# Machining and Machine Tool Operation

 Question 1
In a pure orthogonal turning by a zero rake angle single point carbide cutting tool, the shear force has been computed to be 400 N. The cutting velocity, $V_c=100 \; m/min$, depth of cut, $t=2.2 \; mm$, feed, $s_0=0.1 \; mm/revolution$ and chip velocity, $V_f=20 \; m/min$, the shear strength, $\tau _s$ of the material will be _______MPa (round off to two decimal places).
 A 458.25 B 392.23 C 254.36 D 214.36
GATE ME 2021 SET-2   Manufacturing Engineering
Question 1 Explanation:
\begin{aligned} \alpha &=0^{\circ} \\ F_{s} &=400 \mathrm{~N} \\ \text { Cutting velocity }(\mathrm{V}) &=100 \mathrm{~m} / \min \left(V_{c}\right) \\ d &=2.0 \mathrm{~mm}(t) \\ f &=0.1 \mathrm{~mm} / \mathrm{rev}\left(S_{o}\right) \\ \text { Chip velocity }\left(V_{c}\right) &=20 \mathrm{~m} / \min \quad\left(V_{f}\right) \\ r &=\frac{t}{t_{c}}=\frac{l_{c}}{l}=\frac{V_{c}}{V} \quad\left(V_{c}=\text { chip velocity; } V=\right.\text { cutting velocity) }\\ &=\frac{20}{100}=0.2\\ \tan \phi &=\frac{r \cos \alpha}{1-r \sin \alpha}=\frac{0.2 \cos 0^{\circ}}{1-0.2 \sin 0^{\circ}}=0.2 \\ \phi &=11.31^{\circ} \\ & \frac{F_{S}}{A_{S}}=\frac{F_{S}}{\left(\frac{b t}{\sin \phi}\right)}=\frac{F_{S} \sin \phi}{f d} \\ t &=f \sin 90^{\circ} \\ b &=d \sin 90^{\circ} \\ b t &=f d \\ &=\frac{400 \sin 11.31^{\circ}}{0.1 \times 2.0} \mathrm{~N} / \mathrm{mm}^{2} \\ &=392.23 \mathrm{MPa} \end{aligned}
 Question 2
A surface grinding operation has been performed on a Cast Iron plate having dimensions 300 mm (length) x 10 mm (width) x 50 mm (height). The grinding was performed using an alumina wheel having a wheel diameter of 150 mm and wheel width of 12 mm. The grinding velocity used is 40 m/s, table speed is 5 m/min, depth of cut per pass is 50 $\mu m$ and the number of grinding passes is 20. The average tangential and average normal force for each pass is found to be 40 N and 60 N respectively. The value of the specific grinding energy under the aforesaid grinding conditions is __________$J/mm^3$ (round off to one decimal place).
 A 24.8 B 32.6 C 38.4 D 48.2
GATE ME 2021 SET-2   Manufacturing Engineering
Question 2 Explanation:
\begin{aligned} \text { Power } &=F_{c} \cdot V \\ &=40 \mathrm{~N} \times 40 \mathrm{~m} / \mathrm{s}=1600 \mathrm{~W} \\ \mathrm{MRR} &=10 \times 0.050 \times \frac{5000}{60} \mathrm{~mm}^{3} / \mathrm{s} \\ &=41.667 \mathrm{~mm}^{3} / \mathrm{s} \end{aligned} $e=\frac{\text { Power }}{\text { MRR }}=\frac{1600 \mathrm{~J} / \mathrm{s}}{41.667 \mathrm{~mm}^{3} / \mathrm{s}}=38.40 \mathrm{~J} / \mathrm{mm}^{3}$
 Question 3
The machining process that involves ablation is
 A Abrasive Jet Machining B Chemical Machining C Electrochemical Machining D Laser Beam Machining
GATE ME 2021 SET-2   Manufacturing Engineering
Question 3 Explanation:
Laser beam machining (LBM) is a nonconventional machining process, which broadly refers to the process of material removal, accomplished through the interactions between the laser and target materials. The processes can include laser drilling, cutting, grooving, writing, scribing, ablation, welding, cladding, milling, and so on. LBM is a thermal process, and unlike conventional mechanical processes, LBM removes material without mechanical engagement. In general, the workpiece is heated to melting or boiling point and removed by melt ejection, vaporization, or ablation.
