Discussion Closed This discussion was created more than 6 months ago and has been closed. To start a new discussion with a link back to this one, click here.

(Insanely) high temperatures in modeling Selective Laser Melting of 316L stainless steel

Please login with a confirmed email address before reporting spam

Hello everyone,

I would like to begin this thread by saying that (a) this forum is amazing as I have been learning so much in the last days and (b) I have just started using COMSOL and I am a noob at FEA in general, so please be merciful in your comments :)

That being said, I am trying to simulate laser melting of metals but, as a first simple approach, what I am interested in is to obtain a relatively accurate temperature distribution in the melt pool that forms when a laser scans over a slab of metal.

I started my model taking inspiration from the laser_heating_Si wafer tutorial that is available online: I created a parallelepiped of material (thickness x width x length) and a heat source with a gaussian profile. I am using heat transfer module with phase change, because I want to take into account the latent heat of melting of my material. I set the initial temperature of my slab to be room T (293 K) and I impose the same constant temperature to the sides and the bottom of the slab to be maintained throughout the simulation. For what concerns the top surface, there are both heat input from the laser (it scans along "length" direction at midpoint of '"width") and heat output due to the surface's emissivity.

When I run my model I obtain a nice melt pool that moves from one end to the other of the slab, the problem is that the size of this melt pool is quite small in terms of width and depth (given the parameters that I input and my knowledge of expected width and depth values from experimental data) and its peak temperature is INSANELY high.
For instance, in the case of a 55 µm laser spot size scanning at 100 W power and 2 m/s speed, I get peak temperatures as high as ~15000 K where, from common experiments, I should only be able to melt the alloy (T melting ~ 1673 K). We are talking about a discrepancy of 1 order of magnitude here.

Originally, I also experienced a singular issue where I observed local cooling below 293 K (even negative temperatures!) of the plate in front of the laser beam right before heating. I fixed this by refining the mesh (after reading it on the forum and making sure that the element size was smaller than the typical thermal diffusivity distance (x=sqrt(D*t)).
Although the negative temperature problem was fixed by mesh refinement, the peak temperatures remain in this crazy high region.

Given my poor familiarity with COMSOL, at the moment I am out of ideas on what the causes of this issue could be, mostly because it seems to me that my boundary and initial conditions make sense. Anyone who could shed some light on this will have my sincerest gratitude!

Bonus question: in some cases, when performing SLM of metals, the temperature of the molten metal can even reach and surpass the boiling point (~3200 K for steel) with subsequent vaporization (and relative latent heat). How could I model this into COMSOL? In other words, can I set the heat transfer module on my domain to have three distinct phases (solid-->liquid-->vapor) and thus model both the melting latent heat and the vaporizing latent heat?

Thank you in advance,
Umberto


6 Replies Last Post 29.11.2016, 14:16 GMT-5

Please login with a confirmed email address before reporting spam

Posted: 8 years ago 23.11.2016, 04:11 GMT-5
Hey Umberto,

I am working on pretty much on the same Problem. I am simulating heat transfer during selective lasermelting.

I managed to implement the phase change from solid to liquid and liquid to gaseous by defining an non linear temperatur dependant specific heat. Furthermore by defining a hysteresis you can implement a removal of gaseous material since it will be draged away by the cross Jet.

Sadly the results are similar to yours. The Peak temperaturs in the melt pool reach up to 15.000 K.
Have you found an explenation for this?

All the best

Micha
Hey Umberto, I am working on pretty much on the same Problem. I am simulating heat transfer during selective lasermelting. I managed to implement the phase change from solid to liquid and liquid to gaseous by defining an non linear temperatur dependant specific heat. Furthermore by defining a hysteresis you can implement a removal of gaseous material since it will be draged away by the cross Jet. Sadly the results are similar to yours. The Peak temperaturs in the melt pool reach up to 15.000 K. Have you found an explenation for this? All the best Micha

Please login with a confirmed email address before reporting spam

Posted: 8 years ago 23.11.2016, 10:18 GMT-5
Could you upload your model?
Could you upload your model?

Magnus Ringh COMSOL Employee

Please login with a confirmed email address before reporting spam

Posted: 8 years ago 24.11.2016, 09:50 GMT-5
Hi,

It's hard to say what a potential problem could be without access to the model. Perhaps some of the resources (papers, presentations, and a keynote talk) from the COMSOL website listed below could be of help. You could also contact the COMSOL support team.

Multiphysical Modelling of Keyhole Formation during Dissimilar Laser Welding (won a best paper award at the COMSOL Conference in Munich this year):
www.comsol.com/conference2016/download-paper/40041.pdf

Optimization of Welding Parameters using 3D Heat and Fluid Flow Modeling of Keyhole Laser Welding
www.comsol.com/paper/optimization-of-welding-parameters-using-3d-heat-and-fluid-flow-modeling-of-keyh-31831

Multiphysics Process Simulation of the Electromagnetic-Supported Laser Beam Welding
www.comsol.com/paper/multiphysics-process-simulation-of-the-electromagnetic-supported-laser-beam-weld-11122

Comparison Between Phase Field and ALE Methods to Model the Keyhole Digging During Spot Laser Welding
www.comsol.com/paper/comparison-between-phase-field-and-ale-methods-to-model-the-keyhole-digging-duri-15475

Keynote: Enhancing Welding Applications with Simulation:
www.comsol.com/video/keynote-enhancing-welding-applications-simulation

