Forging: Overview and Techniques

Forging: General Overview

• Forging is a manufacturing process shaping metal using localized compressive forces.
• Forces are delivered using a hammer or die (often power hammer).
• Forging produces discrete parts (rolling: continuous).

Types of Forging

• Open-Die Forging:
  • Simplest forging operation.
  • Parts range from small (pins, nails) to large (ship propellers).
  • Metal workpiece (blank) placed between flat dies, compressed, increasing diameter.
• Closed-Die Forging:
  • Workpiece takes shape of die cavity during forging between shaped dies.
  • Usually done at elevated temperatures for lower forces and improved metal ductility.
  • Material flows outward, forming a flash (in some cases).
  • Flash ensures material completely fills the die cavity
• True Closed-Die Forging (Flashless Forging):
  • Workpiece fills the cavity completely, no flash formed.
  • Proper die design & blank control are crucial for desired dimensions & no material issues.

Forging - Effect on Structure

• Grain flow in components differs based on the process (cast, machined, forged).
• Forged parts generally have good strength and toughness.
• Grain flow in forged parts is controlled, crucial in highly-stressed and critical applications.

General Characteristics of Forging Processes

• Open Die: Simple and inexpensive, wide range of part sizes, good for small quantities. Limited to simple shapes, low material utilization, low production rate, machining required.
• Closed Die: Good material utilization, often better properties than open die, good dimensional accuracy, high production rates and reproducibility. Relatively high die costs, not ideal for low quantities, machining may be required.
• Blocker: Low die costs, high production rates, high material utilization, machining to final shape required. Requires much less machining overall.
• Conventional: High production rates, good material utilization, requires much less machining compared to other types.
• Precision: Close dimensional tolerances, generally does not require further machining. Very good material utilization. High forging forces, intricate dies are needed.

Forging - Materials

• Forgeability is a material's ability to undergo deformation in forging without cracking.
• Different metals (like aluminum, magnesium, copper alloys) have varying hot forging temperature ranges (e.g. Aluminum 400-550 °C, Titanium alloys 700-950 °C).
• Die materials need strength, toughness, and hardenability at elevated temperatures, good resistance to mechanical and thermal shocks, high wear resistance (to abrasions during hot forging).