Lesson 8.2: Metal Forming (Forging, Rolling, Drawing, Extrusion)

Metal forming is a core manufacturing process. GATE and PSU exams often test different forming methods, principles, and applications.

🔹 1. Introduction

• Definition: Metal forming is the process of shaping metals by plastic deformation without removing material.

• Applications: Engine components, shafts, rods, sheets, tubes

• Key Concepts: Forging, rolling, drawing, extrusion, deformation mechanics

🔹 2. Forging

• Definition: Shaping metal using compressive forces

• Types:

  1. Open-die forging – Metal deformed freely

  2. Closed-die forging – Metal confined in die cavity

  3. Roll forging – Metal passed through rolls for shape reduction

• Applications: Shafts, gears, connecting rods

• Advantages: High strength, improved grain structure

🔹 3. Rolling

• Definition: Metal thickness reduced by passing between rotating rolls

• Types:

  1. Hot Rolling – Metal above recrystallization temperature

  2. Cold Rolling – Metal below recrystallization temperature

• Applications: Plates, sheets, rails, structural sections

• Key Concepts: Roll force, spread, elongation, thickness reduction

🔹 4. Drawing

• Definition: Metal pulled through dies to reduce cross-section

• Types: Wire drawing, tube drawing

• Applications: Wires, rods, tubes

• Advantages: Accurate cross-section, improved surface finish

🔹 5. Extrusion

• Definition: Metal forced through die opening to obtain desired shape

• Types: Direct extrusion, indirect extrusion, hydrostatic extrusion

• Applications: Pipes, rods, profiles

• Advantages: Complex cross-sections, good surface finish

🔹 6. Solved Examples (PYQ Style)

1. Identify suitable forming method for a shaft

2. Calculate rolling force for given plate thickness reduction

3. Analyze wire drawing stress and reduction ratio

4. Suggest extrusion process for aluminum profile

🔹 7. Practice Exercises

1. Draw and label forging and rolling processes

2. Compare hot rolling vs cold rolling

3. Solve problems on thickness reduction and roll force

4. Explain advantages of extrusion over drawing

5. List applications of each forming process

🔹 8. Summary

• Metal Forming: Shaping metals via plastic deformation

• Forging: Compressive forces; open and closed die

• Rolling: Thickness reduction; hot and cold rolling

• Drawing: Pulling through dies; wires and tubes

• Extrusion: Forcing metal through die; rods and profiles

• Exam Tip: Focus on process selection, principles, and calculations