A comprehensive analysis of CNC cutting tools

I. Basic Concepts of CNC Cutting Tools

CNC cutting tools are tools used for cutting processes in mechanical manufacturing, also known as cutting tools. In a broad sense, cutting tools encompass not only cutting tools but also grinding wheels; while "CNC cutting tools" include not only the inserts used for cutting but also accessories such as tool holders and tool shanks. They play a crucial role in the field of mechanical manufacturing and are a key element in achieving precise cutting processes.

The advent of CNC cutting tools has greatly improved the efficiency and precision of machining. In traditional machining, manual operation of cutting tools is not only inefficient but also makes it difficult to guarantee accuracy. CNC cutting tools, with the precise control of CNC machine tools, can perform automated cutting according to pre-set programs, significantly improving production efficiency and product quality. For example, in the manufacturing of automotive parts, CNC cutting tools can precisely machine parts of various shapes and sizes, ensuring the performance and safety of automobiles.

II. Classification of CNC Cutting Tools

Classification by structure

CNC cutting tools can be classified into integral, welded, mechanically indexed, and special types according to their structure. Integral tools are molded from a single blank and are not detachable. These tools have a simple structure and good rigidity, but if any part of the tool is damaged, the entire tool needs to be replaced. Welded tools connect the tool head and tool holder using a welding method. They allow for the selection of appropriate tool head and tool holder materials according to different machining requirements, thus improving the cutting performance. However, stress concentration may occur during the welding process, affecting the tool's lifespan. Mechanically indexed tools can be further divided into non-indexable and indexable types; mechanically indexable tools are more commonly used in CNC machining. Indexable tools allow the inserts to be indexed or replaced after wear, improving insert utilization and reducing tool costs. Special types of cutting tools, such as composite tools and vibration-damping tools, have special functions and are suitable for specific machining applications.

Classified by material

CNC cutting tools can be classified by material, including high-speed steel tools, cemented carbide tools, diamond tools, and tools made from other materials such as cubic boron nitride tools and ceramic tools. High-speed steel tools possess high strength and toughness, offering good cutting performance and are suitable for applications where cutting speed requirements are not high. Cemented carbide tools are among the most widely used tool materials in CNC machining. They possess high hardness, high wear resistance, and good thermal stability, enabling them to withstand high cutting speeds and forces, and are suitable for machining various metal materials. Diamond tools have extremely high hardness and wear resistance, primarily used for machining non-ferrous metals, non-metallic materials, and some high-hardness alloys. Cubic boron nitride tools and ceramic tools possess high hardness and thermal stability, making them suitable for high-speed cutting and hard cutting processes.

Classification by cutting process

According to cutting processes, CNC cutting tools can be classified into turning tools, drilling tools, boring tools, and milling tools. Turning tools include various types such as external turning, internal turning, threading, parting, and grooving tools, used for machining the external diameters, internal holes, and threads of rotating parts. Drilling tools include drills, reamers, and taps, used for drilling, enlarging, and tapping holes in workpieces. Boring tools are used for boring the internal holes of workpieces, improving the dimensional accuracy and surface quality of the internal holes. Milling tools are used to machine surfaces of various shapes, such as planes, steps, and grooves.

III. Characteristics of CNC Cutting Tools

Reasonableness of economic life indicators and durability of knives or blades

In the production of CNC machining tools, tool durability is a crucial indicator of tool quality. Because cutting tool production is affected by objective factors such as grinding quality, cutting tools produced under the same environment can exhibit varying durability. For CNC tools, both the average tool durability index and the reliability index Tp should be complete, and the standard tool reliability should generally not be lower than 0.9. This is because CNC machining is often mass production; if tool durability is unstable, frequent tool replacements will affect production efficiency and product quality. For example, in the machining of automotive engine blocks, using tools with unstable durability may lead to inconsistent machining accuracy, thus affecting engine performance.

Blades or cutting tools facilitate cutting control

CNC machine tools are typically equipped with multiple cutting tools and handle large cutting volumes. When machining ductile metals, it is crucial to ensure that the cutting tools are not entangled in chips, and to control the indiscriminate spraying of cutting material to guarantee the safety of the operator, ensure the accuracy of part feeding and positioning, and avoid affecting the quality of coolant spraying. To improve chip breaking performance, methods such as vibratory cutting and chip-breaking tools can be employed. For example, when machining aluminum alloy parts, using tools with excellent chip-breaking properties can effectively prevent chips from entangled in the tool, improving machining efficiency and surface quality.

