Research and development of high-speed cutting technology

Cutting is a widely used processing method in the current mechanical manufacturing field. Improving cutting efficiency and reducing production costs are of great practical significance to promoting national economy and national defense construction. With the popularization and development of CNC automation technology and high-speed cutting, the auxiliary time of workpiece processing has been greatly shortened, and the proportion of time occupied by cutting processing has increased accordingly (the total working time of part processing is composed of auxiliary time and cutting processing time).

Therefore, to further improve processing efficiency, it is necessary to reduce cutting time. The main way to reduce cutting time is to increase cutting speed and cutting depth. However, with the continuous development of precision manufacturing, the prospect of large margin cutting by increasing cutting depth has been limited. High-speed cutting can not only reduce cutting time, but also reduce cutting force and improve the processing accuracy of workpiece surface. It has been widely used and verified in aerospace, defense industry, electronics and precision machinery industries.

Therefore, high-speed cutting technology has become one of the important research topics in the field of advanced manufacturing at home and abroad. This paper studies the characteristics and applications of high-speed cutting technology, high-speed cutting mechanism, high-speed machine tool and tool technology, and high-speed cutting process and other key technologies, and predicts its future development direction, in order to provide reference suggestions for the development of China’s high-speed cutting technology.

Overview of high-speed cutting technology

 

German physicist Carl J. Salomon first proposed the concept of “high-speed cutting”. His core idea is that each material has a corresponding critical cutting speed. When the cutting speed is lower than this critical value, the cutting force and cutting temperature will increase with the increase of speed; once the speed exceeds the critical value, the cutting force and cutting temperature will decrease with the increase of speed. Therefore, high-speed cutting can not only reduce processing time, but also reduce cutting temperature, reduce tool wear, and improve the surface quality of workpieces.

At present, there is no unified definition of the speed of high-speed cutting. There are usually two ways of classification: one is to define the situation of more than 5 times the conventional cutting speed as high-speed cutting according to the cutting speed; the other is to define the situation of speed exceeding 8000 rpm according to the spindle speed. In actual production, the speed of high-speed cutting is also closely related to the workpiece material and processing method, so it is difficult to give an accurate speed definition.

It is worth noting that high-speed cutting is not just about increasing the cutting speed. It is a complex system engineering that integrates high-speed cutting mechanism, key equipment technology of high-speed cutting, high-speed cutting process and other aspects. With the development of related technologies, high-speed cutting continues to pursue the organic unity of technological progress and benefits.

Advantages of high-speed cutting technology

 

1.Improve production efficiency: High-speed cutting greatly shortens processing time, is suitable for mass production, and improves overall production efficiency.

2.Enhanced machining accuracy: The cutting force is small, the workpiece is less deformed, high-precision machining can be achieved, and the dimensional accuracy and surface quality of the parts are improved.

3.Extend tool life: The cutting temperature is lower and tool wear is reduced, significantly extending the tool life.

4.Improve surface quality: The surface roughness of the processed workpiece is low, reducing the need for subsequent polishing and finishing.

5.Reduce workpiece deformation: Due to reduced cutting force and heat, the workpiece deforms less during processing, and is suitable for processing thin-walled and complex-shaped parts.

6.Wide material adaptability: suitable for various materials, including difficult-to-process materials, such as titanium alloy, stainless steel, etc.

7.Reduce production costs: By improving cutting efficiency and extending tool life, the overall production cost can be effectively reduced.

Application of high-speed cutting technology

 

1. Aerospace

 

· Processing aircraft structural parts and engine components requires high precision and high strength.
· Especially outstanding in the processing of light alloys (such as aluminum alloys and titanium alloys).

2. Automobile manufacturing

 

· Manufacture key components such as engine cylinders and gearbox housings.
· Improve processing efficiency, shorten production cycles, and meet mass production needs.

3. Electronics industry

 

· Process the shells and internal parts of electronic products such as mobile phones and computers.
· Achieve high-precision processing to meet the needs of small-sized and complex-shaped parts.

4. Mold manufacturing

 

· Make precision molds such as injection molds and stamping molds.
· Improve mold processing accuracy and surface quality and extend mold service life.

5. Medical devices

 

· Process medical equipment and instruments, such as artificial joints, implants, etc.
· Meet high precision and high surface quality requirements.

6. Defense industry

 

· Manufacture parts for weapons and military vehicles.
· Improve the processing accuracy and reliability of key parts.

7. Mold manufacturing

 

· Manufacture plastic and metal molds, suitable for mold processing with high precision and high surface quality requirements.
·Shorten the mold manufacturing cycle and increase the mold service life.

In short, high-speed cutting technology is widely used in various manufacturing fields with its advantages of high efficiency, high precision and low cutting force, which has promoted the rapid development of modern manufacturing industry. With the continuous advancement of technology, high-speed cutting technology will show its unique advantages in more fields.

