It is widely recognized that the melt flow in weld seam formation occurs under the influence of recoil pressure of vapor. However, the search for such experiments which would have confirmed this hypothesis does not give results. On the contrary, the results of experiments generally contradict this hypothesis:
1. According to the measured results, the pressure in the penetration channel amounts to ~0,001 atm, which is far smaller than the forecasts based on the vaporization hypothesis being in the range of 0.1 – 0.5 atm to several atmospheres.
2. The velocity of vapor effluence under the action of laser radiation of a moderate intensity of ~1 MW/cm2, detected in experiments (10 m/s –45 m/s ), is significantly lower than the forecasts based on the vaporization hypothesis. According to this hypothesis, the value of vapor velocity under laser welding should be comparable with the sound velocity in vapors, that is, higher than 800 m/s.
3. The vaporization hypothesis assumes overestimated values of the rate of weight losses by vaporization. The estimated rates of weight losses in laser welding based on the vaporization model forecast their values in the range of 100–150 mg/s, which significantly exceeds the measured results (2–3 mg/s).
4. In accordance with the vaporization hypothesis, the phenomenon of deep penetration should be accompanied by a drastic increase in the vaporization process. Together with the increase in penetration depth, one should expect an increase in the rate of weight loss. It should be observed for steel at a threshold intensity of deep penetration amounting to ~0.5 MW/cm2. However, in the experiments a drop in weight loss is found at a significantly higher intensity of ~3 MW/cm2 . The existing interval between the threshold of deep penetration and the drop of weight loss in vapor indicates the absence of a cause and effect relationship between these phenomena.
5. In accordance with the vaporization hypothesis, the power consumption for vaporization at laser welding should amount to about 30% of the beam intensity. However, the estimation of this consumption based on the measured values of the rate of weight loss by vaporization (2–3 mg/s) is less than 1%. Such low power consumption for vaporization is confirmed also by the power balance obtained by the use of measurements of efficient and thermal efficiency coefficient of welding, taking into account estimations of intensity loss by thermal conductance. Therefore, the forecasts of power consumption for vaporization (based on the vaporization hypothesis) are not confirmed by the measurements.
Although the presented list of contradictions is not complete, it presents justified grounds for doubting the relevance of the application of the vaporization hypothesis for the simulation of welding hydrodynamic processes.
Dear Rinat Seidgazov, the high welding penetration is essentially described by Maragoni flow of the melted material and the viscosity where the temperature gradients are very important. The vaporization on the surface of welding pool change the speed of liquid in that area and increase the Maragoni classical conditions, in my opinion. Some experiment can be easy made.
Yes, it is. The question is how much is the impact of evaporation on the melt removal in deep penetration laser welding. According to experimental data such a role of evaporation is insignificant. It means that fundamental role plays a mechanism that is not associated with evaporation. I think such a mechanism is the action of capillary forces. If you have a possibility of holding special experiments to decide this problem, I’m willing to discuss a plan of such experiments.
Rinat, Have you read the article cited below? It can be found on ReseachGate
J. Phys. D: Appl. Phys. 34 (2001) 364–372 www.iop.org/Journals/jd PII: S0022-3727(01)16345-X
Modelling of high-density laser–material interaction using fast level set method
H Ki, P S Mohanty and J Mazumder
Robert, thanks for your interest to my question and for the Ref.
The impact of the laser beam with intensity of 10 -100 Mw/cm2 is discussed in this article.
This is 1-2 orders of magnitude higher than the actual values which corresponds to real welding process ( ~1 MW/cm2).
That is why you cannot find the word “welding” in this article.
Thank you again. Another references are welcome.
Http://iopscience.iop.org/0022-3727/32/15/103/pdf/0022-3727_32_15_103.pdf
This article is one of many theoretical works on modeling of laser welding, which is based only on the notion of evaporation hypothesis. Unfortunately, it has been done without any experimental studies of this approach.
The theory of laser-induced evaporation developed by Anisimov was used in this research. This theory was developed for laser radiation with intensity over 100 Mw/cm2. It is more than 2 orders of magnitude exceeds the terms of laser welding.
