Practical process parameters and tools for stainless steel turning
Stainless steel, with its excellent corrosion and oxidation resistance and mechanical properties, has been widely used in machinery manufacturing, chemical equipment, medical devices and other fields. However, the turning of stainless steel faces many challenges due to its material properties, such as severe work hardening, high cutting temperatures, and rapid tool wear. Therefore, mastering practical process parameters and tool selection techniques for stainless steel turning is crucial to improving processing efficiency and ensuring processing quality. In actual production, the rationality of process parameters and the adaptability of tools directly affect the stability of the turning process and the precision of the final product, and need to be scientifically determined based on the specific type of stainless steel and processing requirements.
Cutting speed is one of the primary process parameters to consider when turning stainless steel, significantly affecting cutting temperature, tool wear, and machined surface quality. For commonly used stainless steel materials such as austenitic stainless steel, due to their poor thermal conductivity, excessively high cutting speeds can lead to a sharp increase in cutting temperature, exacerbating tool wear and even causing tool sticking. Excessively low cutting speeds, on the other hand, can reduce machining efficiency and potentially cause work hardening due to increased cutting forces. Generally speaking, when turning austenitic stainless steel with carbide tools, the cutting speed should be controlled between 80 and 150 m/min. If high-speed steel tools are used, the cutting speed should be reduced to 15 to 50 m/min to avoid tool damage from overheating. Furthermore, for harder materials such as martensitic stainless steel, the cutting speed needs to be further reduced, typically within the range of 50 to 100 m/min. The specific value needs to be refined based on the workpiece’s dimensional accuracy and surface quality requirements.
The selection of feed rate and depth of cut is also a key factor in setting process parameters for stainless steel turning. Excessive feed rates increase cutting forces and torque, leading to workpiece deformation, increased vibration, and even tool damage. Excessive feed rates prolong machining time, reduce productivity, and may also generate high cutting heat due to increased friction between the tool and the workpiece surface. In practice, the feed rate for stainless steel turning is typically set between 0.1-0.3 mm/r. For workpieces requiring high surface quality, the feed rate can be reduced to 0.05-0.15 mm/r. The depth of cut should be determined based on the workpiece’s stock size and the machining stage. For roughing, a larger depth of cut, typically 2-5 mm, is recommended to quickly remove excess material. For finishing, a smaller depth of cut, typically between 0.1-0.5 mm, should be used to ensure machining accuracy and surface finish. It is important to note that the feed rate and depth of cut should be aligned with the cutting speed to form a reasonable cutting parameter system to avoid adversely affecting machining results due to improper parameter combinations.
The choice of tool material plays a crucial role in the success of stainless steel turning. Different tool materials exhibit varying wear resistance, heat resistance, and adhesion resistance, requiring targeted selection based on the type of stainless steel and processing conditions. Carbide tools are the preferred tool material for stainless steel turning due to their high hardness, wear resistance, and good heat resistance. Tungsten-cobalt-titanium (YT) carbide is suitable for machining austenitic stainless steels with good plasticity, but exhibits slightly poor adhesion resistance. Tungsten-cobalt (YG) carbide, with its superior toughness and adhesion resistance, is more suitable for machining martensitic stainless steels and applications subject to impact loads. In recent years, coated carbide tools, such as TiN and TiAlN coated tools, have gained widespread adoption. Their surface coating significantly improves tool wear resistance and oxidation resistance, effectively reducing tool adhesion and extending tool life, demonstrating excellent performance in stainless steel turning. For high-precision, high-surface-quality stainless steel turning, ceramic and cubic boron nitride (CBN) tools are also suitable. However, be aware of their brittleness and suitability for high-speed, low-feed cutting conditions.
Reasonable design of tool geometry parameters can effectively improve the cutting performance of stainless steel, reduce cutting force and cutting heat, and improve processing quality. The rake angle is one of the most important parameters in tool geometry. For stainless steel turning, due to the high plasticity of the material and severe work hardening, a larger rake angle should be selected, generally 10°-20°, to reduce cutting deformation and cutting force, and reduce cutting temperature. The choice of the back angle should take into account the wear of the tool, usually 5°-10°. A larger back angle can reduce the friction between the tool back face and the machined surface of the workpiece and improve the surface quality, but too large a back angle will reduce the strength of the tool. The selection of the main rake angle and the secondary rake angle needs to be determined according to the shape of the workpiece and the processing requirements. The main rake angle is generally 45°-90° to reduce radial cutting force and avoid workpiece deformation; the secondary rake angle is usually 5°-15° to reduce the residual area of the machined surface and improve the surface finish. In addition, the tool nose radius also affects cutting force and surface quality. When turning stainless steel, the tool nose radius is generally 0.4-1.2mm. A smaller tool nose radius can reduce cutting force and vibration, but an excessively large tool nose radius can increase cutting heat and surface roughness. By optimizing tool geometry parameters, the tool can achieve optimal performance in stainless steel turning, achieving efficient and high-quality processing results.
