Manufacturing Processes Ii Practice Questions

Let's break down these processes to understand which one doesn't produce powders.

Atomization is a method where molten metal is sprayed using high-velocity gas or liquid jets, or centrifugal force, to create fine metal droplets that solidify into powder.
Ball milling involves grinding materials in a rotating drum with grinding media (balls), which break down larger particles into finer powder through impact and attrition.
Electrolysis can produce metal powders by depositing metal ions from an electrolyte onto a cathode, which are then collected and processed into powder.

Sintering, on the other hand, is a heat treatment process that takes existing powder particles and bonds them together into a solid, denser object. It involves heating a compacted powder form to a high temperature, below its melting point, allowing atomic diffusion to fuse the particles. Therefore, sintering is a consolidation process for powders, not a production process.

Here's how to approach this problem:

Concept: The energy released per second by an electron beam is essentially its electrical power. This is given by the fundamental formula $E = VI$, where $V$ is the accelerating voltage and $I$ is the beam current. Notice that other information provided, like the number of electrons per second for 1 Ampere and the conversion of eV to Joules, is extra and not needed for this specific calculation. It's often included in competitive exams to test your understanding of which concepts are relevant.

Calculation:
We are given:

• Voltage ($V$) = $150 \text{ kV} = 150 \times 10^3 \text{ V}$
• Current ($I$) = $15 \text{ mA} = 15 \times 10^{-3} \text{ A}$

Now, we can directly calculate the energy released per second:
$E = V \times I$
$E = (150 \times 10^3 \text{ V}) \times (15 \times 10^{-3} \text{ A})$
$E = 2250 \text{ J/s}$

CNC programming uses G-codes (for machine motion) and M-codes (for miscellaneous functions). To match the given codes with their functions:

• P (G01): This is a preparatory code for linear interpolation ($4$), meaning the tool moves in a straight line.
• Q (G03): This is a preparatory code for circular interpolation, counter-clockwise ($1$), guiding the tool along a counter-clockwise arc.
• R (M06): This is a miscellaneous code for a tool change ($3$), initiating the automatic tool replacement sequence.
• S (M02): This is a miscellaneous code signifying the end of program ($2$), stopping all machine operations.

Thus, the correct combination is P - 4, Q - 1, R - 3, S - 2.

The Merchant Circle helps us relate the forces in a metal cutting operation. From the provided Merchant Circle diagram, we identify the friction force as $F = f_6$ and the normal force as $N = f_5$. The coefficient of friction $\mu$ is defined as the ratio of the friction force to the normal force, which is also equal to the tangent of the friction angle $\beta$. Therefore, the coefficient of friction is given by $\mu = \tan \beta = \frac{F}{N} = \frac{f_6}{f_5}$.

In the Carbon Dioxide (\text{CO}_2$) moulding process, also known as the gassing process, a mixture of sand and binder is hardened by passing$\text{CO}_2$gas. The$\text{CO}_2$reacts with the binder, causing it to solidify and bind the sand grains. The primary binder used for this chemical reaction is Sodium silicate (water glass). When$\text{CO}_2$is introduced, it lowers the$\text{pH}$of the sodium silicate-sand mixture, leading to the precipitation of silica gel, which coats the sand grains and provides strength to the mould. While bentonite clays are used \in green sand moulding and phenol formaldehyde resins \in other processes, they are not activated by$\text{CO}_2$ in this specific moulding technique.

In chemical machining, we use chemicals (etchants) to remove material. Imagine you apply a protective "mask" on your workpiece and then dip it into the etchant. Ideally, material should only be removed downwards, creating a "depth of cut" (vertical removal). However, the etchant also attacks sideways under the mask, which we call "undercut" (horizontal removal).

The Etch Factor is a critical parameter that tells us how much sideways etching (undercut) happens compared to the downward etching (depth of cut). It's defined as the ratio of the Undercut to the Depth of Cut.

Mathematically, the etch factor ($F_e$) is expressed as:
$\text{Etch Factor} (F_e) = \frac{\text{Undercut}}{\text{Depth of Cut}}$
This ratio helps us predict the final shape of the etched feature.

