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Cutting inserts

In CNC machining, cutting inserts are one of the key elements that determine the efficiency and precision of the process. Learning about the different types of inserts, their uses, and specifications is essential for any CNC machine operator. Take a look at the following guide to help develop this topic. 

What are the types of cutting inserts? 

Cutting inserts are divided into different types. This division specifically relates to the material they are made, its shape, dimensions, and applications. The most common are turning inserts, groove-turning inserts, inserts for cutting hard materials, and thread-turning inserts. In addition, cutting inserts are available in many colors, which helps identify them.

Cutting inserts for turning and grooving

Turning inserts are one of the most versatile types of cutting inserts. They are used in various turning processes, such as: 

  • external turning, 
  • internal,
  • end turning or grooving.

Groove-turning inserts are specially designed for making precise grooves on workpieces. Their special geometry allows this cutting operation to be performed with precision.

Cutting inserts for hard materials

For hard materials such as stainless steel, titanium, and superalloys, the cutting inserts have special coatings and geometries that help reduce cutting forces and increase tool life.

Cutting insert markings

Cutting insert designations are essential for their proper selection in a specific cutting process. These markings follow the ISO standard and contain information on the insert's shape, dimensions, type, and cutting angles. For example, the designation "CNMG 120408" says that the inserts have a diamond shape, 80 degrees of angle, a diameter of 12.7 mm, and a thickness of 4.76 mm.

The geometry of Cutting Inserts

Cutting insert geometry is crucial to the quality and efficiency of the cutting process. Cutting insert geometry takes into account such aspects as:

  • insert shape, 
  • the angle of apposition, 
  • the angle of sharpening, 
  • yaw angle. 

Choosing the right geometry depends on many factors, such as: 

  • the type of material to be machined, 
  • the type of cutting operation, 
  • cutting parameters.
  • Multi-cutting insert 

Multi-edge inserts are special cutting inserts with more than one cutting edge on a single insert. Multi-point inserts can be used in the following ways:

  • lathe knives, 
  • milling heads,
  • other tools where multiple cutting is needed.

Multi-tool cutting tools are made of carbide. They are used for processing various metals and alloys. The material they are made is durable and resistant to high temperatures. They are often coated with additional layers to increase their performance and durability. The types of these tools depend on the shape (e.g., square, triangular) and are available in different sizes (according to ISO standards). Depending on needs, they can be reversed to utilize all cutting edges. When they are CVD coated, they are used for milling, turning steel in difficult conditions (NTP - 35), or machining gray cast iron (NTK - 25). PVD-coated inserts are used for notching classic and stainless steel (N-435) or machining these steels and surface-hardened materials (N-250). 

What factors to consider when selecting a cutting insert? 

The selection of cutting inserts is a critical factor in determining the success of any cutting process. When selecting a cutting insert, consider factors such as: 

  • the type of material being machined, 
  • the type of cutting operation, 
  • cutting parameters, 
  • surface quality requirements. 

Therefore, understanding cutting insert designations is key to proper insert selection. A typical CNC shop may use thousands of cutting inserts per year. An operator may use many cutting inserts daily without considering the complex science behind them. 

Types of cutting inserts 

In CNC (Computer Numerical Control), there are many cutting inserts, each with its specific application in machining different materials. Below are some common types:

  • Carbide inserts: These are the most commonly used cutting inserts. They are made of carbide, which is very hard and resistant to wear. Carbide inserts effectively machinate steel, cast iron, aluminum alloy, and plastics. Inserts made of this material have a resistance of up to 100 degrees. 
  • Ceramic inserts are characterized by high hardness, resistance to high temperatures, and chemical environmental factors. Ceramic inserts are often used for metalworking, especially in heavy cutting and high-speed machining. These types of inserts can withstand temperatures up to 1,200 degrees.
  • PCD inserts: PCD (Polycrystalline Diamond) are cutting inserts made of artificial diamond, the hardest known material. PCD inserts are mainly used for machining composites, plastics, aluminum, copper, and other materials with high thermal conductivity.
  • HSS inserts: HSS (High-Speed Steel) is a steel with high carbon, chromium, vanadium, and molybdenum content. HSS inserts are used for machining metals at higher cutting speeds. They are more flexible than carbide inserts but less resistant to wear.

It is worth remembering that the selection of the right cutting insert depends on the machined material type, cutting speed, depth of cut, and other factors. A suitably qualified CNC operator or metalworking engineer can advise on the best type of cutting insert for a particular job.

Cutting insert designation - ISO

International standards for selecting cutting inserts in CNC (computer-controlled machining machines) are important to ensure optimal, safe, and efficient cutting operations. ISO (International Organization for Standardization) defines such standards.ISO codes for cutting inserts to help identify their shape, angle, size, etc. Choosing the right cutting insert is crucial to the efficiency of the CNC machining process, and understanding and following ISO international standards can help optimize the process. An ISO code can have up to twelve symbols. The first seven are mandatory. The eighth and ninth are additional information that can be added if needed. Additional information about the manufacturer begins from the tenth to the twelfth symbol. These are added to the ISO code with a special character.