 Question 4
In a grinding operation of a metal, specific energy consumption is 15 $J/mm^3$. If a grinding wheel with a diameter of 200 mm is rotating at 3000 rpm to obtain a material removal rate of 6000 $mm^3/min$, then the tangential force on the wheel is _______N (round off to two decimal places).
 A 42.25 B 62.45 C 47.75 D 28.24
GATE ME 2021 SET-1   Manufacturing Engineering
Question 4 Explanation:
\begin{aligned} E_{s p} &=15 \mathrm{~J} / \mathrm{mm}^{3} \\ \mathrm{MRR} &=6000 \mathrm{~mm}^{3} / \mathrm{min} \\ N &=3000 \mathrm{rpm} \\ D &=200 \mathrm{~mm} \\ E_{s p} &=\frac{F_{C} \mathrm{~V}}{L d V} \\ 15 &=\frac{F \times \frac{m}{m i n}}{600 \frac{m m^{3}}{\min }} \\ V &=\frac{\pi D N}{1 m}=\frac{\pi(200)(3 m)}{1000}=600 \times 3.14\\ 15 &=\frac{F \times 600 \times 3 \pi y}{6000} \\ F &=\frac{150}{\pi}=47.746 \mathrm{~N} \simeq 47.75 \mathrm{~N} \end{aligned}
 Question 5
An orthogonal cutting operation is performed using a single point cutting tool with a rake angle of $12^{\circ}$ on a lathe. During turning, the cutting force and the friction force are 1000 N and 600 N, respectively. If the chip thickness and the uncut chip thickness during turning are 1.5 mm and 0.75 mm, respectively, then the shear force is _______N (round off to two decimal places).
 A 247.65 B 685.77 C 457.36 D 825.66
GATE ME 2021 SET-1   Manufacturing Engineering
Question 5 Explanation:
$F_{c}=1000 \mathrm{~N}, F=600 \mathrm{~N}, t=0.75 \mathrm{~mm}, t_{c}=1.5 \mathrm{~mm}, \alpha=12^{\circ}$
This is orthogonal turning operation
\begin{aligned} r &=\frac{t}{t_{C}}=\frac{0.75}{1.5}=0.5 \\ \tan \phi &=\frac{0.5 \cos 12^{\circ}}{1-0.5 \sin 12^{\circ}} \\ \Rightarrow\quad \phi &=28.63^{\circ} \end{aligned}
Method - 1: Using force relations
\begin{aligned} F &=F_{c} \sin \alpha+F_{t} \cos \alpha \\ 600 &=1000 \sin 12^{\circ}+F_{t} \cos 12^{\circ}\\ \text{or}\qquad F_{t}&=400.85 \mathrm{~N} \\ \therefore \qquad F_{s}&=F_{c} \cos \phi-F_{t} \sin \phi\\ &=1000 \cos 28.63^{\circ}-400.85 \sin 28.63^{\circ} \\ &=685.66 \mathrm{~N} \end{aligned}
Method - 2 : Using Merchant circle
\begin{aligned} F_{c} &=R \cos (\beta-\alpha) \\ F &=R \sin \beta \\ \text{or}\quad \frac{F}{F_{c}} &=\frac{R \sin \beta}{R \cos (\beta-\alpha)} \end{aligned} \begin{aligned} \frac{600}{1000} &=\frac{\sin \beta}{\cos (\beta-12)} \\ 0.6 \cos \beta \cos 12^{\circ}+0.6 & \sin \beta \sin 12^{\circ}=\sin \beta \\ 0.586888 \cos \beta &=\left(1-0.6 \sin 12^{\circ}\right) \sin \beta=0.875253 \sin \beta \\ \tan \beta &=\frac{0.586888}{0.875253} \\ \Rightarrow \quad \quad \beta &=33.84^{\circ} \\ \therefore \quad F &=R \sin \beta \\ 600&=R \sin 33.84^{\circ}\\ \Rightarrow R&=1077.44 \mathrm{~N}\\ \therefore \quad F_{s}&=R \cos (\phi+\beta-\alpha)\\ &=1077.44 \cos \left(28.63^{\circ}+33.84^{\circ}-12^{\circ}\right)\\ &=685.77 \mathrm{~N} \end{aligned}
 Question 6
The correct sequence of machining operations to be performed to finish a large diameter through hole is
 A drilling, boring, reaming B boring, drilling, reaming C drilling, reaming, boring D boring, reaming, drilling
GATE ME 2021 SET-1   Manufacturing Engineering
Question 6 Explanation:
Drilling: to produce a hole, which then may be followed by boring it to improve its dimensional accuracy and surface finish.