Best regards,
Magnus Ringh, COMSOL
Hi, It's hard to say what a potential problem could be without access to the model. Perhaps some of the resources (papers, presentations, and a keynote talk) from the COMSOL website listed below could be of help. You could also contact the COMSOL support team. Multiphysical Modelling of Keyhole Formation during Dissimilar Laser Welding (won a best paper award at the COMSOL Conference in Munich this year): https://www.comsol.com/conference2016/download-paper/40041.pdf Optimization of Welding Parameters using 3D Heat and Fluid Flow Modeling of Keyhole Laser Welding https://www.comsol.com/paper/optimization-of-welding-parameters-using-3d-heat-and-fluid-flow-modeling-of-keyh-31831 Multiphysics Process Simulation of the Electromagnetic-Supported Laser Beam Welding https://www.comsol.com/paper/multiphysics-process-simulation-of-the-electromagnetic-supported-laser-beam-weld-11122 Comparison Between Phase Field and ALE Methods to Model the Keyhole Digging During Spot Laser Welding https://www.comsol.com/paper/comparison-between-phase-field-and-ale-methods-to-model-the-keyhole-digging-duri-15475 Keynote: Enhancing Welding Applications with Simulation: https://www.comsol.com/video/keynote-enhancing-welding-applications-simulation Best regards, Magnus Ringh, COMSOL

Please login with a confirmed email address before reporting spam

Posted: 8 years ago 28.11.2016, 17:43 GMT-5
Hi all,

thank you for your replies to my original post! I apologize for the late reply but I have been busy with other stuff lately so I did not have enough time to work on COMSOL.
Also, I had to create a new account on this forum after my previous one was blocked when I first tried to upload the simulation file (some weird error about a non-authorized copy appeared). Anyway, the file should be attached to this message.

As you can see, it's a pretty simple model so far: at the moment I am using a 4340 steel that is available in the library but I intend to create my own material from scratch as soon as I have some time, including temperature-dependent properties and including latent heats by means of an effective heat capacity.
Anyway, if you run this simulation, you should find peak temperatures in the range of 12'000-13'000 K, while for the given parameters (100 W laser beam with 80 µm spot size, moving at 100 mm/s) it is commonly observed that the alloy just melts, and temperatures should not exceed 2-3000 K.
Even by modifying the thermal conditions at my domain boundaries did not change much: whether I force the parallelepiped faces to maintain their initial temperature of 293 K or whether I thermally insulate them, the crazy high temperatures in the melt pool don't seem to be affected: I guess that my domain is large enough.

I read with pleasure and much interest all the papers that Magnus attached and that just increased my frustration because I cannot seem to be able to even run a very simple model :(

Anyway, thanks in advance to whoever wants to take a look at this!
Hi all, thank you for your replies to my original post! I apologize for the late reply but I have been busy with other stuff lately so I did not have enough time to work on COMSOL. Also, I had to create a new account on this forum after my previous one was blocked when I first tried to upload the simulation file (some weird error about a non-authorized copy appeared). Anyway, the file should be attached to this message. As you can see, it's a pretty simple model so far: at the moment I am using a 4340 steel that is available in the library but I intend to create my own material from scratch as soon as I have some time, including temperature-dependent properties and including latent heats by means of an effective heat capacity. Anyway, if you run this simulation, you should find peak temperatures in the range of 12'000-13'000 K, while for the given parameters (100 W laser beam with 80 µm spot size, moving at 100 mm/s) it is commonly observed that the alloy just melts, and temperatures should not exceed 2-3000 K. Even by modifying the thermal conditions at my domain boundaries did not change much: whether I force the parallelepiped faces to maintain their initial temperature of 293 K or whether I thermally insulate them, the crazy high temperatures in the melt pool don't seem to be affected: I guess that my domain is large enough. I read with pleasure and much interest all the papers that Magnus attached and that just increased my frustration because I cannot seem to be able to even run a very simple model :( Anyway, thanks in advance to whoever wants to take a look at this!


Please login with a confirmed email address before reporting spam

Posted: 8 years ago 28.11.2016, 20:24 GMT-5
Hello,

You should use "Phase change material" node to include the latent heat of fusion and latent heat of vaporization.

From the manual:
"Phase Change Material
This node should be used to solve the heat equation after specifying the properties of a phase change material according to the apparent heat capacity formulation. This formulation gets its name from the fact that the latent heat is included as an additional term in the heat capacity. Up to five transitions in phase per material are supported."

-DW
Hello, You should use "Phase change material" node to include the latent heat of fusion and latent heat of vaporization. From the manual: "Phase Change Material This node should be used to solve the heat equation after specifying the properties of a phase change material according to the apparent heat capacity formulation. This formulation gets its name from the fact that the latent heat is included as an additional term in the heat capacity. Up to five transitions in phase per material are supported." -DW

Please login with a confirmed email address before reporting spam

Posted: 8 years ago 29.11.2016, 14:16 GMT-5
Hi DW,

thank you for your prompt reply. I am sorry but I cannot find anything like "Phase Change Material" in COMSOL.
The closest thing is going to Physics and then selecting a "Heat transfer with Phase Change": in this way I can include a phase transformation at a certain temperature with an associated latent heat. The problem is that there is only one phase change transformation allowed, from a phase 1 to a phase 2, so I would have to neglect either melting or vaporization.

Am I looking in the wrong place?
Hi DW, thank you for your prompt reply. I am sorry but I cannot find anything like "Phase Change Material" in COMSOL. The closest thing is going to Physics and then selecting a "Heat transfer with Phase Change": in this way I can include a phase transformation at a certain temperature with an associated latent heat. The problem is that there is only one phase change transformation allowed, from a phase 1 to a phase 2, so I would have to neglect either melting or vaporization. Am I looking in the wrong place?

Note that while COMSOL employees may participate in the discussion forum, COMSOL® software users who are on-subscription should submit their questions via the Support Center for a more comprehensive response from the Technical Support team.