1. Technical Advantages of High-Speed Machining
The theory of high-speed cutting was proposed by German physicist Carl J. Salomon in the early 1930s. He concluded through a large number of experimental studies within the normal cutting speed range. If the cutting speed is increased, the cutting temperature will rise, which will aggravate the wear of the cutting tool.
However, once the cutting speed surpasses a certain inflection point, as the cutting speed increases, the cutting temperature will not rise, but will drop. Therefore, a high enough cutting speed could mitigate the issues of excessive cutting temperature and tool wear, which are unfavorable for cutting, and would result in good processing efficiency.
With the development of the manufacturing industry, this theory has gradually been valued, and attracted a lot of research attention. On the basis of this theory, the research field of CNC high-speed cutting technology has gradually formed. The research of CNC high-speed cutting technology in developed countries is relatively early.
After going through theoretical basic research, applied basic research, and applied research and development and application, this technology has entered a substantive application phase in certain fields.
In terms of classifying high-speed cutting, there are generally several methods:
- One approach defines it based on the cutting speed, considering any speed that is 5-10 times higher than the conventional cutting speed to be high-speed cutting.
- Some scholars define high-speed machining based on the spindle speed, classifying any speed higher than 8000r/min as high-speed.
- Another definition, which considers machine tool spindle design, is determined by the product DN of the spindle diameter and the spindle speed. If the DN value reaches (5 ~ 2000) × 10^5mm.r/min, it is considered high-speed machining.
Different processing methods and materials yield different high-speed cutting speeds. It is generally believed that turning speeds of (700-7000) m/min and milling speeds of (300-6000) m/min qualify as high-speed cutting. Additionally, in practical production, high-speed cutting not only involves the speed of the cutting process but also includes the integration and optimization of the process.
It represents a high-speed cutting process that provides good economic benefits and unifies technology and benefits. High-speed cutting technology is based on machine tool structure and materials, machine tool design, manufacturing technology, high-speed spindle systems, fast feed systems, high-performance CNC systems, high-performance toolholder systems.
High-performance tool material and tool design and manufacturing technology, high-efficiency and high-precision measurement testing technology, high-speed cutting mechanisms, and various related hardware and software technologies. Therefore, high-speed cutting technology is a complex system of engineering that continues to develop with the evolution of related technologies.
Due to the substantial increase in cutting speed, high-speed cutting processing technology not only improves the productivity of cutting processes but also presents several advantages over conventional cutting:
Cutting Force is Reduced
In high-speed milling processing, the use of smaller cutting amounts and a high cutting speed form reduce the cutting force by more than 30% compared to conventional cutting. In particular, the radial cutting force exerted on the spindle bearing, tool, and workpiece is greatly reduced. This not only minimizes tool wear but also effectively controls the vibration of the processing system, contributing to enhanced processing accuracy.
Material Removal Rate is High
With high-speed cutting, the cutting speed and feed rate are significantly increased, and the material removal rate within the same time frame is also markedly increased. This significantly boosts processing efficiency.
Thermal Deformation of the Workpiece is Minimal
During high-speed cutting, most of the cutting heat is expelled by the high-speed outflow of chips before it can transfer to the workpiece. Therefore, the processing surface experiences a short heating period, avoiding thermal deformation due to temperature rise.
This benefits the surface precision and the physical and mechanical properties of the processed surface, making them superior to those achieved by ordinary processing methods.
High Machining Accuracy
High-speed cutting typically involves a relatively small feed rate, which reduces the roughness of the machined surface. Because the cutting force is less than that of conventional cutting, the vibration of the machining system is diminished and the machining process becomes more stable, yielding good results. This indicates enhanced quality and facilitates high precision and low roughness processing.
Environmental Friendliness
During high-speed cutting, the processing time of the workpiece is reduced, and the utilization rate of energy and equipment is improved. This results in high processing efficiency and low energy consumption. Additionally, due to high-speed cutting, dry cutting can be realized, reducing or even eliminating the use of cutting fluid, thereby reducing pollution and energy consumption.
2. Development Status of CNC High-Speed Machining
Practical high-speed machining technology has been widely adopted in the machinery manufacturing industry, following the introduction of advanced CNC automatic production lines, cutting tools, and CNC machine tools. The corresponding management models, technologies, and concepts have been integrated into enterprises.
This technology has been applied to varying degrees in industries such as aerospace, aviation, steam turbines, and molds. The gap between these industries lies in the amount of state investment, the introduction of policy support, and the depth of entrepreneurs’ understanding of high-speed processing system technology.
Compared with the automobile manufacturing industry, this type of machinery manufacturing industry essentially belongs to process-discrete manufacturing. Its high-speed machining technology is mainly characterized by the application of high-speed CNC machine tools and cutting tool technology.