Boring: to enlarge a hole or cylindrical cavity made by a previous process or to produce circular internal grooves.

Reaming: is an operation used to (a) make an existing hole dimensionally more accurate than can br achived by drilling alone and (b) improve its surface finish. The most accurate holes in workpieces generally are produced by the following sequence of operation.

Centering -> Drilling -> Boring -> Reaming.
 Question 7
In a machining operation, if a cutting tool traces the workpiece such that the directrix is perpendicular to the plane of the generatrix as shown in figure, the surface generated is A plane B cylindrical C spherical D a surface of revolution
GATE ME 2021 SET-1   Manufacturing Engineering
Question 7 Explanation: Question 8
Bars of 250 mm length and 25 mm diameter are to be turned on a lathe with a feed of 0.2 mm/rev. Each regrinding of the tool costs Rs. 20. The time required for each tool change is 1 min. Tool life equation is given as $VT^{ 0.2} = 24$ (where cutting speed V is in m/min and tool life T is in min). The optimum tool cost per piece for maximum production rate is Rs. ________ (round off to 2 decimal places).
 A 12.56 B 28.42 C 26.98 D 35.62
GATE ME 2020 SET-2   Manufacturing Engineering
Question 8 Explanation:
\begin{aligned} \text{Optimum tool life } \left(T_{o}\right)&=\frac{T_{c}(1-n)}{n} \\ &=\frac{1(1-0.2)}{0.2}=4 \mathrm{min} \\ V_{o} T_{o}^{n} &=C \\ \text { or } V_{o}&=\frac{C}{T_{o}^{n}}\\ &=\frac{24}{4^{0.2}}=18.19 \mathrm{m} / \mathrm{min} \\ V &=\pi D \mathrm{N} \\ \Rightarrow \quad 18.19 &=\pi \times 0.025 \times N \end{aligned}
$\Rightarrow N=231.6 \mathrm{rpm}$
Maching time per piece
$\left(T_{m}\right)=\frac{L}{f N}=\frac{250}{0.2 \times 231.6}=5.397 \mathrm{min}$
Number of tool needed per piece work
$=\frac{5.397}{4} \text { piece }$
$\therefore$ The optimum tool cost per piece
$=\frac{5.397}{4} \times 20=26.985$
 Question 9
A cylindrical bar with 200 mm diameter is being turned with a tool having geometry $0^{\circ}- 9^{\circ} - 7^{\circ} - 8^{\circ} - 15^{\circ} - 30^{\circ} - 0.05$ inch (Coordinate system, ASA) resulting in a cutting force $F_{c1}$. If the tool geometry is changed to $0^{\circ}- 9^{\circ} - 7^{\circ} - 8^{\circ} - 15^{\circ} - 0^{\circ} - 0.05$ inch (Coordinate system. ASA) and all other parameters remain unchanged, the cutting force changes to $F_{c2}$. Specific cutting energy (in $J/mm^3$) is $U_c = U_0 (t_1)^{-0.4}$, where $U_0$ is the specific energy coefficient, and $t_1$ is the uncut thickness in mm. The value of percentage change in cutting force $F_{c2}$, i.e. $\left ( \frac{F_{c2}-F_{c1}}{F_{c1}} \right ) \times 100$, is _______ (round off to one decimal place).
 A -2.5 B -5.59 C 5.59 D 2.5
GATE ME 2020 SET-2   Manufacturing Engineering
Question 9 Explanation:
\begin{aligned} C_{s 1}&=30^{\circ}\\ \therefore \quad \lambda_{1}&=90-30=60^{\circ} \\ C_{s 2}&=0^{\circ}\\ \therefore \lambda_{2}&=90-0=90^{\circ} \end{aligned}
We know that specific energy consumption
\begin{aligned} U_{C}&=\frac{F_{C}}{1000 \mathrm{fd}}=U_{0}\left(t_{1}\right)^{-0.4}(\text {given }) \\ \therefore \quad F_{C}&=U_{0}(f \sin \lambda)^{-0.4} \times 1000 \mathrm{fd}\\ \therefore \quad F_{c} &\propto(\sin \lambda)^{-0.4}\\ \therefore \quad &=\frac{F_{c 2}-F_{c 1}}{F_{c 1}} \times 100=\left[\left(\frac{\sin \lambda_{2}}{\sin \lambda_{1}}\right)^{-0.4}-1\right] \times 100 \\ &=\left[\left(\frac{\sin 90^{\circ}}{\sin 60^{\circ}}\right)^{-0.4}-1\right] \times 100=-5.59 \end{aligned}
 Question 10
The process, that uses a tapered horn to amplify and focus the mechanical energy for machining of glass, is
 A electrochemical machining B electrical discharge machining C ultrasonic machining D abrasive jet machining
GATE ME 2020 SET-2   Manufacturing Engineering
Question 10 Explanation:
In Ultrasonic machining, the function of horn (also called concentrator, it is a tapered metal bar) is to amplify and focus vibration of the transducer to an adequate intensity for driving the tool to fulfll the cutting operation.

There are 10 questions to complete. 