CNC lathes are becoming increasingly crucial in the manufacturing sector. To ensure the quality of turned parts, lathe tools must be adapted to meet the demands of high efficiency, high speed and high automation.
See too:
- The 10 largest lathe manufacturers in the world
This article will provide an overview of CNC lathe tools, discussing the different types of tools and how to select the appropriate ones.
The widespread use of CNC lathes in production has made the formation of a quantitative production line and the development of CNC programming a crucial aspect of CNC processing.
During the NC programming process it is necessary to choose tools and determine cutting parameters in real time through human-computer interaction.
Therefore, programmers must have knowledge about the methods of selecting cutting tools and the principles of determining cutting parameters to ensure the quality and efficiency of the parts being processed. This, in turn, maximizes the benefits of using CNC lathes and increases the company's economic efficiency and production level.
I . Structure of CNC Tools
The variety of CNC lathe tools is vast, each with different functions. Selecting the right tool based on different processing conditions is an essential step in compiling the program, therefore, a basic knowledge of the types and characteristics of lathe tools is necessary.
The tools used in CNC lathes include circular lathe external tools, drill bits, boring tools, cutting tools, thread processing tools, etc., among which circular lathe external tools, boring tools and drill bits are the most commonly used.
Lathe tools, boring tools, cutting tools and thread processing tools used in CNC lathes are divided into integral types and machine-attached types. In addition to economical CNC lathes, the type of indexable lathe tool attached to the machine is now widely used.
(1) Features of indexable tools for CNC lathes
The geometric parameters of indexable lathe tools used in CNC lathes are formed by combining the shape of the blade structure and the orientation of the blade groove in the tool body.
Compared with general lathes, there is generally no essential difference, and its basic structure and functional characteristics are the same.
However, the processing procedures of CNC lathes are completed automatically, so the requirements for indexable lathe tools are different from those used in general lathes. Specific requirements and characteristics are shown in the following table.
Table 2-2 Characteristics of Indexable Lathe Tools
| Requirements | Characteristics | goal |
| High precision | Use cutting blades with precision level M or higher;
Employ precision tool holders more frequently; Pre-configured tool holders with micro-adjustment devices outside the machine. |
Ensure the repeatability of blade positioning, facilitate coordinate adjustment, and ensure the accuracy of tool tip position. |
| High reliability | Use turning tools with highly reliable chip-breaking groove types or those with chip-breaking platforms and chipbreakers;
Employ structurally sound turning tools using composite fixture frames and other reliably clamped structures. |
The chip breaking must be stable, without disorders or ribbon-shaped chips; it must accommodate rapid movement and repositioning of the tool holder and there must be no loosening throughout the automatic cutting process. |
| Quick tool change | Adopting a turning tool system;
Using a quick change tool holder. |
Quickly change various shapes of cutting components to complete a wide range of cutting processes, thereby increasing production efficiency. |
| Blade material | Coated blades are commonly used. | Meet production rate requirements and improve processing efficiency. |
| Rod cross section | Many tool holders use square tool shanks, but due to significant differences in tool holder system structures, some require the use of specialized tool shanks. | The tool shank corresponds to the tool holder system. |
(2) Types of indexable turning tools
Indexable turning tools can be categorized according to their uses into outer circle turning tools, profile turning tools, end face turning tools, inner circle turning tools, grooving turning tools, tools cutting turning tools and thread turning tools as shown in Table 2-3.
Table 2-3 Types of Indexable Turning Tools
| Type | Main cutting angle | Applicable machine tools: |
| External Turning Tool | 900,500,600,750,450 | Conventional Lathe and CNC Lathe, |
| Profile Turning Tool | 930、107.50 | Profile lathe and CNC lathe, |
| End Face Turning Tool | 900、450、750 | Conventional Lathe and CNC Lathe, |
| Internal Turning Tool | 450,600,750,900,910,930,950,107,50 | Conventional Lathe and CNC Lathe, |
| Partition Tool | Conventional Lathe and CNC Lathe, | |
| Line Cutting Tool | Conventional Lathe and CNC Lathe, | |
| Channel Tool | Conventional Lathe and CNC Lathe. |
(3) Structural forms of indexable turning tools:
① Lever type:
As shown in Figure 2-16, it is composed of a lever, screw, shim, shim pin, and cutting insert. This method depends on the force exerted by the lever that presses the screw to secure the cutting insert.
