Concentration model based on movement model of powder flow in coaxial laser cladding
Introduction
The quality and efficiency of laser-aided direct metal deposition largely depends on the powder flow structure below the nozzle. Operating parameters such as powder properties, nozzle geometries and shielding gas setting should be optimized based on the understanding of the powder concentration distribution.
Some researches were done in this field. Model of effects of powder concentration distribution on fabrication of thin-wall parts in coaxial laser cladding was developed by Liu et al. [1]. They defined the static model of powder mass concentration distribution at cold-stream conditions in coaxial single-pass cladding with a low-power laser as a Gaussian function [2]. They also investigated formation mechanism of cross-sectional profile of a clad bead in coaxial laser cladding [3], and presented in-time adjustment in laser cladding manufacturing process as a means to improve dimensional accuracy and surface finish of the built part [4]. An experimental investigation of the influence of processing parameters on clad angle in laser cladding by powder was presented by Onwubolu et al. [5], and the movement model and thermal model of powder particle in coaxial laser cladding is proposed by Lin [6], [8].
In this paper, an investigational approach is described which includes simulation method and experimental setup. This simulation methodology considers more general conditions and has the potential for optimization of powder flow for coaxial laser cladding. A precise and low-cost optical measuring system and its application are also included.
Section snippets
Movement model
The powder stream with shield gas output from the annular nozzle can be divided into three regions by AA′ and BB′. The longitudinal section of the annular nozzle and the powder stream are shown in Fig. 1, where w is the nozzle exit width, r is the nozzle inward wall radius, α is nozzle angle and φ is powder divergence angle. In order to establish powder particle movement model, some assumptions should be illustrated [8], [9], [10], [11]:
- (1)
A powder particle is moving in a uniform gas flow, and its
Concentration model
In this paper, the powder flow concentration distribution in regions 2 and 3 is more concerned than region 1, as shown in Fig. 1, and the concentration of powder is expressed by volume fraction. We suppose that the 3D distribution of the powder particles’ number in regions 2 and 3 could be expressed by the Gaussian function [12]:where f(x, y, z) is powder particles number 3D distribution function, m(y) is powder particles number vertical distribution function: the
Experimental research
Direct measurement of powder concentration is impossible. Therefore, the powder volume fraction could be measured by an image processing technique. Typical image-based technique for studying small particle motions in carrier gas is PIV [13]. The principle and devices of experiment are shown in Figs. 9(a) and (b). The image of powder stream taken by CCD camera is shown in Fig. 9(c). The parts of measurement system are as follows: YAG pulse laser, 2D sheet of light lens, CCD camera, etc.
Double
Conclusions
Based on movement model, a Gaussian concentration model in more general conditions is proposed to simulate the volume fraction distribution of powder particle stream under different process parameters in coaxial laser cladding.
It is found that the powder parameters such as particle velocity and mass flow rate influence the powder stream configuration and concentration distribution. The nozzle geometries influence powder flow structure and concentration distribution. The nozzle exit width
Acknowledgments
This project was supported by National Natural Science Fund of China (No. 6047804) and Key Project of Tianjin Science and Technology Committee (No. 033188011).
References (12)
Effects of powder concentration distribution on fabrication of thin-wall parts in coaxial laser cladding
Opt Laser Technol
(2005)Study on cross-section clad profile in coaxial single-pass cladding with a low-power laser
Opt Laser Technol
(2005)Formation of cross-sectional profile of a clad bead in coaxial laser cladding
Opt Laser Technol
(2007)- et al.
In-time motion adjustment in laser cladding manufacturing process for improving dimensional accuracy and surface finish of the formed part
Opt Laser Technol
(2004) Prediction of clad angle in laser cladding by powder using response surface methodology and scatter search
Opt Laser Technol
(2007)Concentration model of the powder stream in coaxial laser
Opt Laser Technol
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2021, International Journal of Mechanical SciencesCitation Excerpt :Instead of using complicated numerical models, Pinkerton and Li developed and experimentally validated an analytical model for estimating the powder concentration distribution in an unobstructed stream of powder jet [9]. Subsequently, few analytical models were developed to estimate the powder distribution in the vicinity of the focal plane, taking into account carrier gas flow and the powder stream divergence [10–13]. However, these models do not incorporate the effect of gravity on the powder flow dynamics.