A square hole is to be cut using ECM through a plate of low alloy steel that is

Question

A square hole is to be cut using ECM through a plate of low alloy steel that is 12 mm thick. The specific removal rate for this steel is 3.7 by 10^-2 mm^3/A-s. The hole is 35 mm on each side, but the electrode used to cut the hole is slightly less than 35 mm on its sides to allow for overcut, and its shape includes a hole in its center to permit the flow of electrolyte and to reduce the area of the cut. This tool design results in a frontal area of 245 mm^2. The applied current = 1200 amps, (a) Using an efficiency of 95%, how long will it take to cut the hole? (b) If the tool were designed with a frontal area equal to the hole size, how long will it take to cut the hole?

Explanation / Answer

(a) Given that specific emoval rate, C = 3.7 x 10-2 mm3/A-s

MRR, fr = CI/A = (3.7 x 10-2 mm3/A-s)(1200 A)/(245 mm2) = 0.18122 mm/s

At 95% efficiency, fr = 0.95*(0.18122 mm/s) = 0.17216 mm/s

Time to machine = (12 mm)/(0.17126 mm/s) = 69.7 s

(b) Given that specific emoval rate, C = 3.7 x 10-2 mm3/A-s

MRR, fr = CI/A = (3.7 x 10-2 mm3/A-s)(1200 A)/(35*35 mm2) = 0.036244 mm/s

At 95% efficiency, fr = 0.95*(0.036244 mm/s) = 0.03443 mm/s

Time to machine = (12 mm)/(0.03443 mm/s) = 348.5 s

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