GATE Metallurgical Engineering Manufacturing Processes Syllabus

Manufacturing Processes syllabus — full chapter and topic list

Expand any chapter to see its topics and sub-topics. This is the whole examinable outline for Manufacturing Processes in GATE Metallurgical Engineering, not a summary of it.

1. 1

   Metal casting

   3 topics

   • Mould design involving feeding, gating and risering
   • Casting practices
   • Casting defects
2. 2

   Hot, warm and cold working of metals

   7 topics

   • Metal forming - fundamentals of metal forming processes
   • Rolling
   • Forging
   • Extrusion
   • Wire drawing
   • Sheet metal forming
   • Defects in forming
3. 3

   Metal joining

   6 topics

   • Principles of soldering
   • Principles of brazing
   • Principles of welding
   • Welding metallurgy
   • Defects in welded joints in steels
   • Defects in welded joints in aluminium alloys
4. 4

   Powder metallurgy

   3 topics

   • Production of powders
   • Compaction
   • Sintering
5. 5

   Non-destructive Testing (NDT)

   6 topics

   • Dye-penetrant
   • Ultrasonic
   • Radiography
   • Eddy current
   • Acoustic emission
   • Magnetic particle inspection methods

Manufacturing Processes flashcards for GATE Metallurgical Engineering

25 of 62 cards from the Manufacturing Processes deck — real questions with worked answers.

1. In casting, what is a riser (feeder) and what is its primary function?

   A riser is a reservoir of molten metal attached to the casting that feeds liquid metal to compensate for solidification (liquid-to-solid) shrinkage, preventing shrinkage cavities/porosity. To work, the riser must solidify after the casting section it feeds.

2. State Chvorinov's rule for solidification time of a casting and define its terms.

   $$t_{s} = B\left(\frac{V}{A}\right)^{n}$$ where $t_{s}$ is solidification time, $V$ is casting volume, $A$ is surface area, $B$ is the mould constant, and $n \approx 2$. The ratio $\frac{V}{A}$ is the modulus; larger modulus means slower solidification.

3. Using Chvorinov's rule, what is the design condition for a riser to be effective?

   The riser must solidify after the casting, so its modulus must exceed the casting's: $\frac{V_{riser}}{A_{riser}} > \frac{V_{casting}}{A_{casting}}$. A common design rule is $M_{riser} \geq 1.2\,M_{casting}$ (sphere/cylinder shapes maximize the modulus).

4. What is the purpose of a gating system in casting, and name its main elements?

   The gating system delivers molten metal smoothly into the mould cavity while minimizing turbulence, oxidation and erosion. Main elements: pouring basin, sprue, sprue well, runner, and ingate (gate). It also helps trap slag/dross and promote directional solidification.

5. Distinguish a pressurized from an unpressurized gating system by their gating ratio.

   Gating ratio = sprue area : runner area : ingate area. Pressurized: smallest area at the gate (e.g. $1:2:1$ or $1:0.75:0.5$), keeps system full and reduces aspiration but increases turbulence. Unpressurized: largest area at the gate (e.g. $1:2:2$ or $1:4:4$), reduces turbulence/velocity but the system may not run full.

6. Why is a sprue tapered (made wider at the top), and what governs the velocity at its base?

   The sprue is tapered to match the natural acceleration of the falling stream so the metal stays full and air aspiration is avoided. By Bernoulli/Torricelli, exit velocity at the sprue base is $v = \sqrt{2 g h}$, where $h$ is the effective head. Continuity ($A_1 v_1 = A_2 v_2$) requires the area to shrink as velocity increases.

7. State the relation used to size a tapered sprue so it remains full (areas vs heights).

   From continuity and $v = \sqrt{2gh}$: $\frac{A_{top}}{A_{base}} = \sqrt{\frac{h_{base}}{h_{top}}}$, i.e. $A \propto \frac{1}{\sqrt{h}}$. The cross-section must decrease downward in inverse proportion to the square root of the head.

8. What is directional solidification and how does Chvorinov's rule help achieve it?

   Directional solidification means freezing progresses from the thinnest/farthest sections toward the riser so feed metal is always available to the still-liquid zone, eliminating internal shrinkage. By controlling section moduli (and using chills, padding, and risers) the riser is made the last region to solidify.

9. Define total casting shrinkage and its three stages.

   Total shrinkage occurs in three stages: (1) liquid contraction as the melt cools to freezing point, (2) solidification (liquid-to-solid) contraction, fed by risers, and (3) solid (patternmaker's) contraction as the solid cools to room temperature, compensated by oversizing the pattern with shrinkage allowance.

10. What is shrinkage (patternmaker's) allowance and why is it added to the pattern?

    Shrinkage allowance is extra dimension added to the pattern to compensate for solid-state contraction of the casting as it cools from solidus to room temperature, so the final casting has correct dimensions. It is given per unit length and depends on the alloy (e.g. cast iron $\approx 10\,\text{mm/m}$, steel $\approx 20\,\text{mm/m}$).

11. List the common pattern allowances provided in casting.

    Shrinkage (contraction) allowance, machining (finish) allowance, draft (taper) allowance for easy withdrawal, distortion (camber) allowance, and shake (rapping) allowance which is negative to offset cavity enlargement from rapping.

