
The realization of precision machining of high-grade CNC machine tools, molds at the forefront of the manufacturing industry chain, and mold product quality is largely limited by CNC equipment.
In the fierce competition in the market, the manufacturing industry requires a shorter production cycle, higher processing quality and faster product re-modeling capabilities and lower manufacturing costs.
To meet these demands, more and more manufacturing companies are adopting high-end 5-axis CNC machining centers.
5-Axis CNC machine tools can be categorized into two main types according to the positional relationship of the spindles.
Vertical 5-axis CNC Linkage Machines
Principles and Applications
These machining centers with rotary table are set up on the bed with a table that rotates around the X-axis, defined as the A-axis, which has a general operating range of +30° to -120°.
In the center of the table there is also a rotary table that rotates around the Z-axis, defined as the C-axis, which rotates through ±360°.
Thus, by combining the A-axis and the C-axis, the workpiece fixed on the table can be machined by the vertical spindle on all 5 sides except the bottom side.
Fine Indexing and Complex Spatial Surface Machining Capabilities
The A-axis and C-axis have a minimum indexing value of 0.001°, which allows the workpiece to be subdivided into any angle, and features such as inclined surfaces and inclined holes can be machined.
If the A-axis and C-axis are linked with the three linear axes X, Y and Z, complex spatial surfaces can be machined, which of course requires the support of a high-grade CNC system, servo system and software.
Advantages and Limitations of Vertical 5-Axis Machining Centers
The advantage of this setup is that the structure of the spindle is relatively simple, the spindle rigidity is very good, the manufacturing cost is relatively low, but generally the table can not be designed too large, the load-bearing is also small, especially when the A-axis rotary is greater than or equal to 90 °, the workpiece cutting will be brought to the table with a lot of load-bearing moment.
Alternative Designs for Vertical Spindlehead Rotation
The other is to rely on the vertical spindle head rotation. At the front of the spindle is a rotary head that can rotate 360° around the Z-axis by itself, called the C-axis, and the rotary head also has an A-axis that can rotate around the X-axis, generally up to ±90° or more, to realize the same function as above.
The advantage of this setup is that the spindle is very flexible and the table can be designed to be very large, which makes it suitable for machining automobile bodies, large engines, and so on.
CNC Horizontal 5-Axis Machining Center
The traditional table rotary axis type 5-axis machining center, the table A-axis which is set on the bed generally has a working range of +20°~-100°.
In the center of the table, there is also a rotary table B-axis, which can rotate 360° in both directions.
This horizontal 5-axis machining center has good linkage characteristics and is often used for machining complex surfaces of large impellers.
The rotary axis can also be equipped with rotary scale feedback, high indexing accuracy, but of course, the structure of this rotary axis is more complex and expensive.
Functions and Features of 5-axis CNC Machining
Machining Complex Free-form Surfaces
It can machine products that cannot be processed by 3-axis CNC machines. These include the blades of aero-engines and turbines, as well as screw propellers used in ships.
Additionally, it can handle many housings and molds that have special surfaces, complex cavities, and holes.
Shorter tools can be used to machine deep and long cavity parts and convex mold parts with high and steep walls
In the process of parts machining, the longer the tool is used, the greater the amount of tool axis deflection.
This deflection can easily lead to undercutting of convex molds and overcutting of concave molds. As a result, the quality of parts machining will be significantly reduced.
For stepped parts, on a 3-axis machine, a tool with a long enough shank and cutting edge must be used to cut the part.
With a 5-axis machine it is possible to machine the same object with a long deep cavity or high steep-walled surfaces using short tools by oscillating the angle of the tool axis.
Necessary Technology for Machining Large Samples
When machining large parts such as automobile mold plates and large wind turbine blades, 5-axis CNC machines must be used to machine such features as large variations in the shape of the sidewalls of the mold plates.
The side of the car model is not a simple flat surface; it has irregular and varying structural features.
Using 3-axis machine tools is not sufficient to fully process these surfaces. Instead, 5-axis linkage CNC machine tools must be used.