What do they mean in practice? The seven mandatory symbols tell about the shape of the tile, the angle of inclination, and other basic characteristics of the tile. Each symbol is a letter or number that uniquely identifies a particular insert. Special tables according to DIN4983 show what each letter in the code means. Additional information about the manufacturer is written after a special character. Depending on the company, these can tell you about the edge width, edge angle, cutting material, or chip breaker shape. You can find more detailed information regarding each ISO -> here. 

The role of insert geometry

When discussing the geometry of a cutting insert, most toolmakers immediately focus on macro-geometry or the physical shape of the insert. However, more and more attention is being paid to a fast-growing area of research, namely optimizing the micro-geometry of an insert's cutting edge. At the macro level, insert geometry optimization mainly focuses on creating the most effective shape for chip control. Different insert shapes and angles can produce the best results for breaking and removing chips from the cutting area depending on the workpiece material and machining method. Designing and optimizing insert macro geometries is already a fairly advanced area of technology, well mastered by most major cutting tool manufacturers. In practice, however, it is only in recent years that technology has advanced to the point where microscopic insert geometry can be controlled. Using advanced machining techniques, it is possible to create round, oval, or beveled cutting edges on the cutting surface of an insert and even introduce fine chamfers or grooves. Through various innovative technologies, it is possible to smooth and accurately measure the blade at the microscopic level, significantly improving the life and stability of the blade machining. Further technological advances can be expected to further develop this field and bring even more significant results.

How to choose the best cutting insert? 

Choosing the right cutting insert is crucial for optimal CNC machining performance. Cutting inserts, despite their small size, have a huge impact on the quality of the final product, machining speed, and tool life. So what should you pay special attention to? 

Type of machining 

The first step in insert selection is to understand the machining process. Will you be milling, turning, drilling, or doing another type of machining? Each of these processes requires a different type of cutting insert . Let's take a closer look at some of them:

  • Milling - Milling is a machining process that involves removing material by rotating a tool with multiple blades called a cutter. Depending on the milling operation, a different insert type may be required. For example, micro-grain carbide cutting inserts are often used for milling because of their fracture toughness and wear resistance.
  • Turning is a machining operation in which the workpiece material rotates, and the cutting insert moves linearly to remove the material. Typical turning inserts have a triangular or diamond shape, with different angles on the surfaces. The material of the turning insert depends on the type of workpiece material. For example, coated carbide inserts are often used for turning stainless steel.
  • Drilling - involves creating circular holes in the material. When choosing an insert for drilling, it is important to consider the hardness and strength of the workpiece material. Hard metal inserts, such as carbide, are often chosen for drilling hard materials.


Identifying the material to be machined

The next step is to identify the material to be machined. Different materials, such as steel, aluminum, titanium, or plastics, have different properties and require the right cutting inserts.

Selecting the right insert shape and size

The insert shape and size should be selected according to the type of machining and the CNC machine. Cutting inserts come in many shapes, such as squares, diamonds, triangles, and circle. The shape and size of the insert affect the machining quality and life of the insert.

Choosing the right insert material

The insert material is one of the most important factors to consider. Cutting inserts can be made of various materials, such as carbide, ceramic, polycrystalline diamond (PCD). The choice of insert material should depend on the workpiece material and performance requirements.

Choosing the right coating

The coating of a cutting insert can improve its performance and durability. There are different types of coatings, such as TiN (titanium nitride), TiCN (titanium nitride carbide), or Al2O3 (aluminum oxide). These coatings increase the insert's hardness and improve wear and temperature resistance.

Use of ISO standards

The International Organization for Standardization (ISO) has developed standards for classifying cutting inserts. The ISO standard for cutting inserts helps operators understand insert characteristics such as shape, size, clamping, material properties, and coating. We wrote more about this above. 

Consult with the tool manufacturer

Many cutting tool companies offer technical support and advice on cutting insert selection. Don't be afraid to take advantage of these resources. Experts from these companies have in-depth knowledge of their products and can help you make the best choice.

Experiment and optimize

Even after your initial insert selection, you should analyze its use in practice. CNC machining is a process of continuous improvement and optimization. Run tests, collect data, and adjust your choice based on results. You may find that different inserts are best for the different applications or machining conditions you perform. 

Concluding remarks

When you're choosing a cutting insert, you need to remember that not everything about it is immediately apparent. Without testing an insert on the job, it's hard to tell which is good and which is not. Choosing a cheap insert just because it looks similar to another may increase machining costs in the future. If you're unsure what type of tile to choose, it's a good idea to consult specialists in this tool. There are also some basic rules to help you narrow down your choice. Most manufacturers give their tiles numbers that tell you about their properties. To find the tiles you need, start by analyzing the catalog. Finally, if your tile isn't cutting as it should, there are some things you can look at to find a solution to the problem. Looking at the edge of the wafer through a magnifying glass may reveal the cause of the faulty cutting. If you notice that the edge is heavily worn or a bit bent, it's a sign that the tile is too soft, and you should choose a harder one. If, on the other hand, the edge of the insert is missing pieces, you should probably choose an insert that is less hard but more flexible. With the above information, you can make decisions that will improve the efficiency of your machining process and reduce its cost.