Today, for processing cast aluminum, wrought aluminum alloy bodies, high-strength cast iron, and structural steel parts, ultra-fine carbide and coated carbide tool materials are predominantly used. Tools with standard structures are also common. However, the application of superhard tool materials and special structural tools is still relatively rare. The spindle speed of machine tools is quite low, generally cannot enter the field of high-speed cutting.
For instance, taking milling into consideration, these industries process aluminum alloy workpieces with a cutting speed of less than 1000 m/min, a feed speed of less than 15 m/min, and a feed rate per tooth of less than 0.35 mm. The cutting speed in turning is less than 700 m/min.
When milling cast iron and structural steel workpieces (including stainless steel), the cutting speed is less than 500 m/min, the feed speed is less than 10 m/min, and the feed rate per tooth is less than 0.3 mm. It is worth noting that in the aforementioned industries, the utilization rate of CNC equipment is only around 25%.
3. Key Technologies of CNC High-Speed Machining Tools
High-speed machine tools are the premise and key to realizing high-speed cutting. The high-precision, high-speed spindle, along with the axial feed system, which boasts high control precision and impressive axial feed speed and feed acceleration, are the crucial elements of high-speed machine tools. The breakdown is as follows:
High-Speed Spindle
The high-speed spindle is one of the most critical parts of high-speed cutting. Currently, machining centers with spindle speeds ranging from 10,000 to 20,000 rpm are becoming increasingly popular. Practical high-speed spindles with speeds of 100,000 rpm, 200,000 rpm, and 250,000 rpm are also under development.
The high-speed spindle rotates at an extremely high speed, causing the spindle parts to vibrate and deform due to the effects of centrifugal force. The friction created by high-speed operation and the heat generated by the high-power built-in motor can lead to high temperatures and deformation, necessitating strict control. Therefore, the following performance requirements are put forward for the high-speed spindle:
- High speed and high speed range
- Sufficient rigidity and high rotational accuracy
- Good thermal stability
- High power
- An advanced lubrication and cooling system
- A reliable spindle monitoring system
Rapid Feed System
In high-speed cutting, maintaining a consistent feed rate per tooth of the tool requires increasing the feed rate in proportion to spindle speed. Currently, the feed speed of high-speed cutting can reach an impressive 50m/min to 120m/min. Achieving and accurately controlling such feed speed requires new expectations for machine tool guide rails, ball screws, servo systems, and worktable structures.
Because the stroke of linear motion on the machine tool is generally short, it’s practical for high-speed machining machine tools to accomplish higher feed acceleration and deceleration. To meet the requirements of high-speed feed movement, high-speed processing machine tools commonly adopt the following measures:
- Utilizing a new type of linear rolling guide rail. The contact area between the ball bearing and the steel guide rail in the linear rolling guide rail is minute, and the friction coefficient is about 1/20 of the trough guideway. Using a linear rolling guideway significantly reduces the “crawling” phenomenon.
- Implementing a high-speed feed mechanism with a small-pitch large-size high-quality ball screw or a coarse-pitch multi-head ball screw. The aim is to gain higher feed speed and feed acceleration/deceleration without sacrificing accuracy.
- Developing the high-speed feed servo system into a digital, intelligent, and software-based system. High-speed cutting machines have begun to adopt full-digital AC servo motor and control technology.
- Using carbon fiber reinforced composite materials in the high-speed feed mechanism to reduce table weight as much as possible without compromising rigidity.
- Increasing feed speed, advanced higher speed linear motors are being developed. The linear motor eliminates issues like backlash and elastic deformation of the mechanical transmission system, reducing transmission friction and having almost no backlash. The linear motor provides high acceleration and deceleration characteristics, with acceleration reaching 2g, which is 10 to 20 times that of traditional drive devices.
The feed speed is 4 to 5 times that of traditional drives. Being driven by a linear motor, it offers substantial thrust per unit area and is readily capable of producing high-speed motion. It also presents the clear advantage of a mechanical structure requiring no maintenance.
High-Speed Cutting Tool Technology
Tool Material
High-speed cutting requires that the tool material possess a low chemical affinity for the material being processed. The tool material should have excellent mechanical properties, thermal stability, impact resistance, and wear resistance. Today, the materials commonly used for high-speed cutting tools include single-coated or multi-coated cemented carbide, ceramics, cubic boron nitride (CBN), and polycrystalline diamond, among others.
High-Speed Cutting Tool Structure
The centrifugal force generated by high speeds can fracture blades with low bending strength and fracture toughness during high-speed cutting. This can not only damage the workpiece but also pose a risk to the operator and the machine tool. Therefore, high-speed cutting tools must meet dynamic balance requirements in addition to static balance.
Dynamic balance is generally not a strict requirement for small-diameter tools but is critical for large-diameter or disc tools. A tool with a long overhang must be dynamically balanced. Moreover, each component, such as the tool, chuck, and spindle, needs to be individually balanced, and the combination of the tool and the chuck must also be balanced.
