The structure and selection of turning tools
A turning tool is the primary tool used for cutting workpieces in lathe machining. Its structure and selection directly impact machining quality, efficiency, and tool life. A turning tool consists of a tool head and a tool shank. The tool head performs the cutting work, while the tool shank mounts the tool on the lathe toolholder, ensuring stability during the cutting process. Structural parameters of a turning tool include geometric angles, cutting edge shape, and tool head dimensions. A reasonable structural design can reduce cutting forces, lower cutting temperatures, and improve cutting performance. In actual production, a turning tool must be selected scientifically based on factors such as the workpiece material, machining requirements, and lathe performance to achieve high-quality, efficient, and low-cost machining.
Turning tools can be categorized into four types based on the connection between the cutter head and the tool shank: integral, welded, machine-clamped, and indexable. Integral turning tools are made from a single piece of high-speed steel or carbide, with the cutter head and tool shank integrated. This simple structure offers excellent rigidity, but low material utilization, and is primarily used for high-speed steel tools and small turning tools. Welded turning tools, with carbide inserts welded to a 45 steel tool shank, offer lower costs and can be ground to various geometric angles according to processing requirements, making them suitable for single-piece, small-batch production. However, the welding process can easily generate internal stress, leading to insert cracking. Machine-clamped turning tools mechanically secure the insert to the tool shank, making the insert replaceable and the tool shank reusable, reducing tool material waste and making them suitable for medium-volume production. Indexable turning tools utilize a blade with multiple cutting edges mounted to the tool shank via a clamping device. When a cutting edge wears, a new one can be accessed by simply rotating the blade, significantly improving tool change efficiency. This makes them suitable for mass production and automated processing, and they are currently the most widely used turning tool structure.
The geometric angle of the turning tool is the key parameter that affects the cutting performance, mainly including the rake angle, clearance angle, main deflection angle, secondary deflection angle and cutting edge inclination angle. The rake angle is the angle between the front cutting edge and the base surface, and its size affects the cutting deformation and cutting force. When processing plastic materials (such as 45 steel), the rake angle is 15°-20°, and when processing brittle materials (such as cast iron), the rake angle is 5°-10°. The rake angle of carbide turning tools is generally 5°-10° smaller than that of high-speed steel turning tools; the clearance angle is the angle between the rear cutting edge and the cutting plane, and its function is to reduce the friction between the rear cutting edge and the workpiece. It is generally 6°-12°, and a larger value is used for fine processing and a smaller value is used for rough processing; the main deflection angle affects the distribution of cutting force and tool life. Commonly used main deflection angles are 45°, 60°, and 90°. When processing slender shafts, 90° is used to reduce radial force, and 45° is used when processing workpieces with good rigidity. To improve tool life; the secondary rake angle is used to reduce the friction between the secondary flank and the machined surface, generally 5°-10°, and a smaller value is taken when high surface roughness requirements are required; the blade inclination angle controls the flow direction of the chips, a positive blade inclination angle makes the chips flow to the surface to be machined, and a negative value makes them flow to the machined surface. It is 0°-5° for fine machining and -5°–10° for rough machining.
The selection of turning tools requires comprehensive consideration of factors such as the workpiece material, machining stage, and machining accuracy. When machining plastic materials such as low-carbon and medium-carbon steels, carbide turning tools with high wear resistance and red hardness, such as YT15 and YT30, should be selected to avoid built-up edge. When machining brittle materials such as cast iron and bronze, YG-type carbide turning tools with increased toughness, such as YG6 and YG8, are recommended to prevent insert breakage. When machining difficult-to-machine materials such as stainless steel and high-temperature alloys, YW-type general-purpose carbide or coated carbide turning tools are recommended to maximize tool life. Regarding the machining stages, roughing operations require tools with high rigidity and strength, such as welded turning tools with a 45° lead angle, to withstand the higher cutting forces. Finishing operations require tools with high precision and sharp cutting edges, such as indexable finishing tools, to ensure surface quality. For workpieces requiring precision above IT7, high-speed steel turning tools are also recommended for final cutting to achieve a low surface roughness.
The installation and sharpening of turning tools also significantly impact their performance. When installing a turning tool, ensure the tool head extends an appropriate length (generally no more than 1.5 times the toolholder diameter) to avoid vibration during cutting. The tool tip should be aligned with the lathe spindle axis within a tolerance of 0.1mm, otherwise the tool’s actual geometry will be altered. The tool should be securely connected to the toolholder using multiple screws to prevent loosening during machining. When sharpening a turning tool, adjust the various geometric angles according to machining requirements to ensure a sharp cutting edge and a smooth surface. Carbide turning tools are sharpened with a diamond grinding wheel, while high-speed steel turning tools are sharpened with an alumina grinding wheel. Cooling is required after sharpening to prevent overheating and annealing. Furthermore, turning tools will wear over time. When the flank wear reaches 0.5-1mm, the blade should be reground or replaced promptly to ensure consistent machining quality. Through rational structural design, scientific selection, and proper use and maintenance, turning tools can achieve optimal performance in lathe machining, providing strong support for mechanical manufacturing.
