Turning of large cylinders
Large hydraulic cylinders are key components in hydraulic systems and are widely used in engineering machinery, metallurgical equipment, and shipbuilding. Their large size, heavy weight, and high precision requirements make turning them challenging. Large cylinders typically consist of a cylinder barrel, base, and head, with the inner and outer diameters of the barrel being the primary focus of turning. Cylinder diameters typically range from 500 to 2000 mm, lengths can reach 5 to 10 meters, and weights can reach several or even tens of tons. High machining precision is required for large cylinders. The roundness error of the inner bore must be controlled within 0.03 to 0.05 mm, the cylindricity error must not exceed 0.05 to 0.1 mm/m, and the surface roughness must reach Ra 0.8 to 1.6 μm to ensure sealing performance and smooth movement. Furthermore, large cylinders are often made of structural alloy steels such as 27SiMn and 45 steel, and the blanks are often forgings or thick-walled steel pipes, resulting in significant machining allowances, presenting significant challenges for turning.
Equipment selection for turning large cylinders is fundamental to ensuring machining quality. A large lathe or floor-standing lathe with sufficient rigidity and power is essential. The spindle bore of a large lathe should be larger than the maximum diameter of the cylinder to facilitate workpiece insertion and clamping. For example, for machining a 1000mm diameter cylinder, a lathe with a spindle bore of at least 1100mm is required. The lathe’s guide rail length should be longer than the cylinder’s length to ensure the tool can fully feed. Floor-standing lathes are ideal for machining large cylinders. Their worktables can bear heavy loads and offer high rigidity and stability, making them suitable for machining heavy and long workpieces. Furthermore, the lathe’s CNC technology is crucial. CNC lathes can achieve automatic feed and dimensional control through program control, improving machining accuracy and efficiency while reducing human error. CNC lathes offer significant advantages for complex large cylinders, such as those with stepped bores and flanges.
The clamping method for large hydraulic cylinders directly impacts machining accuracy and safety. The appropriate clamping method should be selected based on the cylinder’s structure and weight. For shorter, lighter large cylinders, a three-jaw self-centering chuck and tailstock center can be used. The chuck holds one end of the cylinder, while the tailstock center supports the other. Adjusting the position of the chuck and center center ensures that the workpiece axis is aligned with the lathe spindle. For longer and heavier cylinders, auxiliary supports such as a steady rest or a steady rest are required. The steady rest is fixed to the lathe guide rails and supported in the center of the cylinder to minimize workpiece bending. The steady rest moves with the tool holder and supports the tool near the tool. It is suitable for machining cylinders with large aspect ratios. During clamping, excessive clamping force should be avoided, potentially leading to workpiece deformation. A dial indicator can be used to monitor the workpiece’s radial runout and adjust the runout to less than 0.05mm before proceeding. For thin-walled large cylinders, rigid supports or fillers can be used to enhance rigidity and prevent vibration and deformation during machining.
Tool selection and geometry design for turning large hydraulic cylinders must consider the requirements of large stock removal and high rigidity. Tool materials should be carbide or high-speed steel with excellent wear resistance and high strength. For machining high-strength alloy steels such as 27SiMn, carbide tools such as YT15 and YW1 are suitable. For rough turning, insert-type tools can be used to improve tool rigidity and heat dissipation. For finish turning, solid carbide or high-speed steel tools should be used to ensure surface quality. Regarding tool geometry, the rake angle should be 5°-10° to reduce cutting forces; the relief angle should be 6°-8° to ensure sharpness and heat dissipation; the lead angle should be 45°-60° to increase tool rigidity and reduce vibration; and the tool nose radius should be 1-2mm. A larger nose radius increases tool strength and is suitable for large stock removal. Furthermore, the tool shank should have a square or round cross-section for good rigidity and be short to avoid vibration during machining.
The cutting parameters and process measures for turning large cylinders need to be reasonably set according to the equipment performance, tool material, and workpiece material. During rough turning, to improve processing efficiency, a larger cutting depth and feed rate can be used. The cutting depth is generally 5-10mm, the feed rate is 0.3-0.5mm/r, and the cutting speed is 50-80m/min. During finish turning, to ensure processing accuracy and surface quality, the cutting depth is 0.5-1mm, the feed rate is 0.1-0.2mm/r, and the cutting speed is 80-120m/min. Adequate cooling and lubrication are required during processing. Due to the large machining allowances and high cutting heat of large cylinders, an emulsion with good cooling properties should be selected. The cutting fluid should be sprayed into the cutting area through a high-flow cooling system to reduce cutting temperature and tool wear. For processing the inner hole of the cylinder, a boring tool or internal turning tool can be used. The boring tool shank should have sufficient rigidity to avoid bending deformation during processing, which may affect the inner hole accuracy. The machining sequence should follow the principle of “exterior first, interior second, roughing first, finishing second.” Begin by machining the outer diameter and end faces, then use the machined outer diameter and end faces as a reference for machining the inner bore to ensure coaxiality. After machining, the cylinder’s inner and outer diameters require dimensional measurement and form and position tolerance testing. Tools such as inside and outside micrometers, micrometers, and dial indicators can be used. For cylindricity testing of long cylinders, laser interferometers or levels can be used to ensure that all accuracy indicators meet design requirements. High-quality turning of large cylinders can be achieved through appropriate equipment selection, clamping methods, tool parameters, and process measures.
