Carbide inserts are widely used in the metalworking industry for various machining operations, such as turning, milling, drilling, and boring. Carbide inserts offer superior performance, productivity, and tool life compared to other cutting materials, such as high-speed steel (HSS) or brazed carbide tools. However, not all carbide inserts are created equal. There are many factors to consider when selecting the right carbide insert for your specific machining application, such as:

  • The workpiece material and its machinability
  • The cutting speed, feed rate, and depth of cut
  • The tool geometry, such as shape, size, edge preparation, and nose radius
  • The coating type and thickness
  • The tool holder and clamping system

In this blog post, we will discuss some of the main aspects of carbide insert selection and provide some tips and recommendations to help you optimize your machining results.

Workpiece Material and Machinability

The first and most important factor to consider when choosing a carbide insert is the workpiece material and its machinability. Different materials have different properties, such as hardness, toughness, abrasiveness, thermal conductivity, and chemical reactivity, that affect the wear and failure modes of the cutting tool. For example, steel is generally harder and more abrasive than aluminum, but aluminum has higher thermal conductivity and lower chemical affinity with carbide. Therefore, different carbide grades and coatings are required for different materials to achieve the best balance between wear resistance and toughness.

The machinability of a material is a measure of how easy or difficult it is to machine with a given cutting tool. Machinability depends on various factors, such as the material composition, microstructure, hardness, strength, ductility, and surface condition. Machinability is often expressed as a percentage or a rating based on a standard material, such as free-cutting steel. The higher the machinability, the easier it is to machine the material with a high cutting speed, feed rate, and depth of cut, and the longer the tool life.

Generally, the machinability of a material decreases as its hardness and strength increase, and vice versa. However, there are some exceptions, such as cast iron, which has high hardness but also high machinability due to its graphite content. Some materials, such as stainless steel, titanium, and nickel-based alloys, are classified as difficult-to-cut materials, because they have low machinability and high tendency to cause tool wear and failure. These materials require special carbide grades and coatings that can withstand high temperatures, pressures, and chemical reactions at the cutting edge.

Cutting Speed, Feed Rate, and Depth of Cut

The second factor to consider when choosing a carbide insert is the cutting speed, feed rate, and depth of cut. These are the main parameters that determine the cutting conditions and the material removal rate in a machining operation. They also affect the temperature, pressure, and stress at the cutting edge, and thus the tool wear and failure modes.

The cutting speed is the linear velocity of the cutting edge relative to the workpiece surface. It is usually expressed in meters per minute (m/min) or surface feet per minute (sfm). The cutting speed depends on the workpiece material, the tool material, the tool geometry, and the coating type. Generally, the higher the cutting speed, the higher the productivity and the lower the tool life, and vice versa. However, there is an optimal cutting speed range for each material and tool combination, where the tool life is maximized and the tool wear is minimized. This optimal cutting speed range can be determined by conducting cutting tests or consulting the manufacturer’s recommendations.

The feed rate is the linear distance that the cutting edge advances into the workpiece per revolution of the spindle or per tooth of the tool. It is usually expressed in millimeters per revolution (mm/rev) or inches per revolution (ipr) for turning, and in millimeters per tooth (mm/tooth) or inches per tooth (ipt) for milling. The feed rate depends on the workpiece material, the tool material, the tool geometry, and the coating type. Generally, the higher the feed rate, the higher the productivity and the material removal rate, but also the higher the cutting forces and the tool wear, and vice versa. However, there is an optimal feed rate range for each material and tool combination, where the surface finish and the dimensional accuracy are optimized and the tool wear is minimized. This optimal feed rate range can be determined by conducting cutting tests or consulting the manufacturer’s recommendations.

The depth of cut is the perpendicular distance that the cutting edge penetrates into the workpiece. It is usually expressed in millimeters (mm) or inches (in). The depth of cut depends on the workpiece material, the tool material, the tool geometry, and the coating type. Generally, the higher the depth of cut, the higher the productivity and the material removal rate, but also the higher the cutting forces and the tool wear, and vice versa. However, there is an optimal depth of cut range for each material and tool combination, where the tool life and the tool stability are maximized and the tool wear and vibration are minimized. This optimal depth of cut range can be determined by conducting cutting tests or consulting the manufacturer’s recommendations.