It should be noted that in simulation of evaporation of metal by laser beam used two approaches - the classical theory of evaporation based on Langmuir equation and Anisimov’s theory of evaporation.
Here are two quotes that describe problems associated with these approaches:
- “experimental data indicate that the vaporization rate under most welding conditions is five to ten times lower that the rate predicted by the Langmuir equation” - T. DebRoy, S. A. David Physical processes in fusion welding. Rev. Mod. Phys., 1995, Vol. 67, No 1.
- “Comparison of the measured values of velocity, acceleration and pressure with those calculated from Anisimov’s theory show very poor agreement. The calculated values are in all cases far larger (by at least an order of magnitude).” - V. V. Semak, G. A. Knorovsky, D. O. MacCallum, D. R. Noble, M. Kanouff. Measurements and Calculation of Recoil Pressure Produced During CO2 Laser Interaction with Ice. International Conference on Lasers and Electron Optics, San Diego, CA (US), 9 Dec 1999
Dear colleagues! The dicussed problem is in center of another my question in RG - What is the real value of vapor pressure inside a keyhole in laser welding or EBW ?
You are welcome to discussion
A few more papers from Hyungson Ki that may be of interest, but I suspect you are probably already familiar with them.
1. A numerical method for multiphase incompressible thermal flows with solid-liquid and liquid-vapor phase transformations
H. Ki*, P.S. Mohanty and J. Mazumder
Numerical Heat Transfer, Part B: Fundamentals, vol. 48, num. 2, 125-145, (2005).
2. Modeling of laser keyhole welding – II. Simulation of keyhole evolution, velocity, temperature profile and experimental verification
H. Ki, P.S. Mohanty and J. Mazumder*
Metallurgical and Materials Transactions A, 33A, num. 6, pp. 1831-1842, (2002).
3. Modeling of laser keyhole welding – I. Mathematical modeling, numerical methodology and role of recoil pressure, multiple reflections, and free surface evolution
H. Ki, P.S. Mohanty and J. Mazumder*
Metallurgical and Materials Transactions A, 33A, num. 6, pp. 1817-1830, (2002).
4. Multiple reflection and its influence on keyhole evolution
H. Ki, P.S. Mohanty and J. Mazumder*
Journal of Laser Applications, vol. 14, num. 1, pp.39-45, (2002).
Robert, I isn't familiar with these articles. But, I suspect, the same approach on the basis of evaporation hypothesis, as in other articles of the same authors is used in this article (H Ki, P S Mohanty and J Mazumder Modelling of high-density laser–material interaction using fast level set method. J. Phys. D: Appl. Phys. 34 (2001) 364–372).
Unfortunately, the hydrodynamic model associated with the evaporation hypothesis is usually used in the simulation of welding processes without experimental testing.
Instead the experimental verification of physical submodels used in these models, they are verified by the final results of the calculation. This is valid only in case if the physical submodel doesn't raise doubts.
But the legitimacy of application of evaporation hypothesis in modeling of welding process raises doubts as it has no experimental justification for conditions of welding and even contradicts many experimental data.
Many researchers note a great influence of thermocapillary mechanism of melt removal in deep penetration welding. Thermocapillary mechanism allows to obtain a consistent picture of the hydrodynamic in laser welding and to describe adequately welding process without the conflict to experimental data.
Unfortunately, there is no published numerical models until now, based on the thermocapillary mechanism of seam formation in deep penetration welding.
Dear colleagues! Оne of the best specialists in evaporation materialsV. V. Semak from Pennsylvania State University published just now in RG the new research - Atomistic misconception of current model for condensed matter evaporation and new formulation.
Below is a short quotation from this article:
" Evaporation is perceived by general community of scientists, engineers and educators as well studied and it is commonly believed that accurate physical model is mostly completed. However, those who attempt practical application of the existing models find that accuracy of predictions is unacceptably low for any real-world application. This indicates that current understanding of seemingly trivial evaporation phenomenon is inadequate."
Article Atomistic misconception of current model for condensed matte...
Dear colleagues! 238 specialists for 4 months viewed this issue. But the experimental evidence supporting the melt removal during laser welding under the influence of vapor recoil pressure, had not appeared untill now. Such data does not exist?