12. Name the typical defects caused by gas in castings and a key cause of each.

    Blowholes/porosity: trapped gas from low mould permeability or excessive moisture; pinholes: dissolved gas (e.g. hydrogen) released on solidification; gas porosity: gas rejected during freezing. Remedies include degassing the melt, drying the mould, and improving venting/permeability.

13. What is a cold shut and a misrun in castings, and their common cause?

    A cold shut is a discontinuity/weak line where two metal streams meet but fail to fuse; a misrun is an incompletely filled cavity. Both arise from low pouring temperature, low fluidity, thin sections, or poor gating. Remedies: raise pouring temperature, improve fluidity and gating.

14. Define a hot tear (hot crack) casting defect and its cause.

    A hot tear is an irregular crack formed at high temperature while the casting is still weak, caused by contraction stresses being restrained by the mould/cores (poor collapsibility) during the last stages of solidification. Remedies: improve mould/core collapsibility, provide adequate fillets, and reduce restraint.

15. What are shrinkage cavities and how do they differ from gas porosity?

    Shrinkage cavities are voids from inadequate liquid feeding during solidification contraction (often angular/dendritic, located in hot spots). Gas porosity is from trapped/dissolved gas (rounded, smooth pores). Shrinkage is cured by proper risering/chills; gas porosity by degassing and venting.

16. What is the fundamental volume-constancy (incompressibility) condition in bulk metal forming?

    Plastic deformation conserves volume (negligible density change), so $A_0 L_0 = A_f L_f$ and in terms of strains $\varepsilon_1 + \varepsilon_2 + \varepsilon_3 = 0$ (using true strains). This underlies relations between true strain and area reduction.

17. Define true strain and engineering strain, and the relation between them.

    Engineering strain $e = \frac{L - L_0}{L_0}$; true strain $\varepsilon = \ln\!\frac{L}{L_0}$. They are related by $\varepsilon = \ln(1 + e)$. True strain is additive and used in forming analysis.

18. Write the power-law (Hollomon) flow stress equation and define its parameters.

    $$\sigma = K\,\varepsilon^{\,n}$$ where $\sigma$ is true flow stress, $\varepsilon$ is true plastic strain, $K$ is the strength coefficient, and $n$ is the strain-hardening exponent ($0 \leq n \leq 1$). Higher $n$ gives more uniform stretching before necking.

19. Define average (mean) flow stress and why it is used in forming work calculations.

    Average flow stress $\bar{\sigma} = \dfrac{K\,\varepsilon^{\,n}}{n+1}$, the mean of the flow-stress curve from $0$ to true strain $\varepsilon$. It is multiplied by the volume and total strain to estimate ideal deformation work/energy in bulk forming.

20. What is the Considère criterion for the onset of necking (diffuse instability) in tension?

    Necking begins when $\frac{d\sigma}{d\varepsilon} = \sigma$. For a material obeying $\sigma = K\varepsilon^{n}$, this gives the true strain at necking $\varepsilon_{u} = n$, i.e. uniform elongation equals the strain-hardening exponent.

21. Distinguish hot working from cold working in terms of recrystallization temperature.

    Hot working occurs above the recrystallization temperature: no strain hardening (dynamic recrystallization), large deformation possible, lower forces, poorer finish/tolerance, oxide scale. Cold working occurs below it: strain hardening, improved strength and finish, better tolerances, higher forces, residual stresses.

22. For flat rolling, give the formula for projected contact length and draft.

    Draft $d = h_0 - h_f$ (reduction in thickness). For roll radius $R$, the projected arc of contact length is $L = \sqrt{R\,d} = \sqrt{R(h_0 - h_f)}$ (small-angle approximation), where $h_0$ and $h_f$ are entry and exit thicknesses.

23. Define the angle of bite (acceptance angle) in rolling and the condition for the strip to be drawn in.

    The bite angle $\alpha$ is the contact angle at entry. For self-feeding without slipping, $\tan\alpha \leq \mu$ (i.e. $\mu \geq \tan\alpha$), where $\mu$ is the friction coefficient. The maximum draft is $d_{max} = \mu^{2} R$.

24. What is the neutral (no-slip) point in rolling?

    The neutral point is the location in the roll gap where the strip and roll surfaces move at the same velocity. Before it (entry side) the strip is slower than the roll (friction acts forward, drawing metal in); after it the strip is faster (friction acts backward). Roll-force pressure peaks at the neutral point ('friction hill').

25. Give the approximate roll force expression in flat rolling and define the terms.

    $$F = \bar{\sigma}\,L\,w$$ where $\bar{\sigma}$ is the average flow stress (plane-strain, $\approx 1.15\sigma_Y$), $L = \sqrt{R\,d}$ is the projected contact length, and $w$ is the strip width. Torque per roll $\approx F \cdot \frac{L}{2}$ and power $P = 2\pi N (FL/2)$ approximately.

See more Manufacturing Processes flashcards →

Planning Manufacturing Processes for GATE Metallurgical Engineering

Manufacturing Processes (GATE Metallurgical Engineering) FAQ