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Analysis on the Processing Technology and Problems of the Hole in Supporting Hydraulic Cylinder
In the field of hydraulic cylinder manufacturing, ensuring the reliability and precision of components is essential for overall system performance. One critical component is the support cylinder, which plays a vital role in crane operations. The precision machining of its parts directly affects the safety and efficiency of the entire system. As shown in Figure 1, the cylinder block consists of welded joints and flange plates, made from 45 steel. The workpiece has an inner diameter of Ø210mm, an outer diameter of Ø300mm, and a length of 740mm. Due to the small bore size, traditional boring methods face challenges such as poor chip evacuation, heat dissipation, and tool wear, making the process more complex.
During the inner hole machining process, several issues often arise, including misalignment of the centerline, uneven wall thickness, and surface roughness that fails to meet specifications. These problems are primarily due to the limitations of the boring bar's rigidity and the difficulty in maintaining consistent cutting conditions throughout the operation. To address these challenges, a well-planned machining sequence is essential, starting with rough turning, welding, and annealing, followed by precise boring and rolling.
The selection of the process benchmark is crucial for achieving dimensional accuracy and uniform wall thickness. The flange surface and center frame base are used as references for subsequent operations, ensuring consistency in the machining process. Stress relief annealing is also necessary after welding to reduce internal stresses and prevent deformation during further processing.
In the deep hole drilling and boring process, the TZ120A machine is employed, with clamping methods as illustrated in Figure 2. Proper cooling and lubrication are vital, as the small through-holes in the boring bar must efficiently deliver coolant to the cutting area while facilitating chip removal. The chips should ideally be C-shaped for easier evacuation.
For rough and semi-finished boring, a cemented carbide tool with a 75° main cutting edge angle is used to minimize radial forces and increase cutting speed. The cutting parameters are adjusted based on the bore size and material properties. For example, during rough boring, the machine speed is set at 30 r/min, feed rate at 7.5 mm/min, and cutting depth at 1.5 mm, resulting in an inner diameter of approximately Ø218 mm. Semi-finishing follows with a slightly higher feed rate and reduced cutting depth to approach the final dimensions.
One major issue encountered is the uneven wall thickness caused by slight displacement of the boring bar due to poor rigidity. This results in a deviation of up to 0.10 mm at the entrance, leading to a wall thickness difference of 0.20 mm. To resolve this, the guide sleeve gap is reduced to 0.02 mm, ensuring better alignment and minimizing wall thickness variations.
Another challenge is the discrepancy in end sizes after semi-finishing. This occurs because measurements are not taken during the cutting process, and the exit end may exceed tolerance limits. A solution is to align the boring bar and tool head precisely to avoid angular deflection, which can cause larger deviations at the exit end.
To achieve the required surface finish and precision, a floating boring process is implemented using an adjustable boring tool. As shown in Figure 4, the tool features a guide block made of nylon, which provides elasticity and prevents surface scratching. The guide block is slightly oversized to allow automatic adjustment during machining, maintaining accurate guidance.
After floating boring, the rolling process is performed to enhance surface quality and ensure dimensional stability. The rolling interference is kept within 0.02–0.04 mm, using an adjustable ball roller. The first rolling is done at 70 r/min with a feed rate of 15 mm/min, followed by a second pass at 7.5 mm/min to reduce waviness and improve surface finish. Lubrication and cooling during rolling are similar to those in fine boring, ensuring optimal tool performance and surface quality.
In conclusion, this paper presents a comprehensive and feasible machining process for the support cylinder of a hydraulic cylinder. By addressing key challenges such as tool wear, wall thickness variation, and surface roughness, the proposed method ensures high-quality machining and meets the technical requirements of the design. This approach serves as a valuable reference for the production of similar hydraulic cylinder components.