A NC drill press is to perform a series of through-hole drilling operations on a 1.75 in thick aluminum plate that is a component in a heat exchanger. Each hole is ¾ in diameter. There are 100 holes in all, arranged in a 10 by 10 matrix pattern, and the distance between adjacent hole centers (along the square) = 1.5 in. The cutting speed = 300 ft/min, the penetration feed (z-direction) = 0.015 in/rev, and the feed rate between holes (x-y plane) = 15.0 in/min.
Assume that x-y moves are made at a distance of 0.5 in above the work surface and that this distance must be included in the penetration feed rate for each hole. Also, the rate at which the drill is retracted from each hole is twice the penetration feed rate. The drill has a point angle = 100 degrees.
Determine 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.

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

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explanation: