Forging Process Quiz

Forging

• Forging is a metal forming process using compressive forces applied through dies and tooling to shape the workpiece.
• Forged parts exhibit high strength and toughness, making them suitable for critical applications.
• Heating the workpiece at high temperatures (warm or hot forging) improves metal plasticity and reduces the force and energy needed during the process.
• Forged parts include engine crankshafts, connecting rods, gears, aircraft structural components, and jet engine turbine parts.
• Forging operations produce rough forms, requiring subsequent operations to refine the part's geometry and dimensions.
• Open-die forging uses flat dies, allowing metal to flow laterally without constraint. This method produces rough and simple shapes.
• Closed-die forging uses two dies, producing a more complex shape. The workpiece fills the die cavity. Metal may flow outside the die cavity (flash).

Forging Operations

• Open-die forging (e.g., upsetting, cogging, bar forging, and ring forging)

  • Upsetting: Shortening a workpiece and increasing its cross-section.
  • Cogging: Reducing the thickness of a long workpiece.
  • Bar forging: Reducing the diameter of a cylindrical workpiece.
  • Ring forging: Reducing the diameter of a cylindrical workpiece to make rings or discs.

• Close-die forging: (e.g., impression-die forging, flashless forging)

  • Impression-die forging: Completely deforming the workpiece within a closed die cavity. A flash of excess material is produced which is trimmed later.
  • Flashless forging: The workpiece is fully constrained in the die cavity, preventing flash. This is typical of cold working processes.

Forging steps

• Preparation of raw material (e.g., billet, ingot)
• Heating of raw material (only for hot forging)
• Removal of scale from work surface (if necessary) to avoid scale embedding in the work
• Preheating (only for hot forming) and lubrication of dies
• Forging material
• Other (possible) forming operations
• Cleaning
• Dimensional control
• Machining operations (if necessary)
• Heat Treatment (if necessary)
• Final control (e.g., final tests, dimensional control)

Forging temperatures

• Specific temperature ranges for various metals are necessary for optimal forging outcomes. The values are given in °C and °F. A table lists the temperature ranges for various metals.

Types of Forging Operations:

• Open die forging
  • Upsetting
  • Cogging
  • Bar forging
  • Ring forging
• Closed die forging
  • Impression die forging
  • Flashless forging

Other Forging Operations

• Heading: Increasing the cross-section of a cylindrical workpiece near its end.
• Edging: Redistributing metal flow to prepare work for subsequent forming operations.
• Piercing: Creating a cavity in a metal workpiece by indenting with the punch.
• Orbital/Rotary forging: Using rotating dies to shape the workpiece incrementally.
• Roll forging: Shaping a workpiece using opposing rolls with grooved surfaces.
• Radial forging/Swaging: Reducing the diameter of a tube or rod.
• Production of ball bearings
• Trimming after forming removes excess metal flash.

Forging Defects

• Cracks: Due to excessive stress during forming.
• Unfilled defects: Inappropriate die design or insufficient metal volume causing uneven material distribution.
• Mismatch: Die misalignment in the register, leading to errors in the final product.
• Flakes: Internal ruptures in the forged part caused by improper cooling.
• Scale pits: Surface flaws often caused by improper cleaning of the stock.

Closed-die forging design

• Essential considerations: parting line, draft angles, corner/fillets radii, initial billet dimensions, and material allowance.
• Parting line: Crucial for ease of component removal.
• Draft angles: Essential for removing the forged part from the dies.
• Corner and fillet radii: Prevent flaws (like cracks, laps, and cold shuts.).
• Initial billet dimensions: Ensuring sufficient volume ensures complete filling of the die cavity.
• Material allowance: Calculating sufficient material beyond part dimensions for machining to desired specifications.
• Temperatures during various stages of the process.

Other Aspects in Forging Operations

• Material formability: Not all materials are suitable for forging due to their formability. Brittle materials are unsuitable for forging, since they break before they reach the desired deformation
• Flow of Metal: The flow of workpiece material during the operation, and the geometrical features of the die cavity determine the shape of the final product.
• Friction: The use of lubricants reduces friction when necessary to have a more constant material flow.
• Die temperature: Preheating of dies, in hot forging, helps to decrease forming pressure, improve the quality of the operation, and avoid die damage.
• Shrinkage stress: During cooling, the material shrinks and can put strain on the part.
• Impossibility of through holes: In closed-die forging designs, the thickness of the material around the hole is greater than the thickness of the land.
• Material allowance: Important for machining the forged product to the precise dimensions.

Forging Load and Energy

• Forging load depends on workpiece material (cold working leads to increase in strain hardening).
• Hot forging doesn't exhibit work hardening.
• Calculations for forging load and energy are typically empirical (using the calculated mean flow stress and area of the part to estimate the force required).

Test your knowledge on the forging process, including its purposes, characteristics of forged parts, and the machinery involved. This quiz covers key concepts such as heating requirements, lubrication effects, and flow stress evaluation.