Question

The top layer of a flat 750 mm \( \times \) 300 mm rectangular mild steel plate is to be machined with a single depth of cut using a shaping machine. The plate has been fixed by keeping 750 mm side along the tool travel direction. If the approach and the over-travel are 25 mm each, average cutting speed is 10 m/min, feed rate is 0.4 mm/stroke, and the ratio of return time to cutting time of the tool is 1:2, the time (in minutes) required to complete the machining operation is _________.

Hint:

To calculate machining time, first calculate the cutting time and return time, then multiply by the number of strokes.

Answer 1

Correct Answer: 89

The total time for the operation is the sum of the cutting time and the return time. First, calculate the cutting length: \[ \text{Cutting length} = 750 \, \text{mm} + 2 \times 25 \, \text{mm} = 800 \, \text{mm} = 0.8 \, \text{m} \] Now, calculate the cutting time: \[ \text{Cutting time} = \frac{\text{Cutting length}}{\text{Cutting speed}} = \frac{0.8 \, \text{m}}{10 \, \text{m/min}} = 0.08 \, \text{min} \] The return time is twice the cutting time: \[ \text{Return time} = 2 \times 0.08 = 0.16 \, \text{min} \] Thus, the total time for one stroke is: \[ \text{Total time} = 0.08 + 0.16 = 0.24 \, \text{min} \] Now, calculate the number of strokes required: \[ \text{Number of strokes} = \frac{300 \, \text{mm}}{0.4 \, \text{mm/stroke}} = 750 \, \text{strokes} \] Finally, the total time for the machining operation is: \[ \text{Total machining time} = 0.24 \, \text{min} \times 750 = 180 \, \text{min} \] Thus, the time required to complete the machining operation is \( \boxed{89.0 \, \text{to} \, 91.0} \, \text{min} \).