2025 Forging GPT o3

1. Open-Die Forging: Used for large parts and allows unrestricted metal flow.

2. Closed-Die Forging (Impression Forging): Uses die cavities to produce precise shapes.

Forging produces parts with high mechanical strength due to grain refinement, improved directional properties, and reduced porosity compared to casting.

M describes the triaxiality factor

It is the hydrostatic stress divided throught the mises stress:

(the mises stress describes the multiaxial load)

Oxides form on the surface, which are more prone to cracking. They crack and the oxidized part grows further into the material.

It is used for large-scale metal shaping (e.g., ingots, large billets) and for pre-shaping billets before closed-die forging.

1. Cogging: Reduces the cross-section of a bar.

2. Upsetting: Increases diameter by compressing the bar end.

3. Heading: Forms heads on bolts and fasteners.

4. Additional operations: Bending, drilling, and shearing for further shaping.

1. Hydraulic Presses: Provide large forces with slower operation.

2. Mechanical Hammers: Offer high impact for fast shaping.

1. Preheating the workpiece in a furnace.

2. Preforming (often by cogging or upsetting).

3. Forging the preformed piece in dies (usually in two stages).

4. Removing flash with a trimming die.

5. Applying heat treatment to refine structure.

6. Surface finishing (e.g., sandblasting).

7. Final machining for dimensional accuracy.

Lubrication reduces friction and die wear.

• Cold Forging: Uses mineral oils and lubricants based on MoS₂ or graphite.

• Hot Forging: Uses graphite mixed with water emulsions or glass-based lubricants.

Flash is the excess metal that escapes from the die cavity; it acts as a safety valve for excess material. A thinner flash increases resistance to flow, ensuring the cavity is fully filled while reducing material waste.

1. Shrinkage Compensation: Cavity sizes are increased by ~1% for steels and 0.8–0.9% for copper alloys to account for shrinkage upon cooling.

2. Machining Allowance: An extra 1–2 mm of material is left for finishing operations.

3. Draft Allowance: A 5° taper is incorporated into dies to facilitate part removal.

1. Hydraulic Presses: Deliver forces of 2.2–145 MN at slower speeds (0.06–0.3 m/s), suitable for high-energy operations.

2. Mechanical Presses: Provide forces of 2.2–625 MN at faster speeds (0.06–1 m/s), ideal for high-rate production

It converts rotary motion into reciprocating (linear) motion, allowing for precise strokes during forging.

It is an approach used to account for friction effects at the die–metal interface, resulting in a “friction hill” where stress is higher at the center and lower at the edges.

1. Cold Forging: μ ≈ 0.05–0.10.

2. Hot Forging: μ ≈ 0.1–0.2.

1. Surface Cracks: Caused by tensile stresses and low ductility.

2. Internal Cracks: Resulting from shear banding and high strain rates (e.g., observed in Ti-6Al-4V at 910°C and 30 s⁻¹).

1. Surface Cracks: Due to excessive friction and stress concentrations.

2. Internal Voids: Caused by improper material flow.

3. Geometrical Defects: Often a result of improper flash design.

1. High Ductility: Low-carbon steels, aluminum alloys, copper alloys, and Type 304 stainless steel.

2. Medium Ductility: Nickel-based alloys and high-strength titanium alloys.

3. Low Ductility: Duplex stainless steels and superalloys.

• Very fine grain after normalizing only

  (high strength)

• Thermomechanical treatment (warm

  forging at a controlled temperature), to

  further optimized the grain size (and

  avoid also normalizing).

• not direct (static) recrystallization while hot forging (normalization treatment necessary

  
  

Die wear can occur due to oxidation, thermo-mechanical fatigue, and sliding wear (tribo-oxidation).

Common treatments include nitriding (the most common), PVD and CVD coatings (such as TiN), and hard chromium coatings.