Machining of stainless steel sleeves
Stainless steel sleeves are essential components commonly used in machinery manufacturing, widely used in bearing housings, hydraulic systems, pipe connections, and other applications. Compared to ordinary steel, stainless steel sleeves offer high strength, corrosion resistance, and toughness, but they also present challenges such as increased machining difficulty, rapid tool wear, and high cutting temperatures. When turning stainless steel sleeves, a rational machining process, along with appropriate tooling and cutting parameters, must be developed based on the material’s properties and structural characteristics to ensure dimensional accuracy, surface quality, and production efficiency.
The turning of stainless steel sleeves must first address the material’s processing characteristics. The thermal conductivity of stainless steel is approximately 1/3 that of ordinary carbon steel. The heat generated during the cutting process is difficult to dissipate, resulting in an increase in the temperature of the cutting zone, which can easily increase tool wear and even cause tool sticking. At the same time, stainless steel has good plasticity and high elongation. During cutting, the chips are not easy to break, and they are prone to forming long and tough ribbon-like chips. These chips will not only entangle the tool and workpiece, affecting the smooth progress of processing, but may also scratch the processed surface. In addition, the work hardening phenomenon during stainless steel processing is severe, and the hardness of the surface metal can increase by 50%-100%, making subsequent processing difficult and shortening the tool life. Therefore, before turning stainless steel sleeves, it is necessary to fully understand these characteristics and take targeted measures, such as selecting the appropriate tool material, optimizing the tool angle, and using cutting fluid reasonably.
Tool selection is a critical step in turning stainless steel sleeves. Tool materials should possess high hardness, wear resistance, and red hardness to withstand high temperatures and high cutting forces. Common tool materials include carbide and high-speed steel, with carbide being the most widely used. When machining stainless steel, YG-type carbides (such as YG6 and YG8) offer excellent toughness and impact resistance, making them suitable for machining stainless steels with high plasticity. YW-type carbides (such as YW1 and YW2) are general-purpose carbides that combine the advantages of both YG and YT types, offering both impact resistance and high wear resistance, making them suitable for machining a variety of stainless steels. For finishing stainless steel sleeves requiring high precision, high-speed steel tools (such as W18Cr4V) can also be used to achieve a better surface quality through low-speed cutting. In terms of tool geometry parameters, the rake angle should be a larger value (10°-20°) to reduce cutting deformation and cutting force; the back angle should be 8°-12° to reduce the friction between the back tool face and the workpiece; the main rake angle should be 45°-75°, which is conducive to heat dissipation and reducing radial force; the blade inclination angle should be -5°-0° to allow the chips to flow to the surface to be processed of the workpiece to avoid scratching the processed surface.
The choice of clamping method depends on the structure and size of the stainless steel sleeve. For short, thick stainless steel sleeves, a three-jaw self-centering chuck can be used for direct clamping. During clamping, copper pads should be placed between the jaws and the workpiece to protect the workpiece surface and increase friction. For stainless steel sleeves with a larger aspect ratio, a clamping and supporting method should be used to prevent bending and deformation during machining. This method uses a three-jaw chuck to clamp one end and a tailstock center to support the other end. This method, combined with a steady rest or tool rest, enhances workpiece rigidity. For thin-walled stainless steel sleeves, axial clamping or a dedicated fixture should be used to avoid excessive radial clamping force that could cause workpiece deformation. For example, a mandrel and a nut can be used for axial clamping. The outer diameter of the mandrel is used to locate the inner hole of the stainless steel sleeve, and the nut applies axial clamping force to ensure uniform force on the workpiece and minimize deformation. During clamping, pay attention to the clamping force to ensure that the workpiece does not loosen while avoiding deformation caused by excessive clamping.
The reasonable setting of cutting parameters has a great influence on the turning quality and efficiency of stainless steel sleeves. Cutting speed is the main factor affecting cutting temperature and tool wear. When processing stainless steel, the cutting speed should not be too high, otherwise it will cause the cutting temperature to rise sharply and aggravate tool wear. When using carbide tools to turn stainless steel sleeves, the cutting speed is generally controlled at 80-150m/min; when using high-speed steel tools, the cutting speed is lower, usually 10-30m/min. The selection of feed rate should be determined according to the surface roughness requirements and tool life. The feed rate can be 0.2-0.4mm/r during roughing to improve processing efficiency; the feed rate should be reduced to 0.1-0.2mm/r during fine processing to obtain better surface quality. The back cutting amount is determined according to the processing allowance. It can be 2-5mm during roughing to quickly remove the allowance; it is 0.5-1mm during fine processing to ensure dimensional accuracy. In addition, the use of cutting fluid is very important for the turning of stainless steel sleeves. Cutting fluid with good cooling, lubrication and rust prevention properties should be selected, such as extreme pressure emulsion or sulfurized cutting oil. By continuously spraying cutting fluid, the cutting temperature can be reduced, tool wear can be reduced, and surface quality can be improved.
Quality control during the machining process is an important measure to ensure the quality of stainless steel sleeves. During the turning process, the wear of the tool should be checked frequently. If the tool is severely worn, it should be replaced or sharpened in time to avoid affecting the machining accuracy and surface quality. After each process is completed, the dimensions of the workpiece need to be measured, such as using a vernier caliper or micrometer to measure the inner and outer diameters, length and other dimensions, and using a dial indicator to check the form and position tolerances such as roundness and coaxiality. If the dimensions are found to be out of tolerance, the cutting parameters or clamping method should be adjusted in time to ensure that subsequent machining meets the requirements. For stainless steel sleeves with higher precision requirements, aging treatment can be performed after rough turning to eliminate internal stress, and then fine turning can be performed to ensure the dimensional stability of the parts. In addition, after machining is completed, the surface of the stainless steel sleeve needs to be cleaned and inspected to remove burrs and oil stains, and to ensure that the surface is free of defects such as scratches and cracks to meet the requirements of use.