Finally, the tool should be balanced alongside the spindle. However, there is currently no uniform balance standard. There are different opinions on the balance quality G value standard in the ISO1940-1. Some companies use G1 as the standard (G1 signifies that when the tool rotates at 10,000 r/min, the deviation between the rotating shaft and the central axis of the tool is only allowed to be 1µm), while others use G2.5 as their standard.
High-Speed Cutting Tool Geometry Parameters
The shape of the high-speed cutting tool blade is evolving towards higher rigidity, a composite structure, multi-blade designs, and superior surface finishing. The geometric parameters of the tool greatly influence the machining quality and tool durability. Generally, the rake angle of the high-speed cutting tool is on average 10° smaller than that of traditional machining tools, while the clearance angle is about 5°-8° larger.
To prevent thermal wear at the tool tip, rounding or chamfering should be applied at the junction of the main and minor cutting edges. This increases the tool tip angle, extends the cutting edge near the tool tip, enhances the tool’s rigidity, and reduces the likelihood of blade breakage.
The table presents various geometry parameters of high-speed cutting tools, including rake angle, clearance angle, and the use of tool tip rounding or chamfering to improve tool rigidity and machining performance while preventing blade breakage and thermal wear.
| Geometry Parameter |
Average Value |
Purpose/Effect |
| Rake Angle |
10° smaller |
Influences machining quality |
| Clearance Angle |
5°-8° larger |
Affects tool durability |
| Tool Tip Rounding/Chamfering |
Applied at the junction of the main and minor cutting edges |
Prevents thermal wear and enhances tool rigidity |
| Tool Tip Angle |
Increased |
Reduces likelihood of blade breakage |
| Cutting Edge Extension |
Near the tool tip |
Enhances the cutting edge near the tool tip |
High-Speed Cutting Tool Holder System
Most connections between the machining center spindle and the tool adopt a single-sided clamping tool holder system with a 7:24 taper. Systems such as ISO, CAT, DIN, BT, and others, all fall within this category. When used in high-speed cutting, this type of system presents several issues, including insufficient rigidity, unstable repeatability of ATC (automatic tool change), significant influence from centrifugal force, and a large taper of the tool holder, which is not conducive to rapid tool changing and miniaturization of machine tools.
To address these issues and improve the connection rigidity and clamping accuracy between the tool and the machine tool spindle, tool holders with double-sided positioning have been developed. These closely contact the cone surface and end surface of the spindle’s inner hole.
There are two main categories of double-sided positioning tool holders: one is the improved design of the existing 7:24 taper tool holders, such as BIG-PLUS, WSU, ABSC, and other systems. The other category includes innovative designs like the 1:10 hollow short taper, with several types of tool handling systems, such as HSK developed in Germany and KM developed in the United States.
High-Speed Cutting Process
High-speed cutting boasts advantages such as high processing efficiency, high processing precision, and low single-piece processing cost. However, high-speed processing differs from traditional processing technology. Traditional processing posits that high efficiency derives from low speed, large cut depth, slow feed, and a single stroke.
Conversely, in high-speed processing, high speed, medium depth of cut, fast feed, and multiple strokes are preferred. As a novel cutting method, high-speed cutting lacks a comprehensive set of processing parameters for selection, and there are not many processing examples to use as a reference. A practical high-speed cutting database has yet to be established. Consequently, there is a lot of optimization work that still needs to be done.
NC programming for high-speed cutting calls for alterations to standard operating procedures. The part program needs to be precise, and it must ensure stability in the cutting load. The automatic programming in most CNC software fails to meet the requirements of high-speed cutting, necessitating supplementation with manual programming.
A new programming method should be implemented to ensure the cutting data aligns with the power characteristic curve of the high-speed spindle. Currently, CAM software such as Cimatron, Mastercam, UG, and Pro/E have all added programming modules tailored for high-speed cutting.
Bed, Column, and Table of High-Speed Machine Tools
Through computer-aided engineering methods, particularly optimal design using finite elements, a bed and workbench featuring reduced weight and increased rigidity can be achieved.
Dive Deeper Into Our Resources
Looking for more diverse service options? Browse through our handpicked selections:
For some insightful reads, we’ve curated a list of recommended articles just for you:
Still haven’t found what you’re looking for? Don’t hesitate to contact us. We’re available around the clock to assist you.
4. Conclusion
High-speed machining technology is a cutting-edge advancement in modern manufacturing. Its development is the cumulative result of a global market economy and the progression of various state-of-the-art technologies. Emerging in response to these trends, high-speed machining technology has evolved into a comprehensive system of engineering technology that is being increasingly utilized.
One of its most compelling features is its ability to ensure accuracy while operating at high speeds. The recognition and growing demand for high-speed machining in industries such as aerospace, automotive, and mold manufacturing has spurred the global advancement of this technology.
