Concentration model based on movement model of powder flow in coaxial laser cladding

https://doi.org/10.1016/j.optlastec.2008.03.008Get rights and content

Abstract

The structure below the coaxial nozzle is critical since the spatial distribution of metal powder particles determines the laser attenuation as well as catchment efficiency. It is difficult to simulate the powder concentration distribution, because the complex phenomena involved in the two-phase turbulence flow. In this paper, the air-powder flow is studied along with powder properties, nozzle geometries and shielding gas setting. A Gaussian model is established to quantitatively predict the powder stream concentration in order to facilitate coaxial nozzle design optimizations. An experimental setup is design to measure the powder concentration for this process. The simulated results are compared with the experimental results. This study shows that the powder concentration mode is influenced significantly by powder properties, nozzle geometries and shielding gas setting.

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]:f(x,y,z)=m(y)2πδ2exp[-x2+z22δ2]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)

  • Liu J.

    Effects of powder concentration distribution on fabrication of thin-wall parts in coaxial laser cladding

    Opt Laser Technol

    (2005)
  • Liu J.

    Study on cross-section clad profile in coaxial single-pass cladding with a low-power laser

    Opt Laser Technol

    (2005)
  • Liu J.

    Formation of cross-sectional profile of a clad bead in coaxial laser cladding

    Opt Laser Technol

    (2007)
  • Liu J. 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)
  • Onwubolu G.C.

    Prediction of clad angle in laser cladding by powder using response surface methodology and scatter search

    Opt Laser Technol

    (2007)
  • Lin J.

    Concentration model of the powder stream in coaxial laser

    Opt Laser Technol

    (1999)
There are more references available in the full text version of this article.

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