How to advance the cutting technology of five-axis MC to achieve high efficiency and high output
Innovations in production, such as robot-assisted automation on the production floor and remote operation on CNC machine tools, are advancing at a rapid pace. The five-axis machining center (MC) has been on the market for some time, and its effects have been recognized in terms of streamlining processes, reducing cutting time, and improving accuracy, and there is greater flexibility in machining forms, which is expected to promote the integration of parts . These benefits are recognized. On the other hand, the use of five-axis MC in production is limited, which may be due to the fact that tooling and cutting techniques for five-axis MC are not well understood.
On the other hand, NC control systems for five-axis MCs have begun to provide information through network functions, as well as initiatives aimed at improving cutting accuracy and reducing cutting time. For example, on-machine measurement and automatic tool compensation systems have greatly improved cutting accuracy and are changing the perception of 5-axis MC. In the past few years, the development of MC for precision micro-cutting and special-purpose micro-diameter end mills has progressed, and new developments have a good momentum, and many examples of high efficiency and high accuracy continue to appear. This article introduces the cutting technology of five-axis MC using the characteristics of end mills based on the information obtained at the 31st Japan International Machine Tool Exhibition (JIMTOF2022) held in Tokyo Big Sight (Tokyo Ariake) last year, and introduces five-axis MC The latest trends and application examples.
New trend of five-axis MC on JIMTOF2022
JIMTOF2022 was held face-to-face for the first time since 2018, attracting a large number of visitors. Machine tools, cutting tools and other equipment were displayed in the exhibition hall, where initiatives of the information age attracted attention as a new trend. For example, visualization of cutting and production status, automatic generation of NC programs, advanced simulation software, and other examples of real-time situation monitoring and pursuit of high performance are introduced. In particular, competition is starting for the next generation of 5-axis MCs with intelligence and information-oriented functions.
For example, (pic1) shows an example of visualization of a production site on a small 5-axis MC, where information such as tools, production volume, etc. can be displayed on the display screen of the NC controller, which has a network function with the robot and various sensors.
(pic2) shows an example of a 5-axis MC with on-machine measurement and automatic tool compensation, which attracted attention for its high-precision cutting demonstration of a few microns and cut samples with smooth finished surfaces, even the most Faint cut marks.
How to live use Axis MC for 5-axis MC
If 5-axis MC is to be used as the core production equipment, it is necessary to understand the difference in cutting technology between 3-axis control MC and 5-axis MC end mills.
①The end mill has a shorter under-neck length and a tapered shape, which increases the rigidity of the tool and enables higher cutting edge loads under higher cutting conditions.
② Cutting with an end mill with an inclined outer edge can obtain a higher actual cutting speed.
③ Multi-faceted cutting is expected to simplify the production process. In other words, increasing cutting speed is an effective means to improve cutting precision and reduce tool wear, while five-axis MC can cut at high actual cutting speed, which has advantages in improving precision and tool life.
(pic3) shows the pose of the end mill in 5-axis MC. Since the outer edge where the actual cutting speed is high is the cutting point, the inclination angle of each end mill is set. As shown in (pic4), it can be applied to highly rigid end mills with a short neck, tapered shape, and a large number of flutes because of their high accessibility to the workpiece.
Under cutting conditions where the load on the edge (depth of cut and feed rate) and the actual cutting speed increase, especially in cutting where the feed rate increases, high rigidity end mills are expected to be effective in reducing cutting time and tool life. For example, (pic5) shows a comparison of cutting surfaces in a machined profile with large protrusions, chatter occurs in 3-axis MC, while stable cutting can be achieved in 5-axis MC. Therefore, the number of finishing operations is the least during five-axis MC cutting, which makes a big difference in reducing cutting time and improving cutting accuracy.
