**Abstract:**
An on-line electrolytic dressing technique was introduced for precision mirror grinding of metal-bonded superabrasive grinding wheels. This method enabled the production of a steel mirror cemented carbide with a mirror surface having a roughness ranging from 0.003 μm to 0.011 μm. The process offers shaping and high efficiency, making it a viable alternative to the conventional multi-stage grinding approach.
**Keywords:** steel-bonded carbide; ELID grinding; precision mirror surface grinding; base metal grinding wheel
**DOI:** TG580.613; TG743
**Document code:** A
**Article ID:** 1004-132X(2000)03-0288-02
**1. Challenges in Grinding Steel-Bonded Carbide**
Steel-bonded carbide is manufactured using tool steel or alloy steel as the binder phase, combined with refractory metal carbides such as WC or TiC through powder metallurgy. Its microstructure features fine and hard particles dispersed within the steel matrix. The hard phase provides high hardness and wear resistance, while the steel binder ensures toughness and machinability. However, this combination makes the material difficult to machine, especially during precision operations.
During grinding, the steel matrix tends to wear away more easily than the hard carbide grains, leading to uneven surface removal. This results in the formation of pores on the surface, which can trap swarf and cause rapid wheel clogging and thermal damage. Traditional methods often result in low surface quality, inefficient multi-step processes, and high costs.
To address these issues, an on-line electrolytic dressing (ELID) technique using ultra-fine diamond or CBN wheels has been developed. This method achieves a surface roughness of around 10 nm, significantly improving both efficiency and surface finish. It allows for precise mirror-like finishing of steel-bonded carbide, overcoming the limitations of conventional approaches.
**2. Principles of ELID Grinding Technology**
ELID grinding, developed in Japan in the early 1990s, is an advanced ultra-precision machining method. It utilizes cast iron or iron fiber-bonded diamond or CBN wheels, where anodic dissolution occurs during electrolysis. A DC pulse power supply and a weak electrolyte solution are used to control the process.
In this method, the cast iron wheel acts as the anode, forming an Fe₂O₃ oxide layer on its surface. This layer prevents excessive material removal while allowing sharp abrasive grains to protrude. As the wheel wears, the oxide film is scraped off by the workpiece, triggering further electrolysis and self-repair. This cyclical process maintains the wheel’s sharpness and extends its life, ensuring consistent grinding performance.
**3. Application of ELID to Steel-Bonded Cemented Carbide**
**3.1 Test Conditions**
The test involved a MM7120 grinding machine, W1.5 (CIB-D) diamond and CBN mixed abrasive iron-based grinding wheels, a homemade HDMD-II ELID power supply, and HDMY-201 electrolytic grinding fluid. The parameters included spindle speeds of 1,500 rpm, feed rates between 0.1–3 mm/stroke, and a grinding depth of 0.001–0.005 mm. Electrolytic voltage ranged from 90–105 V, with current between 1–3 A and electrode clearance of 0.1–0.75 mm.
**3.2 Grinding Results and Analysis**
Under these conditions, the steel-bonded carbide achieved a mirror finish with Ra values between 0.003 μm and 0.011 μm. Using finer abrasives (W1 or smaller) could further reduce Ra. The surface roughness was influenced not only by abrasive type and size but also by the composition of the grinding fluid.
Experiments showed that different fluids produced varying surface qualities. While HDMY-110 and HDMY-200 worked well on materials like optical glass and sapphire, they were ineffective on steel-bonded carbide. Adjusting the fluid composition and abrasive type allowed for optimal performance, achieving better surface finish and lower Ra values.
**4. Conclusion**
ELID mirror grinding technology enables the production of high-quality mirror surfaces on steel-bonded carbide, achieving roughness levels in the order of 10 nm. This technique replaces traditional multi-step grinding with a more efficient, cost-effective, and high-quality process. It represents a promising advancement in precision machining, offering improved performance and broader application potential.
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