It adapts to all types of positive and negative tilt angles, with an effective tilt angle range of -60° to +180°. Chips can flow without obstruction, and cutting heat does not affect the screw hole and lever. The two groove walls provide strong support for the cutting insert and ensure indexing accuracy.
② Wedge type:
As shown in Figure 2-17, it consists of a set screw, shim, pin, wedge and cutting insert. This method relies on the compression force between the pin and wedge to secure the cutting insert.
It adapts to all types of negative tilt angles, with an effective tilt angle range of -60° to +180°. There are no slot walls on both sides, which is suitable for profile cutting or reverse operation with clearance.
③ Wedge fastening type:
As shown in Figure 2-18, it consists of set screw, shim, pin, pressure wedge and cutting insert. This method relies on the downward force of the pin and wedge to secure the cutting insert.
It has the same characteristics as the wedge type, but the chip flow is not as smooth as the wedge type.
In addition, there are other types such as screw pressing, hole pressing and top pressing.
II. Blade material
The quality of cutting performance of tool materials directly affects the productivity of cutting operations and the quality of the machined surface.
The emergence of new tool materials often significantly improves productivity, becoming the key to processing certain difficult-to-machine materials and stimulating the development and upgrade of machine tools.
(1) Requirements for the material of tool cutting parts
During metal cutting, the cutting part of the tool is subjected to high pressure, high temperature and intense friction; When the machining tolerance is irregular or the cutting surface is discontinuous, the tool is also subject to impact.
To ensure that the tool can perform cutting work, the material for the cutting parts of the tool must have the following cutting performance:
① High hardness and wear resistance
The tool must be harder than the workpiece to cut chips from it. At room temperature, the hardness of the tool should be above 60HRC. The higher the hardness of the tool material, the better its wear resistance.
② Sufficient strength and endurance
To withstand pressure and impact during the cutting process, the tool material must have sufficient strength and toughness.
③ High heat resistance and chemical stability
Heat resistance refers to the ability of the tool material to maintain its cutting performance under high temperature conditions. Heat resistance is expressed in terms of heat resistance temperature.
The heat resistance temperature refers to the maximum temperature that can basically maintain the cutting performance of the tool. The better the heat resistance, the higher the allowable cutting temperature for the tool material.
Chemical stability refers to the ability of the tool material to resist chemical reactions with the workpiece material and the surrounding medium under high temperature conditions, including antioxidant and anti-adhesion ability.
The greater the chemical stability, the slower the tool wear. Heat resistance and chemical stability are the main indicators for measuring tool cutting performance.
In addition to excellent cutting performance, tool materials must also have good processability and economy.
These include: tool steel must have minimum hardening deformation, shallow decarburization layer and good hardenability; high hardness materials must have good grinding performance; hot-rolled forming tools must have good plasticity at high temperatures; the welding performance of materials used in welding tools must be good; the tool materials used should be as rich and cheap as possible in our country's resources.
(2) Commonly used cutting tool materials
Commonly used cutting tool materials can be categorized into four types: high speed steel (HSS), cemented carbides, ceramic materials and ultrahard materials.
① High Speed Steel
High-speed steel is a tool steel alloy that contains a significant amount of alloying elements such as tungsten, molybdenum, chromium and vanadium, with a carbon mass fraction of about 1%.
After heat treatment, the hardness of HSS reaches 62-65 HRC, with a heat resistance temperature of 550-600°C, flexural strength of about 3,500 MPa, and impact strength of approximately 0.3 MJ per square meter.
HSS has good strength and toughness, can withstand impacts and is easy to grind, making it the main material for manufacturing complex-shaped tools such as drills, milling cutters, broaching tools, thread cutters and gear cutters. Due to its limited heat resistance, HSS cannot be used for high-speed cutting.
② Cemented Carbides
Cemented carbides are formed by pressing and sintering a high hardness, high melting point powder of tungsten carbide (WC), titanium carbide (TiC), tantalum carbide (TaC), niobium carbide (NbC), using cobalt (Co) as a binder.
Its room temperature hardness is 88-93 HRA, with a heat resistance temperature of 800-1000°C, which is much harder, more wear-resistant and heat-resistant than HSS.
Therefore, the allowable cutting speed of carbide tools is 5 to 10 times higher than that of HSS tools. However, its flexural strength is only 1/2 to 1/4 of HSS, and impact strength is only a fraction of HSS. Cemented carbides are brittle and sensitive to impact and vibration.