Tool Geometry

The third factor to consider when choosing a carbide insert is the tool geometry, such as shape, size, edge preparation, and nose radius. The tool geometry affects the cutting performance, the surface finish, the dimensional accuracy, and the tool life of the insert.

The shape of the insert determines the number of cutting edges, the chip formation, and the chip evacuation. There are various insert shapes available, such as triangular, square, rhombic, round, and irregular. Each shape has its own advantages and disadvantages, depending on the machining operation and the workpiece geometry. For example, triangular inserts have three cutting edges and can be used for turning, grooving, and threading operations. However, they have a small clearance angle and a weak cutting edge, which limit their application to light and medium machining. Square inserts have four cutting edges and can be used for turning, milling, and face milling operations. However, they have a large clearance angle and a strong cutting edge, which make them suitable for heavy and interrupted machining.

The size of the insert determines the strength, the stability, and the cutting forces of the tool. The size of the insert is usually expressed by two parameters: the inscribed circle diameter (IC) and the thickness (T). The IC is the diameter of the largest circle that can be inscribed within the insert shape. The T is the distance between the top and bottom surfaces of the insert. Generally, the larger the size of the insert, the stronger and more stable the tool, but also the higher the cutting forces and the power consumption, and vice versa. Therefore, the size of the insert should be selected according to the machining requirements and the machine capabilities.

The edge preparation of the insert determines the sharpness, the wear resistance, and the toughness of the cutting edge. The edge preparation is the modification of the cutting edge geometry by grinding, honing, or coating. There are various edge preparations available, such as sharp, honed, chamfered, and radiused. Each edge preparation has its own advantages and disadvantages, depending on the workpiece material and the cutting conditions. For example, sharp edges have low cutting forces and high surface finish, but also low wear resistance and high tendency to chip or fracture. Honed edges have high wear resistance and high toughness, but also high cutting forces and low surface finish. Chamfered edges have a compromise between sharp and honed edges, with moderate cutting forces, wear resistance, and surface finish. Radiused edges have a smooth transition between the rake and flank faces, which reduces the stress concentration and improves the tool life.

The nose radius of the insert determines the surface finish, the dimensional accuracy, and the tool life of the tool. The nose radius is the radius of the arc at the tip of the insert. Generally, the larger the nose radius, the better the surface finish and the dimensional accuracy, but also the higher the cutting forces and the tool wear, and vice versa. Therefore, the nose radius of the insert should be selected according to the surface finish and dimensional accuracy requirements of the workpiece.

Coating Type and Thickness

The fourth factor to consider when choosing a carbide insert is the coating type and thickness. The coating is a thin layer of hard and wear-resistant material that is applied on the surface of the carbide substrate by physical or chemical vapor deposition (PVD or CVD) methods. The coating enhances the performance and the tool life of the insert by providing:

  • Higher hardness and wear resistance
  • Lower friction and adhesion
  • Higher thermal and chemical stability
  • Higher oxidation and corrosion resistance

There are various coating materials available, such as titanium carbide (TiC), titanium nitride (TiN), titanium carbonitride (TiCN), aluminum oxide (Al2O3), and diamond-like carbon (DLC). Each coating material has its own advantages and disadvantages, depending on the workpiece material and the cutting conditions. For example, TiC has high hardness and wear resistance, but also high brittleness and low thermal stability. TiN has low friction and adhesion, but also low hardness and wear resistance. TiCN has a compromise between TiC and TiN, with moderate hardness, wear resistance, friction, and adhesion. Al2O3 has high thermal and chemical stability, but also high friction and adhesion. DLC has low friction and adhesion, but also low thermal and chemical stability.

The thickness of the coating determines the balance between the wear resistance and the toughness of the insert. Generally, the thicker the coating, the higher the wear resistance,