In CNC machining, cutting inserts are one of the key elements that determine the efficiency and precision of the process. Understanding the different types of inserts, their applications, and specifications is essential for every CNC machine operator. We invite you to familiarize yourself with the guide below, which will help to expand on this topic.
What are the types of cutting inserts?
Cutting inserts are divided into various types. This division particularly concerns the material they are made of, shape, dimensions, and applications. Most often, you can list turning inserts, grooving inserts, hard material cutting inserts, and thread turning inserts. In addition, cutting inserts are available in many colors, which helps in their identification.
Turning and grooving cutting inserts
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 or grooving.
Grooving inserts are specially designed for making precise grooves in machined parts. Their unique geometry allows for accurate performance of such cutting operations.
Cutting inserts for hard materials
For hard materials, such as stainless steel, titanium or superalloys, cutting inserts have a special coating and geometry that help to reduce cutting forces and increase tool life.
Cutting insert designations
The markings of cutting inserts are essential for their proper selection in a specific cutting process. These markings are in accordance with ISO standards and contain information about the shape, dimensions, type, and cutting angles of the insert. For example, the marking "CNMG 120408" indicates that the inserts are diamond-shaped, have an 80-degree angle, a diameter of 12.7 mm, and a thickness of 4.76 mm.
Geometry of Cutting Inserts
The geometry of the cutting insert is crucial for the quality and efficiency of the cutting process. The geometry of the cutting insert takes into account aspects such as:
- shape of the insert,
- approach angle,
- sharpening angle,
- deviation angle.
The choice of the appropriate geometry depends on many factors, such as:
- type of material being processed,
- type of cutting operation,
- cutting parameters.
Multi-edge insert
Multi-edge inserts are a special type of cutting inserts that have more than one cutting edge on a single insert. Multi-edge inserts can be used in:
- turning tools,
- milling heads,
- other tools where multiple cutting is needed.
Multi-edge cutting tools are made of sintered carbide. They are used for processing various metals and alloys. The material they are made of is durable and resistant to high temperatures. They are often covered with additional layers, increasing their performance and durability. The types of these tools depend on the shape (e.g. square, triangular) and they are available in various sizes (according to ISO standards). Depending on the needs, they can be reversed to utilize all cutting edges. In case of their CVD coating, they are used for milling, turning steel in difficult conditions (NTP - 35), or processing gray cast iron (NTK - 25). Plates, which are coated with the PVD method, are used for cutting classic and stainless steel (N-435), or processing these steels and materials that are surface hardened (N-250).
What factors to consider when choosing a cutting insert?
The selection of cutting inserts is a critical factor in the success of any cutting process. When choosing a cutting insert, you should consider factors such as:
- type of material being processed,
- type of cutting operation,
- cutting parameters,
- surface quality requirements.
Therefore, understanding the markings of cutting inserts is key to proper insert selection. A typical CNC workshop can consume thousands of cutting inserts each year. The operator may use multiple cutting inserts daily, without giving much thought to the complex science behind them.
Types of cutting inserts
In CNC (Computer Numerical Control), there are many types of cutting inserts, each with its specific application in the machining of various materials. Below we present a few popular types:
- Carbide inserts: These are the most commonly used cutting inserts. They are made of sintered carbides, which are very hard and resistant to wear. Carbide inserts are effective in machining materials such as steel, cast iron, aluminum alloy and plastics. Inserts made of this material are resistant up to 100 degrees.
- Ceramic tiles: Characterized by high hardness, resistance to high temperatures and environmental chemical factors. Ceramic tiles are often used for metal processing, especially during heavy cutting and high-speed processing. This type of tiles can withstand temperatures up to 1200 degrees.
- PCD Inserts: PCD (Polycrystalline Diamond) are cutting inserts made from synthetic diamond, which is 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 metal machining at higher cutting speeds. They are more flexible than carbide inserts, but less resistant to wear.
It's worth remembering that the choice of the appropriate cutting insert depends on the type of material to be machined, cutting speed, depth of cut, and other factors. A properly qualified CNC operator or metalworking engineer will be able to advise on the best type of cutting insert for a specific task.
Cutting insert designation - ISO
International standards for the selection of cutting inserts in CNC (Computer Numerically Controlled machining) are crucial to ensure optimal, safe, and efficient cutting operations. ISO (International Organization for Standardization) defines such standards. ISO codes for cutting inserts help identify their shape, angle, size, etc. Choosing the right cutting insert is key to the efficiency of the CNC machining process, and understanding and adhering to international ISO standards can contribute to optimizing this process. The 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. From the tenth to the twelfth symbol, additional manufacturer information begins. They are added to the ISO code using a special character.
