Rolling vs Forging vs Extrusion vs Drawing

Metal forming processes are used to shape metals into desired sizes and shapes by applying mechanical forces. Among the most common processes are rolling, forging, extrusion, and drawing. Rolling compresses metal between rotating rolls to produce sheets and plates.

Forging shapes metal using compressive forces to improve strength and toughness. Extrusion forces metal through a die to produce long profiles with uniform cross-section. Drawing pulls metal through a die to reduce cross-section and improve dimensional accuracy and surface finish. Each process has its unique advantages, limitations, and applications in manufacturing.

Here’s a detailed comparison of rolling, forging, extrusion, and drawing, covering principle, force type, temperature, product shape, material, advantages, and limitations. This is very useful for exam or industrial reference.

1. Definition of Each Process

Process	Definition
Rolling	Metal is passed between rotating rolls to reduce thickness or change cross-section.
Forging	Metal is shaped by compressive forces, usually using a hammer or press.
Extrusion	Metal is pushed or pulled through a die to produce long products with uniform cross-section.
Drawing	Metal is pulled through a die to reduce cross-section and increase length, mainly under tensile stress.

2. Type of Force Used

Process	Force Type
Rolling	Compressive (between rolls)
Forging	Compressive (hammer or press)
Extrusion	Compressive (ram pushes metal through die)
Drawing	Tensile (metal is pulled)

3. Temperature of Operation

Process	Cold / Hot	Notes
Rolling	Hot or Cold	Hot rolling above recrystallization; cold rolling below it
Forging	Hot, Warm, or Cold	Hot forging for steels, cold forging for softer metals
Extrusion	Hot, Warm, or Cold	Hot extrusion for steel, cold extrusion for aluminum, lead, copper
Drawing	Mostly Cold	Cold drawing preferred; hot drawing for difficult materials

4. Material Form

Process	Typical Material Form
Rolling	Slabs, plates, sheets, ingots
Forging	Billets, ingots, bars
Extrusion	Billets, rods, powders (for metal)
Drawing	Rods, wires, tubes, sheets

5. Product Shapes Produced

Process	Shapes
Rolling	Plates, sheets, strips, rails, beams
Forging	Shafts, gears, hand tools, automotive parts
Extrusion	Rods, tubes, bars, profiles, channels
Drawing	Wires, rods, bars, tubes, cups (sheet metal drawing)

6. Mechanism of Metal Flow

Process	Metal Flow
Rolling	Metal is compressed and flows in rolling direction
Forging	Metal flows to fill die cavity
Extrusion	Metal flows through die opening, same or opposite direction of ram
Drawing	Metal flows along die axis, pulled under tensile stress

7. Dimensional Accuracy & Surface Finish

Process	Accuracy	Surface Finish
Rolling	Moderate	Good (cold rolling better)
Forging	Moderate	Fair to good
Extrusion	High	Good (hot extrusion moderate, cold extrusion excellent)
Drawing	Very High	Excellent

8. Reduction per Pass / Deformation

Process	Reduction Type
Rolling	Large reduction possible, in multiple passes
Forging	Limited by hammer / press capacity; complex shapes
Extrusion	Large reduction ratio possible (up to 8–10 for hot extrusion)
Drawing	Limited reduction per pass; multiple passes with annealing needed

9. Mechanical Property Effects

Process	Effects
Rolling	Improves grain structure, increases strength in rolling direction
Forging	Enhances strength, toughness, and fatigue resistance due to directional grain flow
Extrusion	Refines grains, reduces porosity, improves ductility
Drawing	Work hardening increases strength; surface finish improves

10. Advantages

Process	Key Advantages
Rolling	High production rate, good surface finish, suitable for large sheets/plates
Forging	Excellent strength, directional grain flow, reduced porosity
Extrusion	Can produce complex cross-sections, continuous lengths, uniform properties
Drawing	Very accurate dimensions, smooth surface, high mechanical strength

11. Limitations

Process	Limitations
Rolling	Limited shapes (flat, simple), high friction, requires multiple passes
Forging	High tooling cost, complex dies expensive, limited shape complexity
Extrusion	High initial cost, die wear, poor surface finish (hot)
Drawing	Limited reduction per pass, requires annealing, tensile stress can cause fracture

12. Applications

Process	Typical Products
Rolling	Steel plates, sheets, rails, beams
Forging	Crankshafts, connecting rods, hand tools, turbine blades
Extrusion	Aluminum profiles, pipes, rods, heat sinks
Drawing	Electrical wires, rods, tubes, cups, thin-walled shells

13. Summary Table

Feature	Rolling	Forging	Extrusion	Drawing
Force Type	Compressive	Compressive	Compressive	Tensile
Temperature	Hot/Cold	Hot/Warm/Cold	Hot/Warm/Cold	Cold/Hot
Workpiece Form	Slabs, sheets	Billets, ingots	Billets, rods	Rods, wires, tubes
Product Shape	Plates, sheets	Shafts, tools	Profiles, rods	Wires, tubes, cups
Accuracy	Moderate	Moderate	High	Very High
Surface Finish	Good	Fair	Moderate–Good	Excellent
Material Flow	Rolling direction	Fills die	Through die	Along die axis
Reduction	Large per pass	Limited	Large	Limited per pass
Advantages	High rate, sheets	Strong, tough	Complex shapes	Precise, smooth finish
Limitations	Simple shapes	Costly dies	Die wear	Annealing needed