Answer:
The answer to the question is;
The time required from the beginning of the first hole to the completion of the last hole, assuming the most efficient drilling sequence will be used to accomplish the job is
26.785 min
Explanation:
The given parameters are
Thickness of plate = 1.75 in
Diameter of each plate = 3/4 in
Number of holes = 100
Holes arrangement = 10×10 square
Distance between adjacent holes = 1.5 in
Cutting speed = 300 ft/min
Penetration feed = 0.015 in/rev
Transverse rate between holes x-y plane = 15 in/rev
Height of movement above work surface = 0.5 in
Retraction speed = 2×penetration speed
Tip angle = 100 °
We therefore have
Cutting speed = pi×D×n
Where
D = Diameter of drill = 3/4 in
n = Rate of revolution of drill
Therefore
300 ft/min = pi×3/4×n
n = 300/(pi×3/4) = 127.32 ft/min
= 1527.8875 in/min
Penetration rate = 0.015 in/rev
Therefore Penetration rate = 0.015 in/rev × 1527.8875 in/min = 22.92 in/rev
Tip angle = 100 °
Height of tip = 0.375/(tan(50)) = 0.31466 in
Total vertical motion of drill =
Plate thickness + Distance of movement above work surface + Height of drill tip
= 1.75 in + 0.5 in + 0.31466 in
= 2.564 in
Speed of penetration motion = (Distance of motion)/time
Time = Distance/Speed
= (2.564 in)/(22.918 in)
= 0.1119 min
Time of retraction = 0.5 × (Time of penetrative motion)
= 0.5 × 0.1119 = 0.05595 min
Total time to move in and out of each hole = 0.05595 min + 0.1119 min = 0.16785 min
Total time to drill 100 holes = 0.16785 × 100 = 16.785 min
Time for transverse motion = 15 in/min
Distance between each hole = 1.5 in
Time for motion between holes = 1.5/15 =0.1 min
Total time for 100 holes = 0.1×100 = 10 mins
Total time for completing the drilling
= 10 + 16.785 = 26.785 min
= 1527.7 rev/min