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.

The Rockwell hardness test has multiple scales, each designated by a specific letter. The most common scales are Rockwell A (HRA), Rockwell B (HRB), Rockwell C (HRC), and Rockwell D (HRD). Each scale uses a different combination of the indenter and the applied load.

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.

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:

So now that we know about what hardness means for your part and how you can obtain hardness whilst simultaneously retaining a part’s toughness, let’s talk about testing a part’s hardness. How you test a part’s hardness and the methods that are available.

Rockwell tends to be the most commonly used way of testing hardness, due to its speed and simplicity. It is also suitable for a wide range of materials including metals, plastics and ceramics. The Rockwell test offers several different scales (A,B,C etc.) based on different combinations of indenter types and applied loads.

Hardness and toughness are normally inversely proportional to each other e.g. glass is hard, but it’s low toughness makes it very fragile. Plastics are often tough, but not as resistant to surface and impact damage as metals.

ISOturning insertnomenclature

The Brinell test is typically used for materials with a coarse or granular microstructure, such as cast iron, aluminium, and soft metals. It provides a reliable measurement of hardness but may not be suitable for very hard or thin materials due to the large indentation size.

Plating, coating or surface heat treatment often aim to provide the hard and/or hard-wearing surfaces required, whilst maintaining the materials’ inherent toughness.Hard anodising is available at Protolabs, our digital network, also offer heat treatment and painting, learn more here.

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.

This method is commonly used for on-site testing and is useful for large and heavy components. It is less accurate than the Brinell, Rockwell, or Vickers tests but offers the advantage of quick measurements without the need for sample preparation.

Quenching is a process used to rapidly cool a heated metal or alloy to enhance its mechanical characteristics. During the process the metal or alloy is heated to a high temperature to allow for changes in its atomic structure. It is then quickly cooled down, often by immersing the part into water, oil or exposing it to cool air/steam. This “quenching” locks in the changes to the structure that occurred during the heating process. The result, parts with very high hardness. To control the resulting hardness a tempering process may be used. Tempering prolongs the service life of the part, reducing brittleness.

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

There are many methods of heat treating a part to potentially make it harder. These include quenching, precipitation hardening (ageing), case hardening and carburising, which are offered through our digital network.

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 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.

It's important to note that the Rockwell hardness scales are dimensionless numbers and are used to represent the hardness of a material based on the depth the indenter penetrates the material. The higher the Rockwell hardness number, the harder the material. Additionally, different Rockwell scales are used for different types of materials, so it's essential to specify the scale being used when reporting Rockwell hardness values.

Machininginsertnomenclature

This method is suitable for a wide range of materials, including metals, ceramics, and plastics. Due to its small indentation size the Vickers hardness test allows for testing on very thin materials and provides accurate results.

Do you need a guide for selecting thermoplastic materials? Here you will find expert knowledge about thermoplastics and tips that will make it easier for you to choose a material for your moulded parts.

Triangle carbideInsertsizes

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

For HBS a hardened steel ball was/is used to determine the value. This is used for materials with a value below 450 such as mild steel and grey cast iron, however, the HBS method isn’t really used any longer, although it is sometimes still referred to.HBW indicates a cemented carbide ball is used. This is used for materials with a value below 650. As HBW is the only method still used it is often expressed as simply HB on datasheets.

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?

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:

Carbonitriding – A combination of carburising and nitriding. The part is exposed to an atmosphere containing both carbon and nitrogen. This creates a surface layer rich in both carbon and nitrogen compounds.

Carbide inserts chart

Thin steel, case-hardened steel, shallow case-hardened steel, cemented carbide, other materials with relatively low hardness

At Protolabs the majority of our datasheets include figures utilising the Brinell and Rockwell hardness tests, please see below for a selection metals we offer at Protolabs for CNC machining and their hardness values. For other materials, please check the numbers provided on our material datasheets found here. Or if unsure, please speak to one of our application engineers by phone +(0) 1952 683047 or email [email protected]

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).

The Leeb hardness value is a dimensionless number, and it is usually converted to different scales to represent the hardness of the material in specific units, such as HRC (Rockwell C hardness) or HB (Brinell hardness).

KennametalTurning insertGrade chart

Also known as surface hardening. This heat treatment is used to improve the hardness and wear resistance of the metal’s surface, whilst retaining the toughness of its inner core. This method is particularly useful for components that need to withstand abrasive wear, impact, and other forms of mechanical stress. The metal’s surface layer composition is altered through diffusion.

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:

Carburising – the most common of the methods. The metal part is heated in an environment that is rich in carbon, which causes the carbon atoms to diffuse into the surface layer. The result is a surface layer high in carbon, which can be hardened through subsequent quenching (rapid cooling).

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.

