CNC Machining of Large Alloy Steel Screws
Large alloy steel lead screws are key components in mechanical transmissions and are widely used in large machinery such as machine tools, lifting equipment, and precision instruments. Their CNC machining quality directly impacts the transmission accuracy and service life of these equipment. CNC Machining is a key process in the CNC machining of large alloy steel lead screws. Due to the high strength, toughness, and cutting resistance of alloy steel, as well as the large size and poor rigidity of large lead screws, turning presents numerous challenges, requiring the appropriate selection of cutting tools, precise cutting parameters, and effective process management.
Before turning large alloy steel lead screws, thorough preparation is required. First, the blank must be inspected, including its material, size, and straightness, to ensure it meets the processing requirements. Large alloy steel lead screw blanks are typically made using a forging process. While the internal structure of the forged blank is relatively dense, it may contain internal stress. Therefore, heat treatment, such as annealing or normalizing, is required before turning to eliminate internal stress, reduce material hardness, and improve cutting performance. At the same time, a detailed turning process plan, including processing sequence, clamping method, and tool selection, must be developed based on the lead screw’s precision requirements and structural characteristics.
Tool selection is a critical step in turning large alloy steel lead screws. Due to the high hardness and strength of alloy steel, ordinary high-speed steel tools are difficult to meet cutting requirements, so carbide or ceramic tools are typically used. Carbide tools offer high hardness and wear resistance, can withstand high cutting forces, and are suitable for rough and semi-finishing turning operations. Ceramic tools offer higher hardness and better wear resistance, making them suitable for high-speed finishing, but are more brittle and require care to avoid impact during use. Tool geometry also requires rational design, with the rake and clearance angles adjusted to the material properties of the alloy steel to minimize cutting resistance and tool wear.
The determination of cutting parameters has a significant impact on the turning quality and efficiency of large alloy steel lead screws. Cutting speed, feed rate, and cutting depth are the three main cutting parameters that need to be considered comprehensively. Excessively high cutting speeds will lead to accelerated tool wear and even tool burning; while excessively low cutting speeds will reduce processing efficiency. For large alloy steel lead screws, a lower cutting speed, a larger feed rate, and a larger cutting depth should be used during rough turning to quickly remove excess material; while a higher cutting speed, a smaller feed rate, and a smaller cutting depth should be used during fine turning to ensure surface quality and dimensional accuracy. At the same time, it is also necessary to rationally select the cutting fluid. The cutting fluid not only cools the tool and workpiece, but also lubricates the cutting surface, reducing friction and wear. Commonly used cutting fluids include emulsions and cutting oils.
The clamping method and CNC machining process are also crucial to the turning accuracy of large alloy steel lead screws. Due to their long length and poor rigidity, large lead screws are prone to bending and deformation during the turning process, so a reasonable clamping method is necessary. Common clamping methods include double-thimble clamping and single-clamp, single-thimble clamping. For extra-long lead screws, a steady rest or center rest is required to increase workpiece rigidity and prevent vibration and deformation during CNC machining. The CNC machining process should follow the principle of “roughing first, finishing second, exterior first, interior second.” After rough turning, aging treatment is performed to eliminate CNC machining stresses, followed by semi-finishing and finish turning to ensure the ultimate accuracy of the lead screw. In addition, during the turning process, it is necessary to measure the workpiece dimensions in a timely manner and adjust the cutting parameters based on the measurement results to ensure that the dimensional accuracy of the lead screw meets the requirements.
