Manufacturing Processes Syllabus

April 02, 2025

Manufacturing Processes

Complete Guide for GATE Metallurgy (MT) - Section 7 (TestUrSelf)

Table of Contents

1. Metal Casting
2. Metal Forming
3. Metal Joining
4. Powder Metallurgy
5. Non-Destructive Testing

7.1 Metal Casting

Mould Design

G

Gating System

R

Riser Design

F

Feeding

Key Principles

• Chvorinov's Rule: t_{solidification} ∝ (V/A)²
• Gating ratio: A_sprue:A_runner:A_gate (typically 1:2:2)
• Riser must solidify after casting (modulus > casting modulus)

Casting Defects

Defect	Causes	Prevention
Porosity	Gas entrapment, shrinkage	Proper venting, riser design
Misrun	Incomplete filling	Higher pouring temp, better fluidity
Hot tears	Restrained contraction	Better mold collapsibility

Casting Practices

Process	Tolerance (mm/mm)	Surface Finish (μm)	Applications
Sand Casting	±0.8-3.0	5-25	Large parts, low volume
Investment	±0.1-0.5	1.5-3.0	Complex shapes, high precision
Die Casting	±0.1-0.3	0.8-1.6	High volume, thin walls

7.2 Metal Forming

Hot, Warm & Cold Working

Process	Temperature	Advantages	Disadvantages
Hot Working	>0.6Tm	Low forces, no strain hardening	Oxidation, poor tolerances
Warm Working	0.3-0.5Tm	Reduced forces, better finish	Special equipment needed
Cold Working	<0.3Tm	Good finish, strain hardening	High forces, limited ductility

Metal Forming Processes

R

Rolling

F

Forging

E

Extrusion

D

Drawing

Key Formulas

Rolling: h_f = h₀ - 2R(1 - cosα) (α = bite angle)

Forging: F = Y_fA(1 + μD/3h) (Y_f = flow stress)

Extrusion: P = Y_fln(A₀/A_f) (ideal work)

Forming Defects

• Rolling: Edge cracks, alligatoring
• Forging: Laps, cold shuts
• Extrusion: Surface cracking, piping
• Drawing: Center burst, wrinkling

7.3 Metal Joining

Welding Processes

⚡

Arc Welding

🔥

Gas Welding

💥

Resistance

🔄

Friction

Welding Metallurgy

• Fusion zone: Rapid solidification structure
• HAZ: Grain growth, phase transformations
• Residual stresses due to thermal gradients

Example: Steel Welding

Preheat temperature calculation:

T_preheat (°C) = 144√CE - 392

Where CE = C + Mn/6 + (Cr+Mo+V)/5 + (Ni+Cu)/15

Joining Defects

Material	Common Defects	Prevention
Steels	Hydrogen cracks, porosity	Preheat, low-H electrodes
Al Alloys	Hot cracks, lack of fusion	Proper filler, high heat input

7.4 Powder Metallurgy

Powder Production

Method	Particle Size (μm)	Shape	Applications
Atomization	10-300	Spherical	High performance parts
Reduction	1-100	Irregular	Fe, W, Cu powders
Electrolysis	10-150	Dendritic	Cu, Fe powders

Compaction & Sintering

C

Compaction

S

Sintering

Key Parameters

Green density ≈ 80% theoretical (pressure dependent)

Sintering temperature ≈ 0.7-0.9T_m

Sintering Mechanisms

1. Initial: Neck formation
2. Intermediate: Pore rounding
3. Final: Pore elimination

7.5 Non-Destructive Testing

NDT Methods

💧

Dye Penetrant

📡

Ultrasonic

☢️

Radiography

🌀

Eddy Current</div> </div>

🎤

Acoustic Emission</div> </div>

🧲

Magnetic Particle</div> </div> </div>

Method	Sensitivity	Materials	Defects Detected
Ultrasonic	0.5-5% wall thickness	All	Internal, subsurface
Radiography	1-2% thickness	All	Volumetric
Magnetic Particle	Surface breaking	Ferromagnetic	Cracks, laps

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