solved anna university problems on machining time

SOLVED ANNA UNIVERSITY PROBLEMS ON MACHINING TIME

AU Problem 2.2

A blank 180 mm long and 70 mm diameter is to be machined in a lathe to 175 mm long and 60 mm diameter. The workpiece rotates at 450 rpm, the feed is 0.3 mm/rev and the maximum depth of cut is 2 mm. For turning operation; the approach plus over-travel distance is 6 mm. Assuming that the facing operation is done after the turning. Calculate the machining time.

Similar to Problem 2.21 on Page 2.60.

[ Ans:- Turning‘time = 4.13 min; Facing time = 0.66 min and Total time, T = 4.79 min]

AU Problem 2.3

A hollow workpiece of 50 mm diameter and 200 mm long is to be turned over in 4 passes. If the approach length is 20 mm over travel 10 mm, feed 0.8 mm/rev and cutting speed 30 m/min. Find the machining time.

Similar to Problem 2.19 on Page 2.59.

[Ans:- T = 6 min.]

AU Problem 2.4

Calculate the change gears to cut a single start thread M16 of 2 mm pitch on a centre lathe, having a lead screw of 6 mm pitch. (A typical set contains the following change gears with number of teeth: 20, 25, 30, 35, 40, 45, 50, 55, 60, 65 and 70).

Solution:

The gear train consists of 20 teeth on the driver and 60 teeth on driven (lead screw gear) to be used without intermediate gear. Ans.

AU Problem 2.5

A high-strength cast-iron bar 200 mm in diameter is being turned on a lathe at a depth of cut d = 1.25 mm. The specific power required to machine cast iron is 3.3 W.s/mm3. The lathe is equipped with a 12 kW electric motor and has a mechanical efficiency of 80%. The spindle speed is 500 rpm. Estimate the maximum feed that can be used before the lathe begins to stall.

Given data:

D = 200 mm

d = 1.25 mm

Specific power, Ps = 3.3 W.s/mm3

P = 12 kW = 12000 W

η = 80%

N = 500 rpm

Solution:

Actual power consumption of motor = P/η = 12/0.8 = 15 kW

AU Problem 2.6

A 150 mm long, 12.5 mm diameter 304 stainless steel rod is being reduced in diameter to 12.0 mm by turning on a lathe. The spindle rotates at N = 400 rpm, and the tool is travelling at an axial speed of 200 mm/min. Calculate the cutting speed, material removal rate, cutting time, power dissipated and cutting force.

Given data:

L = 150 mm

D1 = 12.5 mm

D2 = 12.0 mm

N = 400 rpm

Va = 200 mm/min

Solution:

Specific power for stainless ranges from 2-5 Ws/mm3. It is assumed as 4Ws/mm3.

We know that

Power consumption,

P = Specific power × MRR = 4 × 1924.23/60 = 128.28 W