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Analysis on the Processing Technology and Problems of the Hole in Supporting Hydraulic Cylinder
In the context of hydraulic cylinder manufacturing, the support cylinder plays a critical role in ensuring the stability and safety of cranes during lifting operations. The precision of machining for these components is extremely high, especially for parts such as the cylinder block, which consists of welded joints and flange plates. As illustrated in Figure 1, the cylinder block is made from 45 steel, with an inner diameter of Ø210mm, outer diameter of Ø300mm, and a length of 740mm. Due to its small bore size, the boring bar used is thin, leading to challenges in chip removal, heat dissipation, and tool wear. Therefore, careful selection of machining processes is essential.
During the inner hole machining process, several issues can arise, including misalignment of the bore centerline, uneven wall thickness, and inconsistent diameters at both ends of the cylinder. Additionally, the surface roughness may not meet the required standards. To address these problems, a well-defined process plan is necessary. This includes steps such as rough center frame base preparation, coarse turning of the outer and inner surfaces, welding of flanges, drilling of holes, and subsequent annealing to relieve internal stresses caused by welding.
The key operation in this process is the precision boring and rolling of the inner hole. For this, the flange surface and the center frame base are used as reference points to ensure accurate alignment. A TZ120A deep hole drilling and boring machine is employed, with proper clamping methods to secure the workpiece (as shown in Figure 2). Cooling and lubrication are also crucial, as they help manage heat and improve chip removal efficiency.
In rough and semi-finished boring, a cemented carbide tool with a 75° main cutting edge angle is used to reduce radial force and increase cutting speed. Parameters such as spindle speed, feed rate, and depth of cut are carefully controlled to maintain dimensional accuracy. However, due to the low rigidity of the boring bar, minor displacements can occur, leading to deviations in the bore centerline and uneven wall thickness. To resolve this, the guide sleeve gap should be reduced to approximately 0.02mm, minimizing tool deflection and improving wall thickness uniformity.
Another issue arises when one end of the workpiece meets the required dimensions while the other is oversized. This is often due to measurement limitations during the semi-finishing stage. To prevent this, it is important to align the boring bar’s centerline with the boring head to avoid any angular deviation that could cause uneven bore sizes. As shown in Figure 3, using an adjustable floating boring tool after semi-finishing helps achieve more consistent results. This tool has a small back angle and a flat wiper, allowing it to apply a squeezing action that improves surface finish to Ra 1.6 μm and achieves IT7 level precision.
The guide block in the floating boring tool is typically made of nylon, providing elasticity to avoid scratching the workpiece surface while maintaining guidance. Adjusting the guide block slightly larger than the workpiece size allows for automatic wear during the process, ensuring continued accuracy. In practice, the first floating boring is performed at 30r/min with a feed rate of 15mm/min and a cutting depth of 0.2mm, achieving a bore size of Ø219.9±0.01mm. The second pass, a fine boring operation, uses a slower feed rate of 7.5mm/min and a cutting depth of 0.05mm, resulting in a final size of Ø220+0.03+0.05mm.
Rolling is then applied to further refine the inner surface. An adjustable ball roller is used with an interference of 0.02–0.04mm. Proper rolling parameters, such as a first pass at 70r/min with a feed of 15mm/min, followed by a second pass at 7.5mm/min, help eliminate waviness and improve surface quality. Lubrication and cooling during rolling are similar to those used in fine boring, ensuring optimal performance.
In conclusion, through detailed analysis of the machining process, including roughing, semi-finishing, finishing, and rolling, a reliable and efficient method for producing hydraulic cylinder bores has been established. This approach not only ensures dimensional accuracy but also enhances surface quality, making it a valuable reference for similar hydraulic cylinder manufacturing processes.