Due to the significant increase in productivity provided by carbide tools, they are not only adopted for the vast majority of turning tools, planing tools, face mills, but also for a considerable number of drills, reamers and other cutters.
Nowadays, even complex broaching tools, thread mills and gear hobs are gradually being made from carbide.
In our country, there are currently three types of hard alloys commonly used:
Tungsten carbide alloys, composed of WC and Co, are coded as YG, similar to category K in ISO. They are mainly used to process brittle materials such as cast iron, non-ferrous metals and non-metallic materials.
Common brands include YG3, YG6 and YG8. The number indicates the percentage of Co, with the remainder being the percentage of WC.
In hard alloys, Co acts as a binder. The more Co the alloy contains, the better its toughness. Therefore, YG8 is suitable for rough machining and interrupted cutting, YG6 is suitable for semi-finished machining, and YG3 is suitable for fine machining and continuous cutting.
Tungsten-titanium-cobalt alloys are composed of WC, TiC and Co and are coded as YT, similar to category P in ISO. Because TiC is harder, more wear-resistant and heat-resistant than WC, but also more brittle, YT class alloys have higher hardness and heat resistance than YG class alloys. However, they are less resistant to impacts and vibrations.
As plastic deformation is significant in steel machining and the friction between the chip and the tool is severe, cutting temperatures are high. But because the chips are strip-shaped and the cutting is relatively stable, YT grade hard alloys are suitable for steel processing.
Common types of tungsten titanium carbide alloys include YT30, YTl5 and YT5. The number indicates the percentage of TiC. Therefore, YT30 is suitable for fine machining and continuous cutting of steel, YTl5 is suitable for semi-finished machining, and YT5 is suitable for rough machining and interrupted cutting.
Tungsten titanium tantalum (niobium) alloys are composed of a small amount of TaC or NbC added to class YT and are coded as YW, similar to category M in ISO. The hardness, wear resistance, heat resistance, bending resistance and impact resistance of YW grade hard alloys are all higher than those of YT grade, and the latter two indexes are similar to those of YG grade.
Therefore, YW class alloys can process steel and cast iron and non-ferrous metal chips and are known as universal hard alloys. Common brands include YWl and YW2, the former is used for semi-finished and fine machining, and the latter is used for rough and semi-finished machining.
At present, hard alloy cutting tools generally adopt coatings of high hardness materials such as TiC C, TiN and Al 2 Ó 3 . The service life of coated carbide tools is 2 to 10 times longer than their uncoated counterparts.
③ Ceramic Materials
Ceramic materials have greater hardness, wear resistance, heat resistance and chemical stability than carbides, but are more brittle. They are mainly used for precision machining.
The materials used for ceramic cutting tools include alumina ceramics, metal ceramics, silicon nitride ceramics (Si3N4) and Si3N4 composite ceramics. Since the 1980s, ceramic cutting tools have developed rapidly.
The bending strength and impact strength of metal ceramics, silicon nitride ceramics and composite ceramics are close to those of carbides, making them suitable for semi-finished machining and rough machining with cutting fluid.
④ Superhard Materials
Synthetic diamonds are created from graphite under high temperature and pressure through the catalytic action of metals. Synthetic diamonds are used to manufacture diamond grinding wheels and, after polycrystallization, to produce synthetic diamond wheels based on carbide substrates for cutting tools.
Diamonds are the hardest material in nature, with extremely high wear resistance and sharp cutting edges that can cut very fine chips. However, they are very brittle and have a strong affinity with ferrous metals, so they cannot be used for rough machining or ferrous chip cutting.
Currently, synthetic diamonds are mainly used as abrasives for grinding carbides. They can also be used for high-speed precision turning and boring of non-ferrous chips and their alloys.
Cubic boron nitride (CBN) is transformed from hexagonal crystalline boron nitride (also known as white graphite) under high temperature and high pressure. CBN has extremely high hardness and abrasion resistance, second only to diamond, and can withstand high temperatures of 1400 to 1500°C.
Does not react chemically with ferrous metals between 1200 and 1300°C.
However, it can chemically react with water at high temperatures, so it is generally used for dry cutting. CBN is suitable for precision machining of hardened steel, chilled cast iron, high temperature alloys, thermal spray materials, hard alloys and other difficult-to-process materials.