The angle of the tool and the workpiece must be adjusted during the cutting and processing to achieve the desired result.
Effectively improve the cutting accuracy and surface quality of complex surfaces
3-axis CNC machine tools use semi-circular ball milling cutters for processing complex surfaces.
However, the cutting efficiency at the vertex part of the ball milling cutter is extremely low, almost approaching zero.
Additionally, the angle between the workpiece and the 3-axis CNC machine tool is not adjustable, further limiting cutting efficiency.
Therefore, it is difficult to utilize the optimal cutting point on the ball-end milling cutter during machining. As a result, the cutting often occurs at the apex of the ball-end milling cutter.
This situation is referred to as “zero-point cutting,” where the machining surface and the contact cutting point coincide at the tip of the tool.
As shown in Figure 1, Figure 2, can clearly see the ball milling cutter and the workpiece surface contact point changes.
Zero-point cutting not only leads to a slow cutting speed but also results in a poor surface finish of the workpiece.
As a consequence, manual surface repair is often required, such as polishing or sanding.
These additional steps cause the workpiece to lose its original surface quality.
As a result, the surface of the workpiece can lose its original machining accuracy.
However, 5-axis machine tools do not have this problem. During the cutting process, the angle of the tool can be adjusted at any time.
This ensures that the optimal cutting condition between the tool and the workpiece is consistently maintained.
As shown in Figure 2, not only can we obtain higher machining speed and side draft, but also greatly improve the machining efficiency and speed, more perfect surface and finish.
Bring higher machining efficiency for mold products processing
The advantages of 5-axis machining are especially evident in side milling operations involving angular surfaces.
For tapered parts, using a 5-axis machine tool allows the use of a cylindrical end mill instead of a ball-end mill.
This not only greatly improves machining efficiency, but also eliminates the mesh-like cutter pattern typically left by ball-end milling.
As a result, the best possible surface quality can be achieved.
Effective Improvement of Tool Use Time
5-axis machining improves tool usage time by allowing changes to the cutting surface of the tool. At the same time, using high-speed machining centers results in faster cutting efficiency and shorter machining times.
However, tool wear typically occurs only at the tip of the tool. This shortens the effective usage time of the tool and requires the tool to be resharpened before it can be used again.
With 5-axis machines, however, the tool is more often used to cut on the side of the tool in addition to the tip, maximizing utilization and therefore increasing overall tool life.
Applications of 5-axis CNC machining
Although there are still some difficulties in the generalization of 5-axis machining machines, multi-axis CNC machining technology has been commonly used in some areas of the processing industry to manufacture products.
Applications in Mold Manufacturing
5-axis machining applications in mold manufacturing mainly include plate machining, concave and convex molds, and deep holes or cores.
Features such as grooves, chamfered corners, steep walls, and beveled holes are also machined.
These features allow the full advantages of 5-axis machining to be utilized.
For example, molds often have excessively deep mold cavities, high mold cores, and small internal R angles.
A common solution in this case is to use an extension bar. This reduces the amount of cutting and speeds up machining, but it results in low efficiency and poor quality.
Traditionally, several methods have been used to address structures that cannot be machined on a 3-axis machine.
These include splitting the part into smaller, machinable sections, machining the parts in pieces, or designing specialized fixtures based on the part’s structure. In some cases, EDM machines are used for processing deep cavities.
However, these approaches can negatively affect both the quality and efficiency of the machining process.
The use of 5-axis machine tilting tool axis machining, not only can be processed out of the whole mold, but also significantly improve the quality and efficiency of product processing.
Applied to the processing of product models
To develop a new set of products, the initial requirement is to process the samples in a short time to assess the rationality of their appearance and structure, so as to facilitate timely modification and adjustment.
Model machining requires speed and efficiency, using 5-axis machine tools to machine products will avoid spending many man-hours to turn the model and positioning and other actions, thus improving the efficiency of sample machining.
Aeronautical and Spacecraft Parts Processing
Due to functional and structural requirements, many aeronautical and spacecraft parts are frame parts.
The blanks of these parts are generally forgings with three-dimensional surface features and more thin-walled reinforcing structures, which cannot be processed on 3-axis machines.