Typicality and standardization of cutting parameters and geometric parameters of inserts or tools

The precision of CNC cutting tools needs to be effectively guaranteed, mainly including the accuracy of the tool shape, the relative positional accuracy of the tool holder and insert to the CNC machine tool spindle, and the repeatability of tool holder and insert assembly, disassembly, and indexing. The variation range of the geometric dimensions of the cutting part of the CNC cutting tool should be controlled within a certain range and should not be too large. Furthermore, it is also necessary to control the stability of the accuracy of repeated assembly and disassembly of the tool body, inserts, and tool holder. This is because precise cutting and geometric parameters are crucial to ensuring machining accuracy and surface quality. For example, in the machining of precision molds, using low-precision tools will lead to increased dimensional deviations and surface roughness of the mold, thereby affecting the mold's service life and product quality.

Optimize the automatic tool changer and positioning reference system for tool holders and inserts.

The changing of CNC tools requires automation and speed, which necessitates a high degree of standardization, universality, and serialization of tool holders and inserts. Tools should have functions for adjusting and controlling dimensions or devices for automatically compensating for tool wear to accelerate tool change and adjustment speeds. In modern CNC machine tools, automatic tool changing systems can complete tool changes in a very short time, greatly improving production efficiency. For example, in machining centers, by optimizing the automatic tool changing and positioning reference systems for tool holders and inserts, fast and accurate tool changes can be achieved, improving machine tool utilization.

IV. Selection of CNC Cutting Tools

CNC tool model

The unified standard for cutting tool manufacturers both domestically and internationally is ISO, with different numbers representing different tool parameters. When selecting CNC cutting tools, the specific machining requirements and workpiece material should be considered, along with their specific geometric parameters. For example, when machining stainless steel, a tool model suitable for stainless steel machining needs to be selected to ensure the tool's cutting performance and service life.

Blade shape selection

The shape of CNC turning inserts is primarily determined by the shape of the workpiece and is a crucial factor in tool selection. Insert shape includes the tip angle, principal cutting edge angle, and number of effective cutting edges. Generally, tip strength increases with the tip angle; tools with smaller tip angles are suitable for machining complex surfaces, such as grooves or downslope excavation. The type of insert is also important; types with cutting edges on both sides (A, G, N, etc.) are more likely to be selected because they improve insert utilization. The tip radius is closely related to the cutting efficiency of the CNC tool, the accuracy of the workpiece, and its surface roughness. When selecting a tool, ensure that the tip radius is ≥ 1.25 times the maximum feed rate. For turning with small allowances, a small feed rate requires a sufficiently small tip radius; a large feed rate requires a sufficiently large tip radius. For example, during finishing, the radius of the tool tip arc is usually set to 0.2, 0.4, or 0.8; during semi-finishing, it is set to 0.4, 0.8, or 1.2; and during roughing, it is set to 0.8, 1.2, 1.6, or 2.4.

Tool type selection

When selecting cutting tools, the tool strength must meet certain standards and must not conflict with the workpiece. The tool shank head shape should primarily be determined by straight head and principal cutting edge angle. During use, the relationship between the insert type and the workpiece shape must be carefully considered. When selecting the type of turning tool, the principal cutting edge angle should be the primary consideration. If the workpiece has right-angle steps, the principal cutting edge angle should be ≥90°; for roughing, the principal cutting edge angle should be 45°～90°; for finishing, the principal cutting edge angle should be 45°～75°. When the machining system has sufficient rigidity, the principal cutting edge angle should be sufficiently small; when the machining system has weak rigidity, the principal cutting edge angle should be sufficiently large. Furthermore, a suitable insert clamping method needs to be selected. Currently, insert clamping methods are mainly divided into C, D, M, P, and S. The specific selection should be determined based on the insert shape and cutting strength.

Tool holder size selection

The basic dimensions of a tool shank include its length and width, and the tip height. Within standard system dimensions, there is a one-to-one correspondence between the length, width, and height of the tool shank. The tool shank dimensions should match the machine tool, and the tip height needs to be matched with the machine tool with the assistance of the tool holder and tool pad. The tool shank length is determined based on the clamping overhang and length; the overhang of an external turning tool shank is typically 1.5 times the tip height. The overhang of an internal turning tool is a reference for determining the position of the tool being machined and the hole depth. For example, when machining deep holes, it is necessary to select an internal turning tool shank of appropriate length to ensure tool rigidity and machining accuracy.