III. The shape of the blade
The “Select Blade Shape” icon is shown in Figure 2-20. The main parameter selection methods are as follows:
① Cutting edge angle
The size of the cutting edge angle determines the strength of the blade. Where the structure and rigidity of the part permit, as large a cutting angle as possible should be chosen. Typically, this angle is between 35° and 90°.
In Figure 2-19, the R-type circular blade has good stability during heavy cutting, but is prone to generating large radial forces.
② Blade shape selection
The shape of the blade is chosen mainly based on the surface shape of the part being processed, the cutting method, the tool life and the number of blade rotations, among other factors.
Equilateral triangular blades can be used for external circular turning tools, end face turning tools and internal hole turning tools with a main cutting edge angle of 60° or 90°. Due to the small cutting edge angle, low strength and low durability of this blade, it should only be used with smaller cutting quantities.
The square blades have a tip angle of 90°, which is greater than the 60° of equilateral triangular blades, and thus their strength and heat dissipation performance are improved. These blades are quite versatile and are mainly used for external circular turning tools, end face turning tools and boring tools with a main cutting edge angle of 45°, 60°, 75°, etc.
The pentagonal blades have a cutting angle of 108° and offer high resistance and durability, as well as a large heat dissipation area. However, they generate large radial forces during cutting and should only be used in situations where the machining system has good rigidity.
Circular and diamond-shaped blades are mainly used for shaping surfaces and processing arc surfaces. Its shape and size can be determined by referring to national standards in combination with the machining object.
4. Types of NC lathe tools
CNC lathes require increasingly stable, durable and easily replaceable tools.
In recent years, the use of interchangeable clamping tools for CNC machines has become widespread and they play a significant role in the machining process, making up a large part of the tools used.
What are the types of CNC lathe tools?
CNC lathe tools can be divided into three categories based on their structure: integral type, built-in type and special type.
Furthermore, they can be classified into four groups based on the material used to manufacture the tools: diamond tools, high-speed steel tools, carbide tools and tools made from other materials such as ceramics.
CNC lathe tools can also be classified based on the number of blades they have. They are either single-bladed tools or multi-bladed tools. Single-blade tools have only one main cutting edge, while multi-blade tools have two or more main cutting edges.
Compared with conventional lathe tools, CNC tools have different requirements, characterized by:
- High precision
- Good interchangeability
- Long service life
- Good rigidity (especially for rough machining tools)
- Convenient for quick tool changing
- Stable cutting performance
- Low resistance to vibration and thermal deformation
- Easy to adjust tool size to reduce tool change time
- Reliable chip or iron chip breaking capacity
Serialization and standardization are also necessary for efficient chip removal and to facilitate programming and tool management.
V. CNC lathe tool selection
The selection of tools in the CNC machining process is carried out through human-machine interaction.
See too:
- 10 CNC machining tips: for better machining quality
The programmer must make a proper selection of tools and tool holders for the CNC lathe by taking into consideration various factors such as processing capacity, processing procedures, material properties of the workpiece, cutting parameters and more.
The general rule for tool selection is to prioritize tools that are rigid, durable, accurate, and easy to install and adjust.
Although it still meets the processing requirements, it is recommended to choose tools with a shorter shank to increase rigidity during processing.
In the process of using an economical CNC lathe, grinding, measuring and tool replacement are performed manually, resulting in a long auxiliary time. It is crucial to organize the tool sequence efficiently to minimize this auxiliary time.
The general principles to follow are:
- Minimize the number of tools used
- Complete all machining steps with a single tool once clamped
- Use separate tools for roughing and finishing machining
- When machining with similar tools, prioritize surface finish machining first
- Choose a tool size that is compatible with the surface size of the part
- For free-form surface machining, ball head tools are often used for surface finishing
- Flat head milling cutters are preferred for roughing and finishing machining of curved surfaces as long as no cutting is guaranteed
It is important to note that the durability and precision of the tool are related to its cost. Although selecting a high-quality tool increases the cost of the tool, it reduces the overall processing cost while improving processing quality and efficiency.
Through this discussion of CNC lathe tools, we learned that tool types can be classified based on tool structure, manufacturing materials, and number of cutting edges. Tool selection occurs through human-machine interaction in the CNC machining process. As a crucial component in CNC lathe processing, the tool plays a significant role.
