In laser welding, how does the process affect absorption of power once the metal has melted? does it get absorbed 100% as when a keyhole forms, metal also evaporates.
I am getting the results if I use 100% absorption but I have not been able to confirm this from literature source. I have found a value of 84% for stainless steel but with this value I am not getting the required results.
Look also this review on page 239-240
Article Current issues and problems in laser welding of automotive a...
Those both are great publications, but take into account that they are based on CO2 laser welding and in latter case in Nd:YAG welding. If you use another laser type the keyhole behavior will be changed and absorption accordingly. Typically absorption is depending on power density, welding speed and wavelength. There is also always a fraction of laser power which will escape via root in case of full penetration..
I do agree with Davide. This is very good article, even it is missing the case of full penetration.
Just wondering what sort of results you are referring to? Are you trying to model the welding process using FE? Before you conclude that you get the right results using 100 efficiency, have you made sure that your other boundary conditions are accurate?
Respected Joseph, You are correct. I am trying to model welding using FE.
Yes im using the same boundary conditions as given in the paper, which are convection, radiaion and a predefined temperature field.
Have you compared the simulated and measured temperature history as well as weld pool geometry using the 100% efficiency?
We can never speak of 100% absorption. It will always be less than 100%, but it depends on each configuration what the value will be. Reasons why it can never be 100%
- In case of full penetration: A certain amount of the laser light (=energy) will pass through the keyhole & the meltpool. Not homogenuous thickness and not perfect fitting (in case of butt welding) will significantly increase the amount of laser light passing through and are considered loss for the weld process
- Wave length: Absorption depends on wave length. While solid state lasers and others with wave lengths of around 1000nm have significantly better absorption than CO2 lasers, it still not 100% perfectly absorbed which can be easily verified by still seeing a small plasma light (much smaller than with CO2)
- Back-reflected laser light from weld surface. Usually low amount, but can be up to a few % in extreme cases
Should you have in mind an energy balance based on weld parameters & weld geometry, please also consider
- Heat conduction between melt pool and heat affected zone, heating up the material next to the weld
- Gas ejection through keyhole process by evaporizing certain amounts in the weld (ex: Zn-coating, small amounts of iron)
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