Laser Forming Process Tutorial in Abaqus

2.2. THEORETICAL AND BASE RELATIONS

The DFLUX subroutine is used to apply heat flux dependent on location and time in finite element simulation. For example, the linear heating processes of laser forming and welding (with a slight simplification) can be simulated by this subroutine. In the linear heating process, by applying heat flux to the surface of a sheet, a thermal gradient is created in its thickness. This thermal gradient causes permanent deformation of the sheet. To simulate this process, it is necessary to apply a time and location-dependent heat flux to the sheet. In this type of loading, a heat flux is applied on the plate, which is defined using the DFLUX subroutine, including the laser power, movement speed, beam diameter, absorption coefficient, and laser movement path according to the designed experiments.

The heat intensity of the laser beam on the sheet surface is modeled using an ideal Gaussian distribution, where the heat flux is described as follows:

Where q(r), is the required heat flux intensity on the surface of the material, η is the heat transfer efficiency, P is the power of the laser beam, R is the radius of the laser beam, r is the distance from the center of the laser beam, and (x₀, z₀) is the location of the beam.

If the laser head moves with speed V on the z-axis, we will have:

Figure 4: Flowchart of the modeling process of laser forming

In summary, the laser forming simulation procedure is as follows:

1. Thermal modeling of the laser forming Process

• Setting up the software environment and choosing Abaqus units
• Creating the part and partitioning it properly
• Defining the thermal properties of AISI 1010 and creating the relevant section
• Making an instance of the model in the Assembly module
• Creating two “Heat transfer” steps (laser movement and cooling steps), choosing the outputs
• Defining the interactions
• Applying the boundary conditions and load for the thermal section of the modeling
• Generating elements and assigning element types
• Calling the subroutine
• Submitting the job
• Viewing the results of the thermal modeling section

2. Preparing the subroutine
3. Mechanical modeling of the laser forming Process

• Defining the mechanical properties of AISI 1010 and creating the relevant section
• Creating two “Static, General” steps (laser movement and cooling steps), choosing the outputs
• Applying the boundary and initial conditions for the mechanical section of modeling (using the calling of output results of thermal modeling)
• Changing the type of elements (the type of elements should be adjusted according to the mechanical analysis.
• Submitting the new job
• Viewing the results of the mechanical modeling section

3. Workshop (Video file): A step-by-step guide on the laser forming simulation

In the workshop, we selected an AISI 1010 sheet under the heat flux caused by a laser beam. The workshop provides a full step-by-step guide through a video to simplify the simulation of the laser forming process.

In the video, we used two “Heat transfer” steps for thermal modeling and two “Static, General” steps for mechanical modeling and defined all the necessary outputs for the laser forming process. Then, the non-uniform mesh pattern will be used in such a way that very fine meshes will be employed near the scan path (due to the presence of high heat flux in this area) and coarser meshes will be employed in the regions far from the scan path. With this meshing pattern, we will achieve both demands of accurate results for simulation and reduction of computing time. Following this, we defined the thermal interactions between the sheet and the environment. Then we applied the boundary conditions and load, such as heat flux, initial temperature of the sheet, etc. Finally, we show how to call the subroutine, submit the job, and extract the results in full detail (for both thermal and mechanical modeling parts of the laser forming process).

To verify this model, the simulation results and experimental results of sheet deformation (U) are compared. The displacement of the sheet in the simulation is in good agreement with the experimental results.

It would be helpful to see Abaqus Documentation to understand how it would be hard to start an Abaqus simulation without any Abaqus tutorial.

One note, when you are simulating in Abaqus, be careful with the units of values you insert in Abaqus. Yes! Abaqus don’t have units but the values you enter must have consistent units. You can learn more about the system of units in Abaqus.