Comparing this definition with the given options:

• A. Depth of cut/ Undercut: This is the inverse of the etch factor.
• B. Tool wear/ Workpiece wear: This concept is relevant to mechanical processes, not chemical machining geometry.
• C. Undercut/depth of cut: This perfectly matches our definition of the etch factor.
• D. Workpiece wear/tool wear: Similar to option B, this relates to mechanical wear.

Therefore, the etch factor is correctly expressed as the ratio of undercut to depth of cut.

Machining operations shape a workpiece by removing material. A single-point cutting tool has only one primary cutting edge. Turning uses a single-point tool as the workpiece rotates against it, and the tool moves linearly to reduce diameter or create features. Boring enlarges existing holes, typically using a boring bar that holds a single-point tool, similar to internal turning. In contrast, drilling uses drill bits with multiple cutting edges (multi-point tools), and milling employs rotating cutters with multiple teeth (multi-point tools). Therefore, both turning and boring are commonly performed using single-point cutting tools.

This problem asks us to find the angle of the deformation zone during a rolling process. We're given the initial thickness of the metal strip, the roll diameter, and the desired reduction in cross-sectional area.

First, let's determine the reduction in thickness. Since the width remains constant, a 10% reduction in cross-sectional area means a 10% reduction in thickness.
Initial thickness, $t_0 = 12$ mm.
Reduction in thickness, $\Delta t = 0.10 \times 12 \text{ mm} = 1.2 \text{ mm}$.
The final thickness will be $t_f = t_0 - \Delta t = 12 \text{ mm} - 1.2 \text{ mm} = 10.8 \text{ mm}$.

Next, we calculate the roll radius and the length of the contact arc.
Roll diameter, $D = 800$ mm, so radius $R = D/2 = 400$ mm.
The length of the arc of contact, $L$, is approximated by the formula:
$L \approx \sqrt{R \times \Delta t}$
Substituting the values:
$L \approx \sqrt{400 \text{ mm} \times 1.2 \text{ mm}} = \sqrt{480} \text{ mm} \approx 21.909 \text{ mm}$
Finally, we calculate the angle subtended by this arc at the center of the roll, $\theta$. This angle is initially in radians and then converted to degrees.
$\theta_{\text{radians}} = \frac{L}{R} \approx \frac{21.909 \text{ mm}}{400 \text{ mm}} \approx 0.05477 \text{ radians}$
To convert to degrees:
$\theta_{\text{degrees}} = \theta_{\text{radians}} \times \frac{180^\circ}{\pi} \approx 0.05477 \times \frac{180^\circ}{\pi} \approx 3.138^\circ$
Rounding to two decimal places, the angle is $3.14^\circ$.

In Gas Tungsten Arc Welding (GTAW), pure tungsten electrodes have limitations in current carrying capacity. To enhance performance, especially electron emission (thermionic emission) which aids arc initiation, stability, and current capacity, specific oxides are added. Thorium oxide (ThO₂), typically $1\%$ to $2\%$ by weight, is added to tungsten to create thoriated tungsten electrodes. This addition significantly improves electron emission, allowing the electrode to handle higher currents without overheating or excessive degradation, making arc initiation easier and the arc more stable. Therefore, Thorium is the correct material used for this purpose.

In powder metallurgy, atomization is a crucial initial step that involves transforming molten metals into fine powder particles. This process works by disintegrating a stream of molten metal using high-energy fluids (like gas or water jets), causing it to solidify rapidly into powder. Therefore, atomization is explicitly a method for producing powders. Other options like compaction, sintering, and blending are subsequent steps in powder metallurgy that occur after the powders have been produced.

Let's break down how to find the length of approach ($l_a$) in peripheral milling. We can use a right-angled triangle formed by the cutter's center, the point where the cut begins, and a point on the cutter's circumference.

