Question

Question 5 Which one of the following is a wrong reason to coat the cutting tools? O To increase hot hardness and impact resistance O None To Increase the resistance to wear and cracking To make the tools sharper O To have lower friction Question 6 Machinability index of a workplece decrease if: The surface finish and surface integrity of the machined part is better O Nice discontinuous chip is created O Tool life is longer, O More force and power is required O We cut aluminum instead of steel Question 7 Which of the following statement is wrong about the wear and dressing of grinding wheels? The pores of grinding wheels are cleaned with flame to dress them O The grinding wheels are dressed by removing materlal from their surface with diamond tool The grains of the grinding wheel develop microcracks with wear Workplece materlal fill the pores of the grinding wheel with wear O None all correct Question 8 Which of the following statement is wrong about broaching? O None-all correct Parts may be made by surface broaching O Parts may be made by Internal broaching O The diameter of the roughening teeth is larger than the finishing teeth OApull type internal broach has roughening, semi finishing and finishing teeth

Answer 1

Q 5. Coatings are applied to cutting tools for following reasons: to reduce the friction between tool and the workpiece, to resist the cutting tool from getting oxidized, to improve wear resistance property of the cutting tool, to improve thermal resistance of the cutting tool, to improve the shock-absorbing property of the tool, to maintain the sharpness of the cutting too, etc.

The question is "Which of the following reason is wrong reason to coat the cutting tool?"

Let's discuss the options:

a. As coating can improve the thermal resistance and shock absorbing property, option "a" is wrong

b. We will see other options first

c. Coating can improve wear resistance property of the cutting tool, so "c" is wrong

d. Coating is used to maintain the sharpness of the cutting tool, it is not used to make the tool sharper. To make the tool sharper other machining processes, like grinding, are used. So, option "d" is the correct choice

e. Coating is used to reduce the friction between tool and workpiece, so "e" is also wrong.

Ans. d

Q 6. Machinability is the ease with which machining operations (shaping, planning, turning, drilling, milling, grinding) are performed on a given material. It is the ability of the material to get machined. Machinability is a relative term, therefore another term is defined, which is called Machinability Index. Machinability Index is used to find machinability of only one material. Machinability index= (V₆₀/V_60R), where V₆₀ is the cutting speed achieved by material for 60 min tool life and V_60R is the cutting speed achieved by a standard metal for 60 min tool life.

Under similar cutting conditions among the two materials(workpieces), machinability will be higher in:

1. Material which requires less cutting force and power

2. Material which produces high surface finish

3. Material which gives better tool life, and

4. Material which utilizes less specific machining energy.

Now, in question, it is asked"Machinability Index decreases if"

Looking at the options given in the questions,

a. As per above explanation, "a" option is wrong because high surface finish means high machinability.

b. Discontinuous chip may affect machinability. It is true that discontinuous chip occurs at low cutting speed and therefore machinability index may be low but tool life is also involved, so we cannot say. Option b is wrong.

c. Longer tool life means high machinability, so c is wrong

d. More force and power required means less machinability, so d is correct.

e. Machinability index of Aluminium (300-1500) is more than steel (25-65 approx.), so e is wrong

Answer: d