V. Modernization of CNC Cutting Tools

Modern high-efficiency cutting tools, commonly referred to as CNC cutting tools in China, are an important component of modern digital manufacturing technology. Looking at international developments, high-efficiency cemented carbide cutting tools are the mainstream products. In recent years, the development of superhard cutting tools, such as synthetic diamond tools and cubic boron nitride tools, has also been rapid, with their usage share increasing rapidly from 2%-3% in the past. In developed countries, cemented carbide cutting tools account for more than 70% of all cutting tool sales.

my country's development in the field of CNC cutting tools has gone through a process from slow to rapid. At the end of the last century, although my country's annual output of metal cutting machine tools reached 190,000 units, only 14,000 of them were CNC machine tools, a relatively small proportion. Meanwhile, modern high-efficiency cutting tools, represented by new high-efficiency carbide cutting tools, accounted for less than 15% of the total sales of cutting tools in my country. Since the beginning of the new century, with the accelerated modernization of my country's manufacturing industry, my country's digital manufacturing technology has developed rapidly. By 2007, my country's output of CNC machine tools reached 123,200 units, with a CNC rate of 43.7% in output value. Correspondingly, the proportion of high-efficiency carbide cutting tools also rose to 40.3% of the total cutting tool sales. Currently, domestically produced modern high-efficiency cutting tools have entered various fields such as the automotive industry, mold industry, aerospace, power generation equipment, and general machinery in batches. The performance of some products has reached or approached the international advanced level, effectively breaking the monopoly of some imported cutting tools in certain fields and contributing to the standardized competition in my country's high-efficiency cutting tool market.

However, a significant gap still exists between my country and developed countries. In developed countries, the CNC rate of machine tools is over 70%, and modern high-efficiency cutting tools (carbide high-efficiency cutting tools) also account for over 70%, while in my country, this figure is only around 40%. Many of my country's CNC machine tools are still rudimentary CNC machines, and a considerable number of carbide cutting tools are still ordinary carbide tools. Therefore, my country's tool enterprises must recognize development trends and resolutely accelerate the modernization of their cutting tools.

VI. The Development History and Future Prospects of CNC Cutting Tools

The development of knives has played a vital role in the history of human progress. In China, as early as the 28th to 20th centuries BC, bronze awls, drills, and knives made of brass and copper already existed. During the late Warring States period, thanks to the mastery of carburizing technology, bronze knives were manufactured, and the drills and saws of that time already bore some resemblance to modern flat drills and saws.

The rapid development of cutting tools began in the late 18th century, accompanying the development of machines such as the steam engine. In 1783, René of France first invented a milling cutter; in 1792, Maudsley of England invented taps and dies; the earliest documented invention of the twist drill dates back to 1822, but it wasn't commercially produced until 1864. At that time, cutting tools were made of solid high-carbon tool steel, with a permissible cutting speed of approximately 5 meters per minute. In 1868, Mushet of England developed tungsten-containing alloy tool steel; in 1898, Taylor and White of the United States invented high-speed steel; and in 1923, Schröter of Germany invented cemented carbide. With the continuous development of cutting tool materials, the cutting speed and machining quality of cutting tools have also continuously improved. When using alloy tool steel, the cutting speed increased to approximately 8 meters per minute; with high-speed steel, it more than doubled; and with cemented carbide, it more than doubled compared to high-speed steel, and the surface quality and dimensional accuracy of the machined workpieces were also greatly improved.

Due to the high cost of high-speed steel and cemented carbide, cutting tools developed welded and mechanically clamped structures. Between 1949 and 1950, the United States began using indexable inserts on lathe tools, which were soon applied to end mills and other cutting tools. In 1938, the German company Degussa obtained a patent for ceramic cutting tools; in 1972, General Electric in the United States produced polycrystalline synthetic diamond and polycrystalline cubic boron nitride inserts, non-metallic tool materials that enabled cutting at higher speeds. In 1969, Sandvik Steel in Sweden obtained a patent for producing titanium carbide-coated cemented carbide inserts using chemical vapor deposition; in 1972, Bunza and Lagoland in the United States developed physical vapor deposition to coat the surface of cemented carbide or high-speed steel cutting tools with a titanium carbide or titanium nitride hard layer. This surface coating method combines the high strength and toughness of the base material with the high hardness and wear resistance of the surface layer, giving the tool better cutting performance.

Looking to the future, CNC cutting tools will evolve towards higher precision, higher efficiency, and greater environmental friendliness. With the continuous upgrading of the manufacturing industry, the performance requirements for CNC cutting tools are becoming increasingly stringent. For example, in high-end manufacturing sectors such as aerospace and electronics, there is a need to machine parts with higher precision and more complex shapes, which demands higher precision and better cutting performance from CNC cutting tools. Simultaneously, to meet the requirements of energy conservation and emission reduction, the manufacturing and use of CNC cutting tools will place greater emphasis on environmental protection. This includes using recyclable tool materials and reducing the use of cutting fluid. Furthermore, intelligentization is also a significant trend in the development of CNC cutting tools. Future CNC cutting tools will be more closely integrated with CNC machine tools, possessing functions such as automatic monitoring and automatic compensation, improving the intelligence and reliability of the machining process.