From the right-angled triangle $OA'B$ (referring to a standard diagram for slab milling where $OB$ is the cutter radius, $OA'$ is the distance from the center to the uncut surface, and $A'B$ is the length of approach):
We have the Pythagorean theorem: $(OB)^2 = (OA')^2 + (A'B)^2$.
Substituting the values:
$(\frac{D}{2})^2 = (\frac{D}{2} - d)^2 + A^2$

Now, let's simplify this equation:
$\frac{D^2}{4} = \frac{D^2}{4} + d^2 - 2 \frac{D}{2} d + A^2$
$\frac{D^2}{4} = \frac{D^2}{4} + d^2 - Dd + A^2$

Rearranging to solve for $A^2$:
$A^2 = Dd - d^2$
$A^2 = d(D - d)$

Taking the square root to find $A$:
$A = \sqrt{d(D - d)}$ ... (1)

In this specific question, we are given that $A = l_a$ (length of approach), $d = t$ (depth of cut), and $D = d$ (diameter of the milling cutter). Substituting these into equation (1):
$l_a = \sqrt{t(d - t)}$

To avoid the aspiration effect in the sprue, the ratio of the areas at the top and bottom of the sprue must satisfy the relation $\frac{{{{\bf{A}}_1}}}{{{{\bf{A}}_2}}} = \frac{{{{\bf{V}}_2}\;}}{{{{\bf{V}}_1}}} = {\bf{R}} = \sqrt {\frac{{{{\bf{h}}_{\bf{t}}} - {{\bf{h}}_s}}}{{{{\bf{h}}_{\bf{t}}}}}}$, where $h_t$ is the total height ($h_s + h_b$), $h_s$ is the sprue height, and $h_b$ is the pouring basin height. Given $h_s = 1500 \text{ mm}$ and $h_b = 100 \text{ mm}$, the total height is $h_t = 1500 + 100 = 1600 \text{ mm}$.

For circular cross-sections, $\frac{{{{\bf{A}}_1}}}{{{{\bf{A}}_2}}} = {\left( {\frac{{{{\bf{d}}_1}}}{{{d_2}}}} \right)^2}$. Substituting the values into the formula:
${\left( {\frac{{{{\bf{d}}_1}}}{{{d_2}}}} \right)^2} = \sqrt {\frac{{1600 - 1500}}{{1600}}} = \sqrt {\frac{{100}}{{1600}}} = \frac{{10}}{{40}}$
Therefore, $d_1 : d_2 = 1 : 2$.

The core concept here is calculating the feed rate in an Electrochemical Machining (ECM) process. We relate the Material Removal Rate (MRR) to the electrical parameters and then to the feed rate.

The formula for Material Removal Rate (MRR) by mass is given by:
$MRR = \frac{A \cdot I}{\rho \cdot Z \cdot F}$
Where:
$A$ = Atomic weight
$I$ = Input current
$\rho$ = Density of Iron
$Z$ = Valency
$F$ = Faraday's Constant

The MRR can also be expressed in terms of volume removed per unit time, which is the product of the machined surface area ($A_c$) and the feed rate ($f$):
$MRR = A_c \times f$
Equating these two expressions for MRR, we can find the feed rate ($f$):
$f = \frac{MRR}{A_c} = \frac{A \cdot I}{\rho \cdot Z \cdot F \cdot A_c}$

Given values:
$A = 55.85$
$I = 1000 \text{ A}$
$F = 96540 \text{ Coulombs}$
$\rho = 7860 \text{ kg/m}^3$ (which is $7860 \times 10^{-6} \text{ kg/mm}^3$ for consistency in units)
$Z = 2$
$A_c = 30 \text{ mm} \times 30 \text{ mm} = 900 \text{ mm}^2$

Substituting these values into the feed rate formula:
$f = \frac{55.85 \times 1000}{7860 \times 10^{-6} \times 2 \times 96540 \times 30 \times 30}$
$f = 0.04089 \text{ mm/sec}$
To convert this to mm/min, multiply by 60:
$f = 0.04089 \times 60 = 2.453 \text{ mm/min}$

Surface texture defines the quality of a machined surface, communicated through standard symbols. Key terms include:

• Flaws: Random imperfections like scratches or holes.
• Lay: The visible direction of the surface pattern from machining.
• Roughness: Fine, irregular surface deviations.
  • Roughness height ($R_a$): Deviation from the centerline.
  • Roughness width: Distance between successive roughness peaks.
• Waviness: Broader, recurrent deviations from a flat surface.
  • Waviness width: Distance between adjacent wave crests.
  • Waviness height: Height between the crests and valleys of the waves.

