Jawaharlal Nehru Technological University Hyderabad B.Tech III MANUFACTURING PROCESS AND MACHINE TOOLS Previous Question Paper (February - 2022 - R18)

Laser Beam Welding (LBW) is a fusion welding process that uses a highly concentrated, coherent beam of light to join metal parts. The process relies on a laser source (such as CO2 or Nd:YAG) to generate a high-energy density beam, which is focused by lenses onto the joint interface. The intense heat causes instantaneous melting and vaporization of the material, creating a deep, narrow weld pool with minimal heat-affected zone (HAZ).

Key components include the laser source, beam delivery system (mirrors and lenses), shielding gas nozzle, and workpiece fixture. The process is characterized by high welding speeds, deep penetration, and low thermal distortion. It is widely used in automotive and electronics industries for precision applications.

Solidification of casting is the phase transformation process where molten metal transitions into a solid state within a mold. It occurs in three distinct stages: nucleation, crystal growth, and the formation of the final grain structure. As the molten metal loses heat to the mold walls, nuclei form at the surface (chilled zone), followed by the growth of columnar grains directed toward the thermal center, and finally, the formation of equiaxed grains in the center.

The importance of understanding solidification includes:

• Microstructure Control: The cooling rate directly determines grain size and distribution, which dictates the mechanical properties like strength and ductility.
• Defect Prevention: Proper control of solidification prevents common defects such as shrinkage cavities, porosity, and hot tearing caused by non-uniform cooling.
• Dimensional Accuracy: Managing the solidification shrinkage ensures that the final casting meets the required geometric tolerances.
• Segregation Management: It helps in minimizing chemical heterogeneity (solute redistribution) within the casting, ensuring uniform performance.