The flat surface of a large cast iron part measuring $1.5 m \times 0.6 m \times 0.25 m$ is to be machined on planer. The cutting speed is 21 m/min, return speed is 42 m /min, feed is 2 mm/ stroke, time for reversing the table is 0.02 min. Approach and over travel are 20 mm each, machining allowance on either side of plate width is 5.5 mm. The planning time will be _______ s. (Correct to-one decimal place)

2386.8

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Solution

The correct option is A 2386.8
2386.8

$L = 1.5 m = 1500 m m$
AL = OL = 20 mm
$L_{t o t a l} = 20 + 1500 + 20 = 1540 m m$
W = 5.5 + 600 + 5.5 = 611 mm

Number of required stroke $= \frac{W}{f} = \frac{611 m m}{2 m m / s t r o k e} = 305.5 ≃ 306$

Planning time $= \frac{W}{f} [\frac{L_{t o t a l}}{V_{f o r w a r d}} + \frac{L_{t o t a l}}{V_{r e t u r n}} + T_{r e v e r s i n g t a b l e}]$

$= 306 [\frac{1540}{21 \times 1000} + \frac{1540}{42 \times 1000} + 0.02]$

$= 39.78 m i n ≃ 2386.8 s e c$

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