Question

A drilling operation is to be performed with a 12.7 mm diameter twist drill in a steel work part. The hole is a blind hole at a depth of 60mm and the point angle is 118°. The cutting speed is 25 m/min and the feed is 0.30 mm/rev. Determine (a) the cutting time to complete the drilling operation, and (b) metal removal rate during the operation, after the drill bit reaches full diameter.

Answer 1

Answer:

158.8 is the removal rate for this question

Answer 2

Given:

Diameter of twist drill = 12.7mm

Depth of hole = 60mm

Point angle = 118°

Cutting speed = 25m/min

Feed = 0.3mm/rev

To find:

Cutting time.

Metal Removal Rate

Solution:

The rotational speed of the drill is given by the formula:

$N=\frac{V}{\pi D}$

where $N,V,D$ are the rotational speed, cutting speed and the diameter of the drill respectively

Here, the cutting speed is in metres whereas the diameter is expressed in millimetres. Hence,

$V=25m/min$

$1m=1000mm$

$V=25*1000mm/min=25000mm/min$

$N=\frac{25000}{\pi *12.7}$

$N=\frac{25000}{3.142*12.7}= 626.5rev/min$

Next, we solve for the feed rate which is given by the formula,

$FR=N*F$

where $FR,N,F$ are the feed rate, rotational speed and feed of the drill respectively

$FR=0.30*626.5=187.95mm/min$

To determine the cutting time, we consider the formula as shown below:

$T_{m}=\frac{L}{FR}$

where, $T_{m}, L, FR$ are the cutting time, depth of hole drilled and feed rate of the drill.

$T_{m}=\frac{60}{187.95}=0.3192min$

Thus, the cutting time to complete the drilling operation is 0.3192 min.

The rate of metal removal is given by the formula:

$MRR=\frac{\pi D^{2} FR}{4}$

where, $MRR$ is the metal removal rate

$MRR=\frac{3.142*12.7^{2}*187.95}{4}$

$MRR=23812mm^{3} /min$

On converting to seconds,

$1 min=60s$

$MRR=\frac{23812}{60}=396.86mm^{3}/s$

Thus, the metal removal rate during the operation, after the drill bit reaches full diameter is 396.86mm³/s.

(a) The cutting time to complete the drilling operation is 0.3192 min.

(b) The metal removal rate during the operation, after the drill bit reaches full diameter is 396.86mm³/s.