Project ForgeThe surface irregularities of the tool and work-piece electrodes used in an electrochemical machining (ECM) process are 6 μm and 3 μm respectively (peaks reducing the nominal inter-electrode gap toward each other). The work-piece is pure iron, and 12V DC is applied between the electrodes. Conductivity of the electrolyte = 0.02 ohm⁻¹mm⁻¹, over-potential voltage = 1.5V, density of iron = 7860 kg/m³, atomic weight of iron = 55.85 g, valence = 2, Faraday constant = 96500 C. The largest feed rate is __________ mm/min.
Explanation
The largest feed rate occurs at the minimum instantaneous gap, y = sum of the two surfaces' peak irregularities = 6+3 = 9 μm = 0.009 mm. Effective voltage = 12-1.5=10.5V. Current density J=κ·V_eff/y=0.02×10.5/0.009≈23.33 A/mm². Gram-equivalent E=A/(zF)=55.85e-3/(2×96500)≈2.894e-7 kg/C. Feed rate f=J·E/ρ = 23.33×2.894e-7/7.86e-6 mm/s ≈ 0.859 mm/s ≈ 51.5 mm/min.
Source: GATE ME 2016 Set-2 (2016)
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