Turning of deformed high temperature alloy threaded sleeve
Deformed high-temperature alloy threaded sleeves are widely used in high-end equipment fields such as aerospace and petrochemicals because they can maintain good mechanical properties under high temperature, high pressure and corrosive environments. However, their turning processing faces many challenges. Deformed high-temperature alloys have the characteristics of high hardness and high strength. The hardness can reach 300~400HB at room temperature, and the strength decreases slowly as the temperature rises. This greatly increases the cutting force during turning, which is usually 2~3 times that of ordinary steel. At the same time, the material has excellent plasticity and toughness. Severe tool sticking is prone to occur during turning, forming built-up edge, which not only affects the surface quality of the thread, but also aggravates tool wear. In addition, the thermal conductivity of deformed high-temperature alloys is extremely low, only 1/5~1/10 of that of 45 steel. The cutting heat is difficult to dissipate and accumulates in the cutting area, resulting in excessive tool temperature, reducing the tool life and cutting performance.
Given the turning characteristics of deformed superalloy threaded sleeves, the appropriate selection of cutting tools is crucial. Commonly used cutting tool materials include ceramic, cubic boron nitride (CBN), and coated carbide. Ceramic cutting tools offer high hardness and wear resistance, can withstand high cutting temperatures, and are suitable for high-speed turning. However, they are brittle and have poor impact resistance, making them unsuitable for roughing or interrupted cutting. CBN cutting tools, second only to diamond in hardness, offer excellent wear and heat resistance, and can maintain stable cutting performance at high temperatures, making them ideal for machining deformed superalloys, especially for finish turning. However, their cost is relatively high. Coated carbide cutting tools, by applying a wear-resistant coating such as TiAlN or AlCrN to the carbide substrate, significantly improve the tool’s wear and heat resistance, achieving a balanced balance between cost and performance. They are widely used in rough and semi-finish turning of deformed superalloy threaded sleeves. Tool geometry should be designed to reduce cutting forces and heat. The rake angle is generally between -5° and 0°, and the relief angle is between 8° and 12° to enhance tool strength and heat dissipation.
Optimizing cutting parameters significantly impacts the turning quality and efficiency of deformed high-temperature alloy threaded sleeves. The selection of cutting speed requires comprehensive consideration of the tool material and machining stage. When using CBN tools for finish turning, the cutting speed can be controlled between 80 and 120 m/min. When using coated carbide tools for rough turning, the cutting speed should be reduced to 30 to 50 m/min to prevent excessive tool wear. The feed rate should be determined based on the thread’s required accuracy. Rough turning can use a higher feed rate (0.2 to 0.3 mm/r) to improve machining efficiency; finish turning requires a lower feed rate (0.1 to 0.15 mm/r) to ensure surface roughness and dimensional accuracy. The depth of cut should be selected gradually. For rough turning, the depth of cut can be controlled at 1 to 2 mm per turn to gradually remove excess material; for finish turning, the depth of cut should be reduced to 0.1 to 0.3 mm to reduce surface residual stress. In addition, the selection and supply method of cutting fluid cannot be ignored. Extreme pressure cutting oil or water-based cutting fluid should be used, and the cutting fluid should be precisely sprayed into the cutting area through a high-pressure cooling system to effectively reduce the cutting temperature and reduce tool wear.
Controlling the turning process of deformed high-temperature alloy threaded sleeves is a key step in ensuring machining quality. During the rough turning stage, a large cutting depth and feed rate should be used to quickly remove excess material from the blank, while also taking care to avoid tool damage due to excessive cutting forces. After rough turning, the workpiece needs to be aged to eliminate machining stress and prevent deformation during subsequent processing. During semi-finishing turning, cutting parameters should be adjusted according to the thread precision requirements, gradually improving the dimensional accuracy and surface quality of the workpiece in preparation for finishing. When finishing threads, high-precision thread turning tools should be used, with strict control of cutting speed and feed rate to ensure that the thread profile, pitch, and mean diameter meet design standards. During the turning process, the tool should be regularly inspected and sharpened to prevent tool wear from affecting thread quality. Furthermore, attention should be paid to the workpiece clamping method, using dedicated fixtures or center positioning to ensure the workpiece is stable and reliable during turning and reduce the impact of vibration on machining accuracy.
After turning, quality inspection and subsequent processing of deformed high-temperature alloy threaded sleeves are essential. First, the dimensional accuracy of the threads, including parameters such as pitch, pitch diameter, and thread angle, is checked using tools such as thread gauges and vernier calipers to ensure they meet design requirements. For sleeves with higher precision requirements, a comprehensive three-dimensional coordinate measuring machine (CMM) is also required. Next, the surface quality of the threads is inspected for defects such as cracks, scratches, and tool sticking. Any defects require prompt repair or rework. Sleeves with substandard surface quality are prone to stress concentration during use, affecting their service life and safety. Furthermore, the sleeves must be cleaned and deburred to remove oil, chips, and burrs from the surface, improving their surface finish. Finally, the sleeves are subjected to necessary heat treatments, such as solution treatment and aging treatment, to further enhance their mechanical properties and ensure stable operation in high-temperature and high-pressure environments. Through rigorous quality inspections and scientific post-processing, the processing quality and performance of deformed high-temperature alloy threaded sleeves can be effectively guaranteed.
