Forging can be classified into different types based on temperature, method, and equipment used. Each type of forging is chosen to achieve specific shapes, strengths, and material properties for various applications.

Types of Forging

Forging is a metal forming process in which compressive forces are used to shape metal into desired shapes. It improves the strength, toughness, and reliability of components because the metal’s grain structure aligns with the part geometry.

Forging can be classified based on temperature, method, and type of equipment. Here’s a detailed explanation:

1. Based on Temperature

A. Hot Forging

Definition: Forging performed above the metal’s recrystallization temperature.
Typical Temperature:
- Steel: 950–1250°C
- Aluminum: 350–500°C
- Copper: 700–900°C
Characteristics:
- Metal is soft and ductile.
- Easier to deform large sections.
- Reduces risk of cracks.
Applications: Automotive components, crankshafts, large shafts, aerospace parts.
Advantages: High ductility, large deformation possible, less force required.
Disadvantages: Scale formation, lower dimensional accuracy, energy-intensive.

B. Cold Forging

Definition: Forging performed below the recrystallization temperature, often at room temperature.
Characteristics:
- Requires higher force than hot forging.
- Produces better surface finish and dimensional accuracy.
- No oxidation or scaling occurs.
Applications: Bolts, nuts, fasteners, small shafts, precision tools.
Advantages: Excellent surface finish, precise dimensions, strain hardening improves strength.
Disadvantages: Limited to small parts, requires high force, risk of cracking for low ductility metals.

C. Warm Forging

Definition: Forging performed at moderate temperatures, between cold and hot forging.
Temperature Range: Typically 30–50% of metal’s melting point.
Applications: Automotive parts (like connecting rods), medium-sized steel parts.
Advantages: Balance between ductility and dimensional accuracy.
Disadvantages: Requires heating equipment, less precision than cold forging.

2. Based on Forging Method

A. Open-Die Forging (Smith Forging)

Definition: The metal is placed between flat or simple-shaped dies, and hammer or press blows shape it.
Characteristics:
- Metal flows freely except where constrained.
- Usually done hot, for large parts.
- Operator skill plays a major role.
Applications: Shafts, rods, disks, aircraft landing gear components.
Advantages: Simple die design, suitable for large parts.
Disadvantages: Less precise, requires skilled operator.

B. Closed-Die Forging (Impression Die Forging)

Definition: Metal is placed in a die cavity, and hammer or press compresses it, forcing the metal to fill the cavity shape.
Characteristics:
- Die contains the negative of the part shape.
- Requires trimming of excess metal (flash) after forging.
Applications: Gears, connecting rods, crankshafts, automotive components.
Advantages: High dimensional accuracy, good surface finish, mass production possible.
Disadvantages: Higher die cost, less suitable for very large parts.

C. Seamless Ring Forging

Definition: Metal billet is pierced and rolled into a hollow ring.
Characteristics:
- Produces rotationally symmetrical hollow parts.
Applications: Bearings, flanges, pressure vessels, pipelines, gears.
Advantages: Strong grain flow along part geometry, uniform properties.
Disadvantages: Limited to ring-shaped parts.

D. Impression Die / Flashless Forging

Flashless Forging: No flash is allowed; die completely encloses the metal.
Application: Precision parts, small components, high-value alloys.

3. Based on Equipment

A. Hammer Forging

Definition: Uses mechanical or power hammers to apply repeated blows.
Applications: Shafts, rods, tools, and railway components.
Characteristics: High speed impact, suitable for open-die forging.

B. Press Forging

Definition: Uses a hydraulic or mechanical press to apply continuous force.
Applications: Gears, aerospace components, large dies.
Characteristics: Slow, controlled deformation, better internal metal flow, suitable for closed-die forging.

C. Roll Forging

Definition: Metal passes between grooved rolls, reducing cross-section.
Applications: Shafts, rails, strips.
Advantages: Efficient for long parts, uniform cross-section.

4. Special Types of Forging

Isothermal Forging
- Die and workpiece are kept at the same high temperature.
- Used for superalloys like aerospace turbine components.
Precision Forging
- Near-net shape forging for small, high-precision parts.
- Reduces machining operations.
Upset Forging
- Increases diameter of a part by compressing length.
- Common in bolts, shafts, and fasteners.
Drop Forging
- Part is formed by free-falling hammer on a hot metal.
- Rapid and widely used for mass production.

5. Summary Table of Forging Types

Type	Method	Temperature	Applications	Advantages	Disadvantages
Open-die Forging	Flat dies	Hot	Shafts, rods, large parts	Simple, large parts	Low accuracy
Closed-die Forging	Cavity dies	Hot	Gears, crankshafts	High accuracy, good finish	High die cost
Seamless Ring Forging	Piercing + rolling	Hot	Rings, bearings	Strong grain flow	Limited shape
Cold Forging	Room temp	Cold	Fasteners, bolts	High accuracy, surface finish	Limited size
Warm Forging	Moderate temp	Warm	Automotive parts	Balance of strength and accuracy	Equipment required
Hammer Forging	Repeated blows	Hot	Shafts, tools	Simple, fast	Less control
Press Forging	Hydraulic/Mechanical press	Hot	Gears, aerospace	Controlled deformation	Slower process
Roll Forging	Grooved rolls	Hot/Cold	Rails, strips	Efficient for long parts	Limited shapes
Upset Forging	Compress length to increase diameter	Hot	Bolts, shafts	Strong components	Limited shape
Isothermal Forging	Die and part same temp	Hot	Aerospace superalloys	Minimal stress	Expensive
Precision Forging	Near-net shape	Hot	Small, high-value parts	Less machining	Costly dies

In Simple Words

Forging can be done hot, cold, or warm, using hammers, presses, or rolls. Open-die forging is simple and flexible, closed-die forging gives high-precision parts, and special methods like ring forging or upset forging are used for specific shapes.