Question

A through hole of diameter 20.0 mm is to be drilled through a steel plate that is 50 mm thick. Cutting conditions are: cutting speed - 25 m/min, feed- 0.08 mm/rev, and the point angle of the drill- 1180. If machining time begins as soon as the drill makes contact with the work, how much time will the drilling operation take? O a 1.57 sec Ob. 1.76 min Od 1.76 sec O d. 1.57 min A department employing 85 workers with a hourly rate of 205, produced 30 batches per year per worker and the average batch size is 900 parts. The department hired analysts to set new standards. Improvements were 25%. With the same number of workers, workload has increased; starting cost of each unit is 55 and selling price is 8$. Determine the annual increase in profits after introduction of the standards

Answer 1

Given data:Diameter of through hole = 20.0 mmThickness of plate = 50 mmCutting speed = 25 m/minFeed = 0.08 mm/revPoint angle of the drill = 1180The formula for drilling time is:Drilling time (t) = L/ f × nWhere L is the length of the hole to be drilledf is the feedn is the number of revolutions required for drilling the holeFind the length of the hole to be drilled:Since the hole is drilled through a 50 mm thick plate, the length of the hole to be drilled is 50 mm.Therefore, L = 50 mmNow, we need to find the number of revolutions required to drill the hole. The number of revolutions required for drilling can be calculated using the formula:n = (cutting speed)/(π × d)where d is the diameter of the drill bitSubstitute cutting speed = 25 m/min, diameter (d) = 20.0 mm = 0.02 m in the above equation:n = (25)/(π × 0.02) = 397.89 rev/min≈ 400 rev/minNow, we can calculate the drilling time:t = L/ f × nSubstitute L = 50 mm, f = 0.08 mm/rev, and n = 400 rev/min in the above equation:t = 50/ (0.08 × 400) sec = 1.57 secHence, the drilling operation takes 1.57 sec, option (a) is correct.