Square end mills also have many functions, mainly focusing on the cutting of the peripheral edge, but also need to have the cutting function of the bottom edge. In three-axis MC cutting, the tool path is a bevel pattern formed by the leading edge and the trailing edge. Five-axis MC allows the tool to be tilted (pic3), for example to 1°, so that the heel edge does not touch (heal) during cutting. This is beneficial for cutting surface roughness and tool wear. It can be seen that five-axis milling is a completely different milling process from three-axis milling. In addition to cutting efficiency, it also has advantages in tool wear. Next, in order to effectively utilize five-axis MC, the following points must be considered.
1,The construction and application of a single tool database
In order to take full advantage of the characteristics of a dedicated end mill, it is necessary to provide information on the individual tool paths and cutting conditions (minimum and maximum depth of cut, feed rate, cutting speed range, etc.). pic6 shows an example of a tool information system.
2,Tools suitable for shrink-fitting process
Five-axis MC can cut with a fixed tool path and a fixed cutting point of an end mill. The runout accuracy during high-speed rotation has a great influence on cutting accuracy and tool life. In other words, it is more effective to use shrink-fit tools with higher vibration precision at this time.
3,Dedicated CAM and simulation software
For high precision, in-machine measuring systems and automatic tool correction software are available. Measuring the workpiece surface and checking the actual finishing allowance before finishing can achieve higher cutting accuracy. PIC7 shows an example of a system that effectively utilizes on-board measurements and data.
4,Application of special fixtures and separation systems in fully automatic robot-assisted systems.
Future production sites are expected to be automated by robots, which requires special fixtures with highly repeatable workpiece positioning accuracy (see pic8 for example). In the future, it is expected that AI will be used to measure the wear of the cutting edge of a tool, determine tool life, and automatically determine optimal cutting conditions for greater precision.
Environmentally friendly dry and semi-dry cutting
The decarbonization that is already underway globally also calls for coolant-free moves in production. The heat generated when the end mill cuts (cutting heat) exceeds 1,000°C. Cutting heat is conducted to the cutting edge, workpiece cutting surface and chips, but if most of the heat is conducted to the chips, tool wear can be reduced. As we all know, the chip shape is related to the cutting speed, as shown in pic9, as the cutting speed increases, the chip will appear in a wider and thinner shape, and the cutting heat is easy to conduct. In finishing, the supply of mist coolant on the side of the end mill can delay the progress of wear; the five-axis MC can cut at a higher actual cutting speed of the end mill, which is very important for generating chip shapes that are easy to conduct cutting heat is advantageous.
Examples of 5-axis MC cutting and the situation in China
The introduction of 5-axis MC in production facilities is progressing, and new fields are being expanded by cutting utilizing its superiority. On the other hand, the environment surrounding 5-axis MC is far from satisfactory, requiring a trial-and-error approach in tool selection, determination of cutting conditions, and NC programming.
pic10 introduces examples of direct engraving and cutting of gear forging dies (hard steel material) and direct engraving and cutting of endem diamond monuments (hard steel). Both are examples of one-size-fits-all cutting with a dedicated reamer, and cutting with a high-rigidity reamer has higher cutting surface accuracy in addition to cutting time, compared to a three-axis MC. Reducing cutting time is a crucial issue where mold production has emerged by additive manufacturing (AM: printing 3D objects by stacking metal and resin multiple times using sliced 2D data from 3D CAD data) .
Not only in Japan, but also in China, the shift to 5-axis MC is spreading rapidly. Figure 11 shows five-axis MC machines introduced at a recent exhibition in China, all of which are equipped with their own NC controllers, CAM and other software, giving the impression that they are rapidly becoming more complex.
As mentioned above, the condition for achieving efficient cutting with five-axis MC is to utilize the advantages of traditional three-axis control MC in terms of end mills, tool paths and cutting conditions. In addition, by introducing and systematizing on-machine measurements, five-axis MCs have begun to achieve substantial improvements in cutting accuracy. In the future, as part of realizing informatization, it will be an urgent task to deal with and solve issues such as the automation of NC programs, the construction of cutting data for each tool, and the determination of optimal cutting conditions by MC itself based on machining information.
Finally, thanks would be given to all the companies involved for their useful production information and technical data in writing this report.