Research on key technologies of high-speed cutting

 

1. Research on high-speed cutting mechanism

 

The high-speed cutting mechanism is the core and foundation of high-speed cutting technology, and plays a guiding and controlling role in the entire high-speed cutting process. Its main differences from traditional ordinary cutting mechanisms are in cutting principles, cutting heat and temperature, and chip formation. The mechanism of high-speed cutting is as follows:

·Cutting principle: In high-speed cutting, as the cutting speed of the tool increases, the cutting force and cutting temperature also increase. When the cutting speed exceeds the critical cutting speed of the material, the cutting force and cutting temperature will decrease, and the cutting efficiency will increase.

·Cutting heat and temperature: The increase in cutting speed leads to the accumulation of cutting heat, and the high-temperature area appears in the contact area between the tool and the workpiece. Part of the material is in a molten state, which plays a lubricating role, reduces the friction coefficient, and reduces the cutting force.

·Chip formation: Under high-speed cutting, the chips produced during the cutting process are serrated, which is a manifestation of the mechanical instability of the material. This chip morphology causes the cutting force and cutting temperature to change periodically, affecting the stability of the entire cutting process and the processing effect.

·Mechanism of serrated chip formation: There is an adiabatic shear theory based on thermal-mechanical coupling and a periodic brittle fracture theory based on dynamic force. The former believes that serrated chips are caused by thermoplastic instability due to the thermal softening effect exceeding the strain hardening effect, and the latter believes that it is caused by periodic fracture.

In general, the study of high-speed cutting mechanism covers cutting principle, cutting heat and temperature, chip formation mechanism and other aspects. It is necessary to comprehensively apply knowledge of heat transfer, fracture mechanics, etc. to explain and explore the complex mechanism in the high-speed cutting process. The understanding of the formation mechanism of serrated chips still needs further research and exploration to improve the understanding and control level of the high-speed cutting process.

2. Research on key equipment technology for high-speed cutting

 

2.1 High-speed cutting machine tools

 

High-speed cutting machine tools are the basic core equipment for high-speed cutting processing, including spindle systems, rapid feed systems and CNC control systems.

The high-speed spindle system is one of the key technologies and must meet the following performance requirements: compact structure, good start-stop performance; high speed and wide speed range; high rigidity and high rotation accuracy; good thermal stability; advanced and reliable lubrication and cooling systems; stable monitoring feedback system.

To meet these requirements, high-speed spindles usually adopt the form of electric spindles, that is, the motor and spindle are combined into one, and the internal structure is directly driven by AC servo motors.

High-speed spindles must be used with rapid feed systems. The feed mechanism of the traditional ball screw nut pair has low transmission efficiency and cannot meet performance requirements.

To meet the requirements of high-speed precision, the guide rail adopts a linear structure with embedded ball bearings, small contact area and low friction; the feed mechanism can adopt high-quality small-pitch ball screws, and the motor can adopt advanced high-speed linear motors. These technologies can achieve high feed speeds and accelerations and improve transmission accuracy.

In high-speed cutting, the CNC control system must also have the functions of fast data processing, forward-looking calculation control, geometric compensation and thermal compensation.

The traditional CAD data conversion into point-to-point tool path trajectory can no longer meet the requirements, and contour control technologies such as NURBS interpolation, smooth interpolation, bell-shaped acceleration and deceleration can be used to improve performance.

2.2 High-speed cutting tools

 

The importance of high-speed cutting tools lies in meeting the requirements of modern high-speed machining technology, and they have the characteristics of high precision, high efficiency, high reliability and specialization. The material, coating and structure of the tool are the key to achieving these characteristics. The selection of tool materials and coatings is of great significance to the development of high-speed cutting technology.

Common high-speed cutting tool materials and coatings include: TiCN-based carbide tools, ceramic tools, diamond tools, PCBN (artificial cubic boron nitride) tools, etc. They each have the characteristics of being suitable for different materials.

For example, TiCN-based carbide tools and ceramic tools are suitable for high-speed machining of steel and its alloys, diamond tools are suitable for high-speed machining of aluminum alloys, titanium alloys, copper alloys and other materials, and PCBN tools are suitable for high-speed machining of high-temperature alloy materials.

The structural parameters of the tool directly affect the tool life and processing quality.

Compared with traditional tools, high-speed cutting tools have smaller rake angles and larger back angles. The increase in the tip angle and the length of the cutting edge can improve the rigidity of the tool and reduce wear.

In addition, under high-speed rotation, the tool structure must meet the requirements of balance quality, and the tool holder device also needs to maintain sufficient clamping force and safety and reliability.

At present, in order to meet the requirements of high-speed cutting, the positioning accuracy and connection rigidity of the tool holder have also been improved, such as Japan’s BIG-PLUS series and Germany’s HSK series.

The traditional solid BT tool holder has low positioning accuracy and insufficient connection rigidity, which cannot meet the needs of high-speed cutting.

Therefore, a close-fitting tool holder that is simultaneously positioned with the spindle inner hole cone and end face has been developed.

2.3 Research on high-speed cutting technology

 

High-speed cutting technology is very different from traditional ordinary processing technology. The design principle of high-speed cutting technology is to give full play to the advantages of high-speed cutting and design a reasonable process plan to achieve high efficiency and high quality.

The research on high-speed cutting technology mainly includes the selection of cutting method, cutting amount and tool feeding method.