@Rinat, is this paper of interest?
Comparison between Phase Field and ALE Methods to model the Keyhole Digging during Spot Laser Welding
V.Bruyere1, C. Touvrey1*, P.Namy2
1CEA DAM, Valduc, 21120 Is sur Tille
2SIMTEC, 8 rue Duployé, Grenoble, 38100 France
or this?
Keyhole Formation During Spot Laser Welding. Heat and Fluid Flow Modeling in a 2D Axisymmetric Configuration
Mickael Courtois*1, Muriel Carin2, Philippe Le Masson2 and Sadok Gaied1
1ArcelorMittal Global R&D Montataire France, 2LIMATB Université de Bretagne-Sud Lorient France
*Corresponding author: [email protected]
Dear Riant Seidgazov,
The geometrical shape of keyhole can be determinate by statistical experiments and based on the points on the fusion melt/unmelt (geometrical points with known temperature T solidus) and if you use some heat source points and put the condition that the energy of that points can generate the identical geometry of the keyhole you will get the multipoints heat source (by inverse engineering) usefully for establish the temperature and fluid flow on welded pool surface. If you want to establish the vaporization influence, you know the initial dates of the laser spot and using Kunsten layer condition you can make the corrections for Maragoni coeficient with the heat flow gradient and establish the new values for your conditions. Personal, in welding engineering process, the multipoints heat source is sufficient for heat and fluid flow needed. You may find that way in my papers on Researchgates and for influence of vaporization you must make your own work.
https://www.researchgate.net/publication/260629367_Modelling_the_heat_and_fluid_flow_in_the_welded_pool?ev=prf_pub
https://www.researchgate.net/publication/233402898_Modelling_the_transport_phenomenon_involved_in_the_fusion-welded?ev=prf_pub
https://www.researchgate.net/publication/230754188_Modelling_the_heat_and_fluid_flow_in_the_welded_pool_from_high_power_arc_sources?ev=prf_pub
https://www.researchgate.net/publication/233536029_Modelarea_numeric_a_fenomenelor_de_transport_care_guverneaz_formarea_bii_metalice_la_sudura_prin_topire?ev=prf_pub
I believe that the bibliography can help you and i believe that some results are in my database.
Kind regards and success
Ioan Sorin Leoveanu
Data Modelling the heat and fluid flow in the welded pool
Conference Paper Modelling the transport phenomenon involved in the fusion-welded
Article Modelling the Heat and Fluid Flow in the Welded Pool from Hi...
Article Modelarea numerică a fenomenelor de transport care guverneaz...
Answer to Robert.
Robert, the hydrodynamic submodels of melt displacement by the recoil pressure of vapors are used in those articles. Unfortunately, the thermocapillary mechanism of melt removal is even not mentioned. This allows authors to avoid having to justify the choice of hydrodynamic submodels. And that is disappointing to me.
Ioan, I am interested in the physical mechanism of melt removal from beam impact zone. I see this as the key to understanding the fluid dynamics of pore formation in welding and weld quality prediction. One of my publications is devoted to this issue.
Of course, any model contains simplification. If our knowledge of the physics process is behind the needs of technology , the engineering modeling techniques are applied that you mention. But engineering methods may not completely replace physical simulation as a good prosthesis cannot be better healthy body. Therefore, it is impossible to abandon the improving the physical representations of the welding process.
Actual problems of application of evaporative approach in the engineering tasks are well represented in the publication V. Semak “Atomistic misconception of current model for condensed matter evaporation and new formulation.” One more quotation from this article:
“History of science and technology shows that significant and rapid progress can be achieved in particular disciplines leaving unanswered deeper questions about fundamental nature of the universe. However, at certain stage of such “modular” development the further progress becomes impossible without re-examining these multiple fundamental questions left behind.”
In my articles I verify the capillary mechanism of melt removal in welding and I intending to publish several articles on the subject.
There are some thoughts on a given topic in attached file
Conference Paper Verification of the melt displacement mechanism in deep pene...
I suggest to get acquainted with the discussion of the topic here
https://www.researchgate.net/post/Why_does_the_depth_of_laser_weld_increases_in_a_vacuum
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