The standard symbol for surface texture provides specific locations for these parameters:

• Maximum roughness width rating: To the right of the lay symbol.
• Roughness width cut-off.
• Minimum value roughness height.
• Maximum value of roughness height.
• Maximum waviness height and Maximum waviness width value.

From the provided figure (assuming a standard representation where waviness height is typically placed above waviness width):
The waviness height is $50 \text{ } \mu \text{m}$.

Let's break down the key terms for precision in an NC machine's positioning system as shown in the figure.

Control Resolution ($n$): This refers to the smallest possible increment the NC machine can move its axis. Think of it as the smallest step size the system can physically make, determined by its digital-to-analog converter.

Repeatability ($m$): This describes how consistently the machine can return to a previously taught position. It's about precision in re-positioning. In the figure, it's represented by the statistical distribution of errors, specifically $\pm 3\sigma$ from the mean, where $\sigma$ is the standard deviation of the error. This range covers nearly all repeated attempts to reach the same point.

Accuracy ($l$): This measures how close the machine can get to a desired target point. It's the overall ability to hit the intended mark. The figure illustrates accuracy as the difference between the desired position and the mean of the actual positions achieved.

Based on these definitions and the representation in the figure, we can identify:

• $l$ represents Accuracy.
• $m$ represents Repeatability (the spread $\pm 3\sigma$ around the mean).
• $n$ represents Control resolution (the smallest discrete step).

The tool life $T$ in a turning operation is given by the relationship: $T = C v^{-2.5} f^{-0.9} d^{-0.15}$, where $C$ is a constant, $v$ is cutting speed, $f$ is feed, and $d$ is depth of cut.

Initially, with $v = 1.5$ m/s, $f = 0.25$ mm, and $d = 3$ mm, the initial tool life $T_1$ is:
$T_1 = C \times (1.5)^{-2.5} \times (0.25)^{-0.9} \times (3)^{-0.15} = 1.07166 C$
When the cutting speed is doubled to $v_2 = 3$ m/s, while other parameters remain unchanged ($f = 0.25$ mm, $d = 3$ mm), the new tool life $T_2$ is:
$T_2 = C \times (3)^{-2.5} \times (0.25)^{-0.9} \times (3)^{-0.15} = 0.18944 C$
The percentage change in tool life is calculated as:
$\text{Percentage change} = \frac{T_1 - T_2}{T_1} \times 100$
$\text{Percentage change} = \frac{1.07166 C - 0.18944 C}{1.07166 C} \times 100 = 82.32 \%$

The force required for punching depends on the shear strength of the material and the shear area. For a square hole, the shear area is given by $4Lt$, where $L$ is the side length and $t$ is the thickness.

Given $L_1 = 30~\text{mm}$, $t_1 = 1~\text{mm}$ for the first case, and $L_2 = 60~\text{mm}$, $t_2 = 2~\text{mm}$ for the second case.
The ratio of the forces is:
$\frac{F_1}{F_2} = \frac{4L_1t_1 \times \text{shear strength}}{4L_2t_2 \times \text{shear strength}} = \frac{L_1t_1}{L_2t_2} = \frac{30 \times 1}{60 \times 2} = 0.25$

The surface roughness parameter $R_a$ is defined as the arithmetic average of the absolute values of the roughness profile ordinates. The formula for $R_a$ is given by $R_a = \frac{\sum A}{n}$, where $A$ represents the product of the number of peaks and the height of the irregularities, and $n$ is the total number of irregularities.
From the given profile, we have the total number of irregularities $n = 17 \times 2$. The height of each irregularity is given as $2\ \mu m$. Applying the formula:
$R_a = \frac{17 \times (2 + 2)}{17 \times 2} = 2\ \mu m$