The Leeb hardness test is a non-destructive and portable method used primarily for metals. It involves a spring-loaded end with a spherical or conical indenter. The end that makes contact with the material is released, and the rebound velocity is measured after striking the material's surface. The Leeb hardness value is then determined based on the ratio of the rebound velocity to the impact velocity.

Precipitation hardening is also known as age hardening and is used to strengthen certain types of alloys, in particular those based on aluminium, magnesium, and some steels. The treatment itself is a three-step process, a combination of solution treatment (solutionising) and ageing.  During the first step the alloy is heated to a high temperature (also known as the solution treatment stage) it is generally heated to just below its melting point. This high heat allows metal atoms and alloying elements to dissolve into a solid solution. This treatment basically homogenises the alloy’s composition. Reducing any segregation of elements.The second step is quenching (rapidly cooling) to hold the alloy’s new microstructure.Before finally being heated at a lower temperature for a long-time (ageing). During the ageing process the alloying elements begin to separate from the solid solution. They form microscopic precipitates (particles) within the material structure. These precipitates hinder the movement of structural defects (dislocations) within the crystal lattice of the material. Consequently, impeding plastic deformation and improving strength and hardness.There are two stages within the ageing process, nucleation and growth. At the beginning, during nucleation, small clusters of precipitate atoms begin to form with the alloy’s matrix (nucleation). Nucleation sites can include crystal defects, grain boundaries, and other imperfections. During the “growth” stage and once nucleation has occurred, the precipitates grown in size and number. Then continue to hinder the movement of dislocations, effectively strengthening the material.

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.

The Vickers hardness test utilises a diamond pyramid-shaped indenter to create a small impression on the material's surface. Taking into consideration the weight of the load, the size of the indentation is measured using a microscope. The Vickers hardness number (HV) is calculated based on the indentation diagonal lengths.

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 Rockwell hardness test is based on the indentation depth caused by a diamond or a ball indenter under different loads. There are two main scales used in the Rockwell test: the Rockwell HRC scale (uses a diamond cone indenter) for harder materials and the Rockwell HRB scale (uses a ball indenter) for softer materials.

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.

Nitriding – Like carburising the metal part is heated in an environment, but this time rich in not just carbon, but also nitrogen. Nitrogen atoms diffuse into the surface, forming nitrides, which increases the hardness and wear resistance. Particularly effective for use on stainless steel and other alloyed steels.

Milling inserttypes

Induction Hardening – the surface layer of the metal part is heated using high-frequency induction heating, and then the part is quenched.  The localised heating and quenching result in a hardened surface, whilst retaining core properties.

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.

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.

Insertnose radius chart

Hard anodised parts are tested for hardness using the Vickers test. On average, hard anodised aluminium 6082 can achieve values in the range of 300 to 500 HV, to put that into perspective, in its untreated state it has a hardness range of 80-95 HV. Exact hardness is entirely dependent on process parameters, such as anodising time, temperature, voltage and electrolyte composition. It’s also important to note that hardness may not be uniform across the entire material.

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.

Flame Hardening – a high-temperature flame is directed onto the surface of the metal part, followed by quenching. Similar to induction hardening this method only hardens the surface layer.

The Leeb hardness test is commonly used for on-site hardness measurements, especially in large and heavy components, where other conventional hardness tests might be impractical or not feasible. However, it's important to note that the Leeb hardness test might not be as accurate as other laboratory-based hardness tests (e.g., Brinell, Rockwell, or Vickers) and might be affected by factors such as surface roughness and material homogeneity. Calibration and standardisation are critical to obtaining reliable and accurate hardness values using the Leeb hardness test method.

Hard materials resist deformation, indentation or scratches making them harder wearing, longer lasting and often easier to clean and maintain.

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

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 are the different types of case hardening?There are several different methods of case hardening, they include, carburising, nitriding, carbonitriding, induction hardening and flame hardening. Out digital network offers carburising.

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.

A thin, protective coating is applied to the aluminium part, forming a protective oxide layer. This layer creates a barrier against corrosion. There is the choice of decorative anodising and hard anodising. Hard anodising is the most durable anodising finish available on machined aluminium parts.

Carbideinsertidentification chart PDF

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.

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.

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.

The hardness of a material refers to the materials ability to resist deformation, indentation or scratches. It is a measure of the materials hardness. There are several different tests used to display the hardness of materials including, Brinell (HB), Rockwell (HRC), Vickers (HV)and Leeb.

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

The Brinell hardness test is named after its inventor, Johan August Brinell. It involves applying a constant load or force to a spherical indenter made of hardened steel or carbide onto the surface of the material being tested. The indentation diameter is then measured optically. The Brinell hardness number (BHN) is calculated as the load applied divided by the surface area of the indentation.