About Heat Source Calibration

There are models available to define the heat source in the AM process and that are also available with the Heat Source Calibration Calculation Type: Gaussian, Double ellipsoidal, or Conical. All these heat sources rely on different sets of parameters to fully define the heat input to the powder and solid substrate.

The standard Gaussian heat source model (a Single Point Calculation Type) requires defining the Absorptivity and the Beam radius on the AM Calculator Configuration window. The keyhole model takes into account the effect of evaporation recoil pressure that produces a keyhole, if present for the given processing conditions. Multiple reflections are also included in the keyhole model to improve the calculation of the keyhole shape. The absorptivity of the liquid can be calculated but often requires correction due to uncertainty in the model, surface oxides, and so forth. The beam radius of the heat source of the printer is, however, most often known but does not always match the definition of the beam size for the Gaussian heat source used in the simulation. Leveraging the experimental melt pool data and the relation between melt pool size and energy density can help to calibrate the absorptivity and beam radius for the Gaussian heat source model.

The keyhole model is available for Gaussian, Core-ring, and Top-hat heat sources. See About the Keyhole Model for some additional information.

For information about using calculated or constant absorptivity with a Gaussian Heat Source Calibration, there is additional theory in About the Absorptivity Model. The associated settings for this type of calibration is in the subsection Heat Source Calibration.

Similarly, for volume heat sources, i.e. Double ellipsoidal and Conical, it is necessary to enter four and three parameters, respectively, along with the absorptivity. Since volume heat sources are a numerical way to correctly capture the shape of the melt pool, it is not always possible to know the values of these parameters for the processing conditions.

However, according to the literature [2021Gra] you can find a relationship between the size i.e., width and depth of the melt pool, and the energy density (defined as the ratio of power and scanning speed) and based on that, you can also find a relationship between the heat source parameters and the energy density.

See Additive Manufacturing Module Theory for a general overview including details about the heat sources.

This means that if a set of experimental data for an alloy can be provided in the form of power, scanning speed, width of the melt pool, and depth of the melt pool, then you can perform a heat source calibration to calibrate the heat source parameters for the given material. This is done by running an optimization algorithm for the selected experimental data and then choosing an appropriate function for each heat source parameter. As a result, the output includes expressions of the given parameters as a function of the energy density, which can be saved and is available later in heat source list as a Users heat source. This is for any given process parameter (i.e. the saved heat source can be used for any process parameter).

When a Users heat source option is available to choose in the heat source list, then only the Power of the heat source needs to be entered and the rest of the parameters, including the absorptivity, are automatically included in the simulation based on the selected expressions when originally saving the heat source calibration data.

In order to set up the calibration of the heat source, you select the Steady-state simulation type and then select Heat Source Calibration as the Calculation Type. The calibration is performed assuming steady-state conditions so most of the configurations are done in the same way as the Single Point Steady-state simulation. The difference is that you need to choose which heat source to use, i.e. Gaussian, Core-ring, Top-hat, Double ellipsoidal, or Conical.

For more details about including the Heat Source Calibration Calculation Type during the simulation set up, go to AM Calculator Conditions Settings. Then go to Visualizing Heat Source Calibrations for details about navigating the various previews and results.