Week 12_Sheet metal forming, forging and extrusion (1)

AERO4100 - Lecture on Sheet Metal Forming and Related Processes

1. Introduction to Sheet Metal Forming

  • Sheet metal forming involves operations on metal sheets, occurring at room temperature or elevated temperatures.

2. Importance in Aerospace Industry

  • Nearly 50% of airplane parts are produced through sheet forming.

    • Military aircraft: 10,000 to 40,000 parts

    • Commercial aircraft: Up to 60,000 parts

  • Represents about 20% of the total production time in manufacturing airplanes.

  • Considered one of the most advanced manufacturing technologies, significant for evaluating a country's manufacturing capabilities.

3. Characteristics of Formed Parts

  • Parts display:

    • Dimensional variations

    • Complex shapes

  • Special facilities are required for production.

  • Process may lead to high dimensional errors, but high accuracy is needed.

4. Common Sheet Metal Forming Operations

4.1 Sheet Forming

  • Superplastic Forming and Diffusion Bonding (SPF/DB)

  • Shot Peening Forming

  • Spinning Forming

  • Creep Age Forming

  • Hot Forming

  • Stretch Forming

4.2 Bending Operations

  • Press Bending

  • Draw Bending

  • Roll Bending

4.3 Tube Forming

  • Tube End Forming and Joining

  • Tube Bending

  • Expanding and Bending

5. Detailed Analysis of SPF/DB

5.1 Superplasticity of Materials

  • Defined as the ability of materials to undergo significant plastic deformation before necking or fracture (elongations up to 2000%).

  • Exhibited in alloys such as:

    • Aluminium Alloys: 7475, 2004, 5083, 8090, 2090, 1420

    • Titanium Alloys: Ti64, Ti6242, Ti55, SP700

5.2 Mechanisms of Superplasticity

  • Grain boundary gliding, grain rotation, and dislocation movements contribute to superplasticity.

  • Superplasticity alloys typically exhibit low flow stress.

5.3 SPF Processes

  • A heated sheet is placed in a die, clamped, and gas pressure is applied to form the desired shape.

  • Back-pressure can mitigate cavity formation during deformation in aluminum alloys.

5.4 Diffusion Bonding (DB)

  • A joining process reliant on atomic diffusion at elevated temperatures (0.5-0.7 Tm).

  • Requires moderate gas pressure for effective bonding and is typically carried out under vacuum conditions.

  • Surfaces must possess specific roughness for effective bonding.

6. Shot Peening Forming

  • Utilizes mechanical impact to induce compressive residual stresses on components, leading to deformation and shape changes.

  • Types include centrifugal, pneumatic, and supersonic peening.

  • Applications include integrated panels for aircraft wings.

7. Creep Age Forming (CAF)

  • Involves forming an aluminum plate under creep conditions while simultaneously undergoing aging treatment.

  • Conducted in a vacuum and encompasses multiple stages including pressurizing, shaping, heating, and unloading.

8. Metal Spin Forming

  • A high-speed forming method involving rotating metal discs or tubes around a mandrel.

  • Can create axisymmetric parts without removing material, utilized for various aerospace components including ducts and nozzles.

9. Stretch Forming

  • A process where sheet metal is stretched and bent over a die to create contoured parts.

  • Operated through a stretch press using hydraulic or pneumatic forces, forming a wide range of materials including aluminum and titanium alloys.

10. Conclusion and Key Points

  • Understanding various sheet metal forming techniques:

    • Superplasticity and its mechanisms

    • SPF/DB applications

    • Shot peening and its effects

    • Overview of CAF, Metal spin forming, and Stretch forming processes.

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