What do they mean in practice? Seven mandatory symbols indicate the shape of the insert or the angle of inclination, as well as other basic features of the insert. Each symbol is a letter or a number that uniquely identifies a particular insert. There are special tables according to DIN4983 standard, which show what each letter in the code means. Additional information about the manufacturer is recorded after a special character. Depending on the company, they can talk about the width of the edge, the edge angle, the cutting material, or the shape of the chip breaker. You can find more detailed information about individual ISOs -> here.
Role of the tile geometry
When we talk about the geometry of a cutting insert, most tool-making companies immediately focus on macro-geometry, that is, the physical shape of the insert. However, more and more attention is being paid to the rapidly developing field of research, which is the optimization of the micro-geometry of the cutting edge of the insert. At the macro level, the optimization of the insert geometry mainly focuses on creating the most effective shape for chip control. Depending on the material being machined and the machining method, using different shapes and angles of inserts can give the best results in terms of breaking and removing chips from the cutting area. Designing and optimizing the macro-geometry of inserts is already a fairly advanced area of technology, well mastered by most major cutting tool manufacturers. However, in practice, only the last few years have brought the development of technology to the point where it is possible to control the microscopic geometry of the insert. Using advanced machining techniques, cutting edges of a round, oval or oblique shape can be created on the cutting surface of the insert, and even minor chamfers or grooves can be introduced. Thanks to the use of various innovative technologies, it is possible to smooth and accurately measure the blade at the microscopic level, which has significantly improved the lifespan and stability of blade machining. It can be expected that further technological advances will contribute to further development of 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. Despite their small size, cutting inserts 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 choosing a cutting insert is understanding the machining process to be performed. Will you be milling, turning, drilling, or performing 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 mill. Depending on the milling operation, a different type of insert may be required. For example, micro-grain cemented carbide cutting inserts are often used for milling due to their fracture toughness and wear resistance.
Turning - Turning is a machining process in which the workpiece is rotating, and the cutting tool moves linearly, removing material. Typical turning inserts have a triangular or rhomboidal shape, with various inclination angles on the surfaces. The material of the turning insert depends on the type of workpiece material. For example, for turning stainless steel, inserts made of sintered carbide with a coating are often used.
Drilling - involves creating round holes in the material. When choosing a drill bit, it is important to consider the hardness and durability of the material being processed. Hard metal bits, such as tungsten carbide, are often chosen for drilling hard and durable materials.
Identification of the material to be processed
The next step is to identify the material to be processed. Different materials, such as steel, aluminum, titanium, or plastics, have different properties and require the use of appropriate cutting inserts.
Selection of the appropriate shape and size of the insert
The shape and size of the insert should be selected depending on the type of machining and the CNC machine. Cutting inserts come in many shapes, such as square, diamond, triangle, or circle. The shape and size of the insert affect the quality of machining and the durability of the insert.
Choosing the right insert material
The material of the insert is one of the most important factors to consider. Cutting inserts can be made from various materials, such as sintered carbides, ceramics, polycrystalline diamonds (PCD), and others. The choice of insert material should depend on the material being machined and performance requirements.
Choosing the right coating
The coating of the cutting insert can improve its performance and durability. There are various types of coatings, such as TiN (titanium nitride), TiCN (titanium carbonitride) or Al2O3 (aluminum oxide). These coatings increase the hardness of the insert, 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 the characteristics of the insert, such as shape, size, mounting, material properties, and coating. We wrote more about this above.
Consultations with the tool manufacturer
Many companies producing cutting tools offer technical support and advice on the selection of cutting inserts. 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 making the initial choice of the tile, you should analyze its use in practice. CNC machining is a process of continuous improvement and optimization. Conduct tests, collect data, and adjust your choice based on actual results. It may turn out that different tiles are best for different applications or machining conditions you are conducting.
Final Remarks
When choosing a cutting insert, you must remember that not everything in it is visible at once. Without testing the insert in work, it is hard to say which one is good and which is not. Choosing a cheap insert just because it looks similar to another one, we may increase the processing costs in the future. If you are not sure which type of insert to choose, it is worth consulting with specialists in this type of tools. There are also some basic rules that will help you narrow down your choice. Most manufacturers assign numbers to their inserts, which tell about their properties. To find the inserts you need, start by analyzing the catalog. Finally, if your insert does not cut as it should, there are certain things you can pay attention to in order to find a solution to this problem. Looking at the edge of the insert through a magnifying glass may reveal the cause of faulty cutting. If you notice that the edge is heavily worn or slightly bent, it's a sign that the insert is too soft and you should choose a harder one. If, on the other hand, there are pieces missing from the edge of the insert, 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 the machining process and reduce its costs.