What is the best kind of laser for melting the metal (specifically iron)?
I should say accuracy is very important.
The thickness of metal is about 50 micrometers.
Dear Amir! You say nothing about the melting mode you are going to operate with. But your wish to work with metal melting state gives me points that may be steady state melting without metal evaporation. Because your starting material is thin film for your task will be convinient and efficient to take the modern CW injection diode laser with power from 5 to 10 W in visual spectral range 405-700nm and focusing lenses to tune the melting process. All questions about thermal isolation of the melting phase for next manipulation are the on your own consideration. I believe that much tutorial exist about laser welding You can find to deep your knowledge for the subject.
Dear Amir
In order to ensure efficient melting of the selected metal sample, the laser pulse duration should correspond approximately to the thermal time constant of the sample. For your case, if we consider as a stainless steel material thickness of 50 microns, this time can be estimated from the relation:
t = l2/4a = 25∙10-6/4∙0,056 = 0,1∙10-3 s (a = 0,056 cm2/s – thermal diffusivity). At least the pulse width should not be less than the values obtained.
Equally important is the coefficient of reflection of the laser radiation on the metal surface, which depends on the wavelength and state of the surface. In the short-wavelength value (1 - R) is substantially higher than at the wavelength of CO2 laser. In particular, for stainless steel at a wavelength of 1.06 microns the quantity 1 - R ≈ 0,35. It is seven times higher than the in the case of CO2 laser.
Therefore, for your case, in my opinion, it is better to use a YAG laser (1.06) with a pulse width of not less than 0,1 ms (free-running mode).
In addition, YAG lasers are available, compact, easy to operate and reliable in operation. Element base for them is well established and can be easily replaced.
In more detail with the answer to your question can be found in:
«Industrial Applications of Lasers» ,
Author(s): John F. Ready
ISBN: 978-0-12-583961-7
Regards, Leonid
Energy W per pulse is easily estimated from the relation:
W∙(1-R) = cm (tm –t0) +rm,
Where c - specific heat capacity stainless steel, c ≈ 0.5 J / (g · K);
tm – melting point, r - specific heat of melting, r ≈ 84 kJ / kg,
m –mass of the melt (m ≈ ρ S∙l, ρ – density of metal ~ 8 g / cm3, S – laser spot area, l –thick of the sample)
Thank you everyone who gave their great answer to my question. i finished this project and used Fiber CW laser for my job. it is down now.
https://en.m.wikipedia.org/wiki/Selective_laser_melting
Selective laser melting (SLM), also known as direct metal laser sintering (DMLS) or laser powder bed fusion (LPBF), is a rapid prototyping
Direct metal laser melting (DMLM) is an additive manufacturing process that uses lasers to melt ultra-thin layers of metal powder to build a three-dimensional object. Objects are built directly from an .stl file generated from CAD (computer-aided design) data. The use of a laser to selectively melt thin layers of tiny particles yields objects exhibiting fine, dense and homogeneous characteristics.
The DMLM process begins with a roller spreading a thin layer of metal powder on the print bed. Next, an .stl file directs a laser to create a cross-section of the object by completely melting metal particles. The print bed is then lowered so the process can be repeated to create the next object layer. After all layers are printed, the excess unmelted powder is brushed, blown or blasted away. The object typically requires little, if any, finishing.
DMLM Vs. DMLS
The direct metal laser sintering (DMLS) process uses lasers to partially melt particles so they adhere to one another. The DMLM process is very similar, except that the material is completely melted to create ultra-thin liquid pools, which solidify as they cool.
The term “DMLS” is often used to refer to both processes, although the term “DMLM” is gradually emerging as the preferred way to reference the process when complete melting occurs.
https://www.ge.com/additive/additive-manufacturing/information/direct-metal-laser-melting-technology
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