Cylinder and seat machining
Engine cylinders have a complex internal structure, and some of the cylinder bores have a curved radius, making it impossible to use 3-axis machining for finishing.
Therefore, cylinder bores are generally machined using 5-axis machines.
Similar to cylinder parts, seat parts often have complex internal structures and features such as side holes and slots, which can be machined using 5-axis machines to reduce the number of fixtures.
The use of a 5-axis machine can reduce the number of fixtures, reduce the number of fixtures, reduce the number of hours of work for fixturing and positioning, and improve machining efficiency and quality.
Analysis of the impeller
Principle of operation of the impeller
The impeller is the most important component in an aviation jet engine and is widely used in aerospace and other fields.
Processing the overall impeller requires a solid understanding of its structure, manufacturing process, and related knowledge.
The impeller is one of the most critical and commonly used components in compressed air systems.
During high-speed operation, the impeller compresses a large volume of outside air and delivers it into the engine’s internal chamber.
This process involves continuous air compression, which places high demands on the impeller’s performance and durability.
And by the high-speed operation of the blade under the force of the engine studio internal pressure rises rapidly, the most mixed into the fuel and ignition release energy process.
Therefore, the requirements of the impeller:
First, the loss of gas flow through the impeller should be small;
Second, the impeller type should be able to make the overall performance stability, working condition area and torque range should be wide.
Structural characteristics of the impeller
The main feature of the impeller is that it consists of twisted banded sheets, and there is a lot of material to be removed between the twisted sheets.
In order to achieve maximum aerodynamic performance, the impeller blades are often designed with large torsion angles. To enhance structural rigidity, the bottom of the blades typically features rounded corners.
These design features significantly increase the difficulty of impeller machining.
The processing difficulties mainly arise from several structural characteristics of the part. The blade duct transitions from large to small, and the blades themselves are thin and long, resulting in unstable rigidity.
As the component falls under the category of sheet parts, it is highly susceptible to deformation or breakage during machining.
Additionally, the narrow and distorted space between blades complicates the process further.
Machining the rounded corners at the bottom requires tools with a small diameter, and ball-end cutting tools, though commonly used, are more likely to break under these conditions.
Severe blade distortion increases the risk of interference during machining, making the overall process extremely challenging, as illustrated in Figure 3.
According to the geometric structure characteristics of the impeller and the use of requirements, to determine the basic processing technology flow:
selection of aluminum alloy materials; processing of the basic shape;
rough machining of the blade hub; blade hub finish machining;
rough machining of the runner;
finish machining of the hub surface;
blade finish machining.
Programming steps and results of the impeller
UG NX8.0 is currently one of the advanced computer-aided design, analysis and manufacturing software, widely used in aviation, aerospace, machinery and other fields. In this paper to UG8.0 to write the program, the steps are as follows:
(1) Setting Up Machine Tool Coordinate System and Part Geometry in UG8.0
As noted in the size of the impeller, in UG8.0 to create a good machine tool coordinate system, set up the blank geometry, and specify the part.
(2) Tool Selection for Milling Program Creation
According to the graphics were created in accordance with the tool ϕ10mm flat and low milling cutter, ϕ10mm flat and low milling cutter, ϕ8R4mm ball head cutter, ϕ8R4mm ball head cutter.
(3) Cavity Milling Program for Leaf Hub Roughing and Contouring
Create the cavity milling program, use ϕ10mm flat and low milling cutter to designate the cutting area to rough the leaf hub, and use ϕ10mm flat and low milling cutter to finish the outer contour and the plane.
(4) Create a contour area program and use ϕ8R4mm ball end cutter to finish the leaf hub.
(5) Create a multi-blade geometry, specifying the hub, wrap, blade, and root fillet.
(6) Multi-Blade Roughing Program for Runner Using Ball-End Cutter
Create a multi-blade roughing program to rough the runner with a ϕ8R4mm ball-end cutter, and set the cutting layer, the inward and outward cutting parameters, as well as the feed rate and the spindle speed, respectively.
