Indexable inserts for cutting tools
Indexable inserts for cutting tools are core components in modern metal cutting. Mechanically clamped to the cutter body, they offer advantages such as easy replacement, high cutting efficiency, and stable tool life. They have widely replaced traditional welded cutting tools and become the mainstream cutting tool for CNC machine tools and machining centers. The advent of indexable inserts has dramatically changed the production model of the metalworking industry, reducing tool change time from the traditional 30 minutes to 1-2 minutes, effectively improving overall equipment efficiency (OEE). These inserts are typically manufactured from superhard materials such as cemented carbide, ceramics, cubic boron nitride (CBN), and diamond. They are precision pressed and sintered, and have standardized geometric parameters and installation dimensions, enabling interchangeability between products from different manufacturers, reducing users’ inventory costs and management difficulties.
The geometric design of indexable inserts directly impacts cutting performance and machining quality. Insert geometric parameters include the normal rake angle (γₙ), clearance angle (αₙ ) , lead angle (κᵣ ) , cutting edge inclination angle (λₛ ) , and nose radius ( rε ). These parameters must be optimized based on the material being machined, the cutting method, and the machining requirements. For example, when machining plastic materials like aluminum alloys, a larger rake angle ( 10°-15° ) is used to reduce cutting forces and built-up edge. When machining high-strength steel, a smaller rake angle ( 0°-5° ) or even a negative rake angle ( -5° to -10° ) is used to enhance cutting edge strength. Lead angles are typically available in various options, including 45° , 75° , and 90° . Inserts with a 90° lead angle are suitable for machining stepped surfaces and right-angled shoulders, while inserts with a 45° lead angle offer more uniform cutting force distribution and are suitable for machining slender shafts. The tool tip radius significantly impacts surface roughness and tool life. A small radius (0.2-0.4mm) is used for finishing to achieve low Ra values, while a large radius (0.8-1.6mm) is used for roughing to enhance edge strength. An aircraft engine manufacturer achieved a 30% increase in cutting efficiency and a 50% extension in tool life for Inconel 718 alloy by optimizing insert geometry.
The model coding system for indexable inserts is key to achieving standardization and interchangeability. The International Organization for Standardization (ISO) has established unified insert model coding rules, and my country has also formulated the corresponding standard GB/T 2076-2007. This 10-digit code consisting of letters and numbers represents the insert’s shape, size, thickness, hole type, accuracy, cutting direction, clearance angle, rake angle, and nose radius. For example, in the insert model “CNMG120408-PM,” “C” indicates a diamond-shaped insert (80° vertex angle), “N” indicates a 0° clearance angle, “M” indicates the accuracy grade (medium accuracy), “G” indicates a round hole and chip breaker, “12” indicates an insert side length of 12.7mm, “04” indicates a thickness of 4.76mm, “08” indicates a nose radius of 0.8mm, and “PM” indicates the tool material grade. This coding system allows users to quickly and accurately select the required inserts while ensuring interchangeability between inserts of the same model from different manufacturers, greatly facilitating tool management and procurement.
The materials and coating technology used for indexable inserts are crucial for improving cutting performance. Insert materials must possess high hardness, high wear resistance, sufficient toughness, and heat resistance. Commonly used materials include: tungsten-cobalt carbide ( WC-Co ), suitable for machining cast iron and non-ferrous metals; tungsten-titanium-cobalt carbide ( WC-TiC-Co ), suitable for machining steel; ceramics ( Al₂O₃ , Si₃N₄ ), suitable for high-speed machining of cast iron and high-temperature alloys; CBN , suitable for machining hardened steel ( HRC50 and above); and PCD , suitable for machining non-ferrous metals and non-metallic materials. To further enhance performance, the insert surface is typically coated with a wear-resistant coating using physical vapor deposition ( PVD ) or chemical vapor deposition ( CVD ) techniques, such as TiN (titanium nitride), TiCN (titanium carbonitride), or AlTiN (aluminum titanium nitride). The coating thickness typically ranges from 3-10μm. AlTiN coatings offer excellent oxidation resistance at high temperatures, making them suitable for high-speed cutting (speeds > 300 m/min). Their wear resistance is 3-5 times that of uncoated inserts. An automotive transmission manufacturer used AlTiN-coated WC-TiC-Co inserts to machine 20CrMnTi gears, increasing tool life from 30 to 80 pieces per blade and reducing machining costs by 40%.
The clamping method and chipbreaker design of indexable inserts are crucial to machining stability. The clamping method must ensure that the insert does not loosen or shift under cutting forces. Commonly used methods include screw clamping, lever clamping, and wedge clamping. Lever clamping offers fast tool changes and high positioning accuracy (repeatability error ≤ 0.01mm), making it widely used in CNC tools. Clamping components (such as screws and washers) should be made of high-strength alloys (such as 40CrNiMo) and tempered (HRC 35-40) to prevent deformation or breakage. The shape and size of the chipbreaker are designed according to the cutting material and parameters, and can be linear, curved, or broken-line. Their function is to control chip curling, breakage, and discharge, preventing chips from wrapping around the tool or scratching the workpiece surface. When machining steel, wide and deep chipbreakers (5-8mm width, 1-2mm depth) are used to handle continuous chips. When machining cast iron, narrow and shallow chipbreakers are used to handle broken chips. A precision machinery manufacturer has improved the chip handling efficiency of 304 stainless steel by 60% by optimizing the chip breaker design, thus avoiding machining interruptions caused by chip accumulation.
