Jawaharlal Nehru Technological University Hyderabad B.Tech II AIRCRAFT PRODUCTION TECHNOLOGY Previous Question Paper (March - 2021 - R16)

Centrifugal casting is a manufacturing process where molten metal is poured into a rotating mold, utilizing centrifugal force to distribute the metal against the mold walls. The mold rotates at high speeds about its axis, which can be horizontal, vertical, or inclined, depending on the geometry of the required part.

The process is categorized into three types: true centrifugal casting, semi-centrifugal casting, and centrifuge casting. In true centrifugal casting, the mold rotates about its own axis to produce hollow cylindrical parts such as pipes, tubes, and bushings. The centrifugal force ensures high density and structural integrity by forcing impurities and gases toward the inner surface, which is later machined away. This method eliminates the need for cores and provides excellent grain structure due to rapid solidification against the cooled mold wall.

Solid phase welding is a group of welding processes where coalescence is produced at temperatures below the melting point of the base metals, without the addition of a filler metal. The bonding is achieved through the application of pressure and sometimes heat, facilitating atomic diffusion across the interface.

• Surface Preparation: The mating surfaces must be thoroughly cleaned to remove oxides, grease, and contaminants, as these act as barriers to atomic bonding.
• Application of Pressure: Mechanical force is applied to bring the surfaces into intimate contact, breaking up surface films and allowing atomic forces to act.
• Heating (Optional): In many processes, the workpieces are heated to a temperature below the solidus to increase ductility and promote diffusion, though the metal remains in the solid state.
• Deformation and Bonding: Plastic deformation occurs at the interface, causing the asperities to collapse and creating a metallurgical bond through recrystallization and grain growth across the interface.
• Cooling: The joint is allowed to cool, often resulting in a weld zone that possesses mechanical properties similar to the parent material.

Common examples include forge welding, friction welding, diffusion bonding, and ultrasonic welding.