Unit 4: Bulk Deformation

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Sections

Quick Formula Reference
True Stress
σ = F / A
Forging Force
F = σf × A × Kf
Reduction Ratio
r = ((t₀ - tf) / t₀) × 100
Practice Problems
50+ ProblemsBulk Deformation
1

Hot vs Cold Working

Section 1 of 7

Metal Working Processes

Metal forming processes are classified based on the working temperature relative to recrystallization temperature.

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Hot Working

Above recrystallization temperature

Advantages:
Low deformation energy
High production rate
Metal becomes tougher
No work hardening
❄️

Cold Working

Below recrystallization temperature

Advantages:
Better surface finish
Close tolerances
Increased strength
No heating required
Bulk Deformation - Advanced Study Material

Deformation Theory & Mechanics

Stress-Strain Relationships:
  • • True Stress: σ = F/A (instantaneous area)
  • • True Strain: ε = ln(l/l₀)
  • • Flow Stress: σf = Kεⁿ (power law)
  • • Strain Rate: ε̇ = dε/dt
Hot vs Cold Working Criteria:
  • • Recrystallization Temperature: Tr = 0.4Tm (absolute)
  • • Hot Working: T > 0.6Tm
  • • Cold Working: T < 0.3Tm
  • • Warm Working: 0.3Tm < T < 0.6Tm

Process Calculations

Forging Force: F = σf × A × Kf (shape factor)
Rolling Force: F = μ × R × w × Δh × Qp
Extrusion Pressure: P = σf × ln(A₀/Af)
Drawing Force: F = σf × Af × ln(A₀/Af)
Reduction Ratio: r = (t₀-tf)/t₀ × 100%

Comprehensive Exam Questions

Q: Calculate forging force for steel billet (σf=200MPa, A=100cm², Kf=1.5)
A: F = 200×100×1.5 = 30,000 N = 30 kN
Q: Determine if process is hot/cold working for steel at 800°C (Tm=1538°C)
A: T/Tm = (800+273)/(1538+273) = 0.59 → Warm working
Section Summary
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Key Concept
Hot vs Cold Working
🏭
Industry Application
Metal Forming
⚙️
Learning Outcome
Process Selection