The hydraulic support is a critical component in ensuring the safe and efficient operation of coal mines, serving as essential heavy-duty equipment for underground mining activities. Its performance and durability directly impact both the safety of the mine and the production of raw coal. At the core of this system lies the hydraulic jack, which is responsible for the movement and control of the support structure. The reliability, flexibility, and safety of the entire support system depend largely on the quality of the jack's manufacturing. If the sealing performance of the piston and piston rod is compromised, fluid leakage, pressure loss, and even serious safety hazards can occur.
The lifespan of the hydraulic support is heavily influenced by the quality of the hydraulic jack. The piston and piston rod are key components that determine the jack’s longevity. During machining, the surface roughness and cylindricity of the sealing groove are crucial. A high surface roughness at the bottom of the groove can lead to rapid wear of the sealing elements, resulting in ineffective sealing, fluid leakage, and reduced support performance.
**Cause Analysis**
Traditionally, grooved workpieces were machined using conventional grooving tools. These tools typically produced surface roughness values between Ra 6.3 and 3.2 μm, which met basic requirements. However, for parts like the piston and piston rod in hydraulic jacks, where the sealing groove requires a surface roughness of Ra 1.6–3.2 μm and a tolerance level of Js8, achieving consistent precision becomes challenging. Conventional tools often struggle with maintaining the required cylindrical accuracy and surface finish, leading to several issues:
1. When multiple grooves with varying widths need to be machined, aligning multiple grooving tools increases setup time. This includes additional measurements and tool adjustments, which also increase the time spent on size control during the cutting process.
2. Equal-width forming tools tend to be too wide, causing increased radial cutting forces and vibration, which negatively affects surface roughness, cylindricity, and roundness.
3. Using smaller grooving tools than the groove width leads to residual material on the workpiece after retraction, potentially causing chipping or sticking due to excessive back force and insufficient machining allowance.
4. Wear or chipping on the main cutting edge of the tool can leave convex marks on the groove bottom, further degrading the surface quality.
**Tool Improvement Measures and Advantages**
To address these challenges, an improved concave double-tip, double-edge grooving tool was developed. This tool retains the original shape of a standard grooving tool but modifies the main cutting edge to have a slight concave arc in the center. This creates two wiper tips and two side cutting edges, allowing for precise machining with only a 0.05–0.01 mm radial machining allowance. It prevents hair pulling, knife sticking, built-up edge formation, vibration, and ripple effects.
Key advantages include:
1. Suitable for various groove widths, reducing the need for frequent tool changes and setup times.
2. Enables radial machining of wide grooves with a small margin left, followed by axial cutting to avoid vibrations.
3. Allows for precise radial feeding to achieve the desired groove width, especially when the tool is smaller than the groove.
4. Helps remove any convex marks caused by tool wear or chipping through axial feeding.
This improved tool offers significant benefits: it is ideal for batch production, supports multiple groove widths on a single part, eliminates the need for rotating the tool holder, simplifies dimensional control, reduces vibration and sticking, and ensures high-quality surface finish. It is particularly well-suited for use on CNC machines.
After testing 260 types of piston rods, the improved tool demonstrated superior performance. It achieved twice the efficiency of traditional tools, ensured a 100% pass rate, reduced defect rates by 30%, and lowered scrap rates to 4%. When used on CNC machines, manual tool positioning was minimized, boosting productivity to 40 pieces per shift—four times faster than with conventional tools.
In conclusion, the use of this advanced concave multi-blade grooving tool significantly reduces production costs and enhances profitability. For example, producing 260 φ80mm piston rod parts generated a profit of 50,000 yuan. Additionally, it helped the company save 10 million yuan by avoiding outsourcing, filling a critical gap in their production capabilities.
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