1. The tool life is said to be over if
a) poor surface finish is obtained
b) there is sudden increase in cutting forces and power consumption
c) overheating and fuming due to heat of friction starts
d) all of the mentioned
Explanation: all of the mentioned
2. Tool life is generally better when
a) grain size of the metal is large
b) grain size of the metal is small
c) hard constituents are present in the micro structure of the tool material
d) none of the mentioned
Explanation: Tool life is generally better when grain size of the metal is large
3. The relation between the tool life(T) in minutes and cutting speed (V) in m/min is
a) VnT = C
b) VTn = C
c) Vn/T = C
d) V/Tn = C
Explanation: VTn = C
4. Using the Taylor Equation for tool life and letting n = 0.5 and C = 120, calculate the percentage increase in tool life when the cutting speed is reduced by 50%.
a) 100%
b) 200%
c) 300%
d) 400%
Explanation: Since n = 0.5, the Taylor equation can be rewritten as VT0.5 = 120.
Let’s denote V1 as the initial speed and V2 the reduced speed; thus, V2 = 0.5 V1. Because C is the constant 120, we have the relationship
0.5V1 sqrt T2 = V1sqrt T1
Simplifying this equation, T2/T1 = 1/0.25 = 4. This
indicates that the change in tool life is
(T2 – T1/ T1) = (T2/T1) – 1 = 4 – 1 = 3,
or that tool life is increased by 300%. Thus, a reduction in cutting speed has resulted in a major increase in tool life. Note also that, for this problem, the magnitude of C is not relevant
5. The various cutting tool materials used are:
a) high speed steels
b) cast cobalt alloys
c) carbides
d) all of the mentioned
Explanation: Materials used for cutting tools are
a) high speed steels
b) cast cobalt alloys
c) carbides
d) coated tools
e) alumina-based ceramics
f) cubic boron nitride
g) silicon nitride based ceramics
h) diamond
i) whisker reinforced materials and nano materials
6. High speed steels are suitable for making
a) high positive rake angle tools
b) interrupted cuts
c) machine tools with ow stiffness that are subject to vibration
d) all of the mentioned
Explanation: Because of their toughness (hence high resistance to fracture), high-speed steels are suitable especially for (a) high positive rake-angle tools (i.e., those with small included angles), (b) interrupted cuts, (c) machine tools with low stiffness that are subject to vibration and chatter, and (d) complex and single-piece tools, such as drills, reamers, taps, and gear cutters.
7. ___________ improves toughness, wear resistance, and high temperature strength.
a) Chromium
b) vanadium
c) Tungsten
d) None of the mentioned
Explanation: Chromium improves toughness, wear resistance, and high-temperature strength. Vanadium improves toughness, abrasion resistance, and hot hardness.
Tungsten and cobalt have similar effects, namely, improved strength and hot hardness.
Molybdenum improves wear resistance, toughness, and high-temperature strength and hardness.
8. _____________ contains nickel molybdenum matrix.
a) Chromium
b) Titanium carbide
c) Tungsten
d) None of the mentioned
Explanation: Titanium carbide (TiC) consists of a nickel-molybdenum matrix. It has higher Wear resistance than tungsten carbide but is not as tough. Titanium carbide is suitable for machining hard materials (mainly steels and cast irons) and for cutting at speeds higher than those appropriate for tungsten carbide
9. Coating materials used are
a) titaniun nitride
b) titanium carbide
c) titanium carbonitride
d) all of the mentioned
Explanation: Commonly used coating materials are titanium nitride (TiN), titanium carbide (TiC), titanium carbonitride (TiCN), and aluminum oxide (Al2O3).
10. Characteristics of coated cutting tools are:
a) high hardness
b) chemical stability
c) low thermal conductivity
d) all of the mentioned
Explanation: Coatings for cutting tools and dies should have the following general characteristics:
-> High hardness at elevated temperatures, to resist wear.
-> Chemical stability and inertness to the workpiece material, to reduce wear.
-> Low thermal conductivity, to prevent temperature rise in the substrate.
-> Compatibility and good bonding to the substrate, to prevent flaking or spalling.
-> Little or no porosity in the coating, to maintain its integrity and strength.