Numerical and Experimental Analysis of the Powder Flow Streams in the Laser Aided Material Deposition Process

Abstract

Axial powder stream concentration between the nozzle end and the deposition point is an important process parameter in the laser aided material deposition process. The powder concentration is greatly influenced by the nozzle geometry in use. This paper describes the numerical and experimental analysis of this important parameter in relation to the coaxial nozzle. The experiments are performed with the different nozzle geometries to generate various flow patterns of the gravity fed powder in a cold stream. The results of the experimental analysis are compared with the numerical simulation and found justified. These results are used in concluding the significance of important nozzle parameters for various powder concentration modes. Introduction Laser deposition process consists of feeding the metal powder into a hot spot called as melt pool to form a melted zone which solidifies into a bead. The coaxial nozzle is widely used for this metal deposition process [3, 9]. The metal powder is fed through the nozzle in the melt pool in a coaxial system instead of the external tubes as in the side nozzle. Laser aided deposition quality largely depends on the powder stream structure below the nozzle [7]. The variation of the powder stream concentration in axial direction affects the material delivery rate at the deposition point and the interaction of the laser beam radiation with the powder stream [4]. High efficiency of the powder deposition in a coaxial system is an important subject for the study. The focusability of the stream structure is a key factor of the energy utilization and catchment efficiency of the coaxial nozzle [5]. It is found that most of the laser power reaches the substrate with some energy loss in the particles in laser deposition process [9]. This is sometimes caused by the shadow effect of one particle over another due to the absorption of the beam energy by the powder stream. The stream structure is mainly influenced by the powder flow settings and nozzle arrangements [5]. It is also found that the powder catchment increases with increase in the powder flow velocity [9]. The process of deposition involves control of various parameters like powder type, powder flow velocity and gas velocities. Though these are actual process parameters, the initial powder flow is defined by the nozzle geometry in use. Thus, optimizing the deposition nozzle for such process is not an easy task and hence requires a lot of experimentation and numerical simulation. It is difficult to find the literature explaining about the effect of nozzle geometry at the powder outlet area of the coaxial nozzle on the powder concentration mode. Though the above mentioned studies have been carried out, the detailed study needed to be done entailing the effect of the nozzle geometry at the powder passage on the flow mode. The initial consideration should be given in generating various types of powder streams by using different nozzle geometries at the powder outlet area. It is necessary to understand the proper powder flow behavior to determine the displacement of the powder between the nozzle and deposition point. This will help in getting the value for the distance of maximum concentration point of the merging streams