# Mechanical Engineer Interview Questions

## A CNC vertical milling machine has to cut a straight slot of 10 mm width and 2 mm depth by a cutter of 10 mm diameter between points (0,0) and (100,100) on the XY plane (dimensions in mm). The feed rate used for milling is 50 mm/min. Milling time for the slot (in seconds) is

(A) 120
(B) 170
(C) 180
(D) 240

(B) 170

Hint:

Given : width (b) = 10 mm, depth = 2 mm

Distance traveled for cut between points (0,0) and (100,100).
By Pythagoras theorem

## A solid cylinder of diameter 100 mm and height 50 mm is forged between two friction-less flat dies to a height of 25 mm. The percentage change in diameter is

(A) 0
(B) 2.07
(C) 20.7
(D) 41.4

(D) 41.4

Hint:

Since volume of cylinder remains same. Therefore,
Volume before forging = Volume after forging

Percentage change in diameter

## In a single pass drilling operation, a through hole of 15 mm diameter is to be drilled in a steel plate of 50 mm thickness. Drill spindle speed is 500 rpm, feed is 0.2 mm/rev and drill point angle is 118°. Assuming 2 mm clearance at approach and exit, the total drill time (in seconds) is

(A) 35.1
(B) 32.4
(C) 31.2
(D) 30.1

(A) 35.1

Hint:

BC = radius of hole or drill bit (R)
= 15 /2
= 7.5 mm

From ABC,

Travel distance of drill bit
l = thickness of steel plate (t) + clearance at approach + clearance at exit + AB
= 50 mm+ 2 + 2 + 4.506

= 58.506 mm
Feed rate

## In a single pass rolling process using 410 mm diameter steel rollers, a strip of width 140 mm and thickness 8 mm undergoes 10% reduction of thickness. The angle of bite in radians is

(A) 0.006
(B) 0.031
(C) 0.062
(D) 0.600

(C) 0.062

Hint:

t1 = 8 mm, d = 410 mm, r = 205 mm
Reduction of thickness, Dt = 10% of t1

## The maximum possible draft in cold rolling of sheet increases with the

(A) increase in coefficient of friction
(B) decrease in coefficient of friction
(D) increase in roll velocity

(A) increase in coefficient of friction

Hint:

The main objective in rolling is to decrease the thickness of the metal.
The relation for the rolling is given by

Where,
F = tangential frictional force

𝜇 = Coefficient of friction

𝑃𝑟 = Normal force between the roll and work piece

Now, from the increase in 𝜇, the draft in cold rolling of sheet increases.

## The crystal structure of austenite is

(A) body centered cubic
(B) face centered cubic
(C) hexagonal closed packed
(D) body centered tetragonal

(B) face centered cubic

Hint:

Austenite is a solid solution of carbon in γ -iron. It has F.C.C structure. It has a solid solubility of up to 2% C at 1130°C.

(A) 22°
(B) 26°
(C) 56°
(D) 76°

(B) 26°

Hint:

## Machining process                         Mechanism of material removal P. Chemical machining                           1. Erosion Q. Electro-chemical machining              2. Corrosive reaction R. Electro-discharge machining             3. Ion displacement S. Ultrasonic machining                         4. Fusion and vaporization

(A) P-2, Q-3, R-4, S-1
(B) P-2, Q-4, R-3, S-1
(C) P-3, Q-2, R-4, S-1
(D) P-2, Q-3, R-1, S-4

(A) P-2, Q-3, R-4, S-1