مدل پیش بینی عمق مذاب برای کنترل کیفیت لیزر جداره سطح در مواد ناهمگن

This paper reports on an investigation into the development of an analytical model for the quality control of laser marking/engraving of clay tiles using a high-power diode laser (HPDL). An analytical model for the laser melting of inhomogeneous workpieces with parabolic melt pool geometry being assumed was developed. The theoretical results were compared with the experimental data. The predicted melt pool depth and the experimental values were in close correlation with the parameter View the MathML source for values less than View the MathML source, in spite of simplifications introduced in the model. At the relatively large values of parameter View the MathML source the assumption of parabolic melt pool shape and one-dimensional heat transfer no longer holds true.

The development of an accurate analysis procedure for laser applications, including marking/glazing of building materials, is extremely complicated due to many process parameters involved. Variations in the quality of the marking process may be observed between processing cycles performed with the same laser equipment, and apparently constant operating conditions and material properties. This poor reproducibility arises from the high sensitivity of the laser marking process to small changes in the operating parameters (such as laser power and beam velocity stability), as well as to process disturbances (such as varying absorptivity, surface texture changes, geometry changes and workpiece thickness changes). Therefore, monitoring and control of the laser marking parameters are necessary. The parameters that can be measured on-line include melt pool surface temperature and melt pool surface area. The development of a suitable model to predict these parameters can provide knowledge of process performance as well as the prediction of the marking process. This paper presents an analytical model for the melt pool depth geometry in case of high-power diode lasers (HPDL) engraving of clay tiles. High-power diode lasers (HPDL) are emerging as an alternative to “traditional” laser systems in applications other than the medical field. With the availability of fibre-delivered laser systems up to 120 W-cw output power, with focused spot sizes down to View the MathML source diameter and for stacked systems of up to View the MathML source cw with a View the MathML source beam spot, they are fast becoming an alternative method for material processing [1], [2] and [3]. Li et al. [4] studied the basic mechanisms and the characteristics of the beam absorption in case of laser marking/engraving building materials such as: marble, bricks, granite, ceramic tiles, etc. This work considered the effects of glazing mechanisms, material texture, colour, laser process parameters and atmospheric conditions on the marking process. The present paper looks into the optimal operational parameters that will help design a model for controlling the quality of the laser marking/glazing process. Lawrence [5] has developed an analytical model capable of modelling the ceramic tile grout sealing process. He has considered an ABAQUS FEM model for temperature prediction and compared it with the temperature profile, predicted by Carslaw and Jaeger [6]. This actual paper seeks to develop a model for laser glazing clay tiles based on the variation of the melt pool geometry rather than temperature. It has been demonstrated that the relative increase of the melt pool area, due to an increase in laser power, is much larger than the relative increase of the melt pool temperature [7]. This result supports this idea that the melt pool area is the right parameter for the feedback control. Understanding the physical phenomena that occur during laser marking/glazing is relevant for modelling the process. The models resulting from the conservative of energy (heat conduction energy) are used to analyse the effects of the laser power and beam traverse velocity on the temperature distribution and melt pool dimensions. The results from this analysis would be used for the design of a closed-loop control system.

In this paper the quality control of laser marking/engraving of clay tiles using a HPDL has been investigated. The relevant physical phenomena, which occur during laser marking/glazing, were discussed. An analytical model with quasi-stationary situations in an isotropic and inhomogeneous workpiece with a parabolic melt pool geometry being assumed, was successfully developed. The predicted melt pool depth and the experimental values were in relatively good agreement, in spite of simplifications introduced during modeling, for values View the MathML source. The melt pool depth was found to be linearly dependent on the ratio View the MathML source. This also agrees with the discovery of Courtney [16] and Römer [7] for metals. It is believed that this observed increasing discrepancy could be attribute to the inhomogeneous substrate of the clay tiles and to the fact that the model developed neglects sideways conduction energy.