The simulation machining results are shown in Fig. 4, and the actual machining results are shown in Fig. 5.
(7) Leaf Hub Finishing Program with Ball End Cutter
Create the leaf hub finishing program, use ϕ8R4mm ball end cutter to finish the runner, and set the cutting parameters, forward and backward cutting parameters, as well as the feed rate and spindle speed respectively.
The simulation machining results are shown in Fig. 6, and the actual machining results are shown in Fig. 7.
(8) Blade Finishing Program Using Ball End Cutter
Create blade finishing program, use ϕ8R4mm ball end cutter to finish the blade, set cutting layer, in/out cutting parameters, feed rate and spindle speed respectively.
The simulation machining results are shown in Fig. 8, and the actual machining results are shown in Fig. 9.
(9)Variable Flow Milling Program for Impeller Cutting and Chamfering
Create a variable flow milling program, cut off the impeller and chamfer with ϕ10mm milling cutter, set the cutting parameters, forward and backward cutting parameters, as well as the feed rate and the spindle speed respectively.
The simulated machining results are shown in Fig. 10, and the actual machining results are shown in Fig. 11.
Tool table
The tool table is shown in Table 1.
Machining program
%
N0010 G40 G17 G49 G80 G90
N0020 G91 G28 Z0.0
N0030 T02 M06
(D=8.00 R=4.00 F=50.00 L=75.00)
N0040 G00 G90 X-26.1285 Y3.0503 A0.0 C0.0 S15000 M03
N0050 G43 Z9.9998 H02
N0060 Z2.0003
N0070 G01 Z-.1028 F5000. M08
N0080 X-26.127 Y3.0158 Z-.6255
N0440 G03 X-12.6818 Y-22.6965 I14.2245 J21.0908
N0450 G01 X- 12.2633 Y-22.926
N0460 G03 X-9.9802 Y-24.0083 I12.3015 J23.0048
N0470 G01 X-9.3818 Y-24.2483 Z-4.101
Most of the 5-axis program is omitted due to its overkill
… …
N6690 X12.3128 Y24.6885 Z-9.9885 A-43.604 C-77.179
N6700 X10.7513 Y24.171 Z-8.523 A-44.502 C-77.139
N6710 X9.2933 Y23.559 Z-7.1918 A- 45.31 C-77.018 45.31 C-77.086
N6900 Y4.6553 Z8.4653
N6910 X-6.8588 Y4.5758 Z8.604
N6920 X-6.8835 Y4.518 Z8.7622
N7020 G91 G28 Z0.0
N7030 M01
N7040 M30
%
Summary of the problem
In the actual processing of the blade, the overcutting phenomenon occurs. Software analysis reveals that the tool axis is affected by the impeller intake runner, which is narrower.
Additionally, the blade is relatively long. The interference between the red tool part and the blade causes the overcutting phenomenon, as shown in Figure 12.
By modifying and adjusting the angle of the tool axis, the interference phenomenon is corrected, and no interference phenomenon occurs after careful examination.
After modifying the dialog box as shown in Fig. 13, the result is shown in Fig. 14.
Fig. 13 Multi-blade Roughing Dialog Box
When writing the program, pay attention to the range of the rotation angle of the 4th axis (i.e., the A-axis), if the angle is out of the range, collision accidents or machine tool alarm messages will occur.
Conclusion
Compared to older 3-axis methods, 5-axis machines reduce production time, enhance quality, and enable the processing of complex components in a single setup.
5-axis technology is crucial for industries like aerospace, automotive, and mold manufacturing, offering advantages such as the ability to machine steep walls, intricate cavities, and free-form surfaces.
It also improves tool efficiency, surface finish, and allows for better handling of large or complicated workpieces.
The historical Toshiba–Kongsberg scandal underscores the geopolitical importance of advanced CNC technology.
In practical applications like impeller machining, 5-axis machines solve challenges like overcutting by adjusting tool axes, ensuring higher precision.
Overall, 5-axis CNC machining is essential for producing high-quality components with reduced cycle times, making it an indispensable tool in modern manufacturing.