In high-speed cutting, down milling is the first choice. In down milling, the cutting thickness changes from large to small, the sliding distance of the cutter teeth on the cutting surface is small, the distance traveled is short, and the smoothness of the workpiece surface is good.

In reverse milling, the cutting thickness changes from small to large, the friction between the tool and the workpiece increases, the radial force also increases greatly, and a large amount of heat is generated at the blade, causing the tool to wear easily.

In high-speed cutting, when different tools cut workpieces of different materials, the selection of cutting amount is also different.

However, the selection principle of high-speed milling cutting amount is generally a medium feed per tooth, a small axial cutting depth and an appropriately large radial cutting depth.

The selection of tool feeding method mainly includes the optimization of tool feeding direction, the optimization of tool feeding path and flexible acceleration and deceleration.

The optimization of tool feeding direction should be evaluated based on the flatness of the surface. The optimization principle of the tool path is simple and smooth, and the interference area can be processed by arc transition.

For flexible acceleration and deceleration, the appropriate acceleration and deceleration method should be selected to reduce the start-stop impact and ensure the processing accuracy of the machine tool.

Prospects of high-speed cutting technology

 

1. Strengthen in-depth research on high-speed cutting mechanism

 

In terms of the theory of high-speed cutting, although a lot of research has been conducted at home and abroad, and some research results have been achieved, it is generally unable to meet the needs of production practice, and further in-depth research is needed..

In-depth research on high-speed cutting mechanism can be strengthened from the following aspects:

1) Digital description and prediction of cutting force and cutting heat distribution law;

2) Research on chip formation mechanism of difficult-to-cut materials, composite materials, and micro-cutting;

3) Description of tool-chip interface tribological behavior and tool wear mechanism;

4) Monitoring and prediction of tool life;

5) Time domain and frequency domain modeling analysis of cutting dynamics.

2. Research on new tool materials and structural technologies

 

The research on new tool materials and structural technologies involves many aspects, including material selection, tool structure design, and processing technology.

Among them, new tool materials may include high-hardness ceramic materials, wear-resistant coating materials, high-strength metal materials, etc. The selection of these materials is closely related to the specific use of the tool.

Tool structure technology includes blade design, blade structure, tool fixing method, etc., aiming to improve the stability, cutting efficiency and life of the tool.

Research on processing technology includes optimization of cutting parameters, cooling and lubrication technology, cutting force and heat control, etc., to achieve efficient, precise and stable processing.

3. Build an intelligent high-speed cutting cloud processing database

 

The high-speed cutting processing database can intelligently provide process data for the cutting site according to production needs. The core of the high-speed cutting database is based on the intelligent prediction of cutting force model, cutting temperature model, tool wear model and workpiece surface quality model.

However, with the continuous development of new processes and technologies, the cutting database has a strong timeliness.

At present, cloud computing technology and artificial intelligence theory can be used to build an intelligent high-speed cutting cloud processing database based on the physical model of the high-speed cutting process, combined with production practice and a large number of cutting tests.

4. Research on online monitoring technology for high-speed cutting process

 

During high-speed cutting, the vibration and wear of the tool are crucial to the surface quality of the workpiece. To ensure the development of high-speed cutting technology, online monitoring of the tool status and workpiece surface quality has become crucial.

Online monitoring establishes a connection between the vibration and wear of the tool and the surface quality of the workpiece, and sets a reasonable threshold based on a large amount of actual production experience.

This monitoring can ensure that the tool vibration signal is normal and the surface roughness of the workpiece is qualified. By adjusting the process parameters, replacing the tool, and adjusting the equipment through feedback, the normal high-speed cutting can be guaranteed.

5. Research on green cutting technology based on dry cutting

 

High-speed cutting can indeed reduce energy consumption to a certain extent, but it also requires a large amount of coolant, which causes certain pollution to the environment. The main development direction of the manufacturing industry in the future is green environmental protection and energy conservation and emission reduction.

Among them, green cutting based on dry cutting is one of the key research areas of high-speed cutting. Dry cutting is a processing technology that does not use or only uses a trace amount of cutting fluid during the processing.

This technology can not only reduce pollution, but also save equipment related to cutting fluid, simplify the production system, and reduce production costs, which is in line with the trend of green environmental protection and energy conservation and emission reduction.

Conclusion

 

The following conclusions can be drawn from the above research:

1. High-speed cutting technology is the key research content in the current advanced manufacturing field, covering complex system engineering such as high-speed cutting mechanism, key equipment technology and process. With the development of related technologies, we continue to pursue the organic unity of technology and benefits.

2. Compared with conventional cutting, high-speed cutting technology has many advantages: high removal rate reduces production costs, small cutting force reduces machining deformation, chip heat dissipation reduces thermal deformation, stable cutting and high precision, simplified process flow improves production efficiency.

3. To promote the development of high-speed cutting technology, we need to strengthen the research on high-speed cutting mechanism, accelerate the development of ultra-high-speed and high-power machine tools, strengthen the research on new tool materials and structural technologies, build an intelligent high-speed cutting cloud processing database, carry out research on online monitoring technology of high-speed cutting process, and focus on strengthening green cutting technology mainly based on dry cutting.