Heat and Fluid Flow

Summary

The heat and fluid flows that occur during laser processing influence the microstructures, residual stresses, and distortion that evolves during the process. These in turn affect the mechanical properties and thus quality of the process. This chapter presents simplified lumped parameter energy balance equations that enable quick estimates to be made of energy requirements for a given process. It considers heat flow in the solid part of the workpiece. The chapter discusses flow in the molten pool for processes that involve melting. The discussion on the temperature distribution starts with the governing equation for conduction heat flow. This is based on the assumption that heat conduction through the workpiece is usually much greater than any heat exchange with the surroundings by natural convection or radiation. Fluid flow in the molten pool affects the structure and properties of the fused zone, such as the geometry, surface smoothness, porosity, lack of fusion, undercutting, solidification structure, and macrosegregation.