Additive Manufacturing Simulation - Beat The Heat.
Updated: Mar 13, 2019
In Metal Additive Manufacturing (AM) a moving heat source continuously introduces heat to melt material in a layer-by-layer fashion. Over time, heat starts to accumulate in the solidified material and needs to be removed properly to avoid overheating which may lead to undesired mechanical properties or cause defects such as melt ball formation. Furthermore, high thermal gradients often introduce high localized stresses which subsequently lead to deformations.
Adequate thermal management is of great importance; process engineers address the potential thermal risks by changing machine parameters, placing support structures, changing part orientation and design features. This is done under consideration of enabling thermal flow from the heated layers into solidified regions, and eventually, into the building plate which serves as heat sink. However, for less experienced process engineers and complicated designs it is often hard to evaluate build configurations to ensure heat is not accumulated locally.
Similar to predicting deformations and stresses, simulation can also be used to provide feedback about the complex temperature evolution during the manufacturing process. Nevertheless, simulation presents some restrictions for simulating the thermal process. The actual AM process utilizes a heat source, e.g. a laser with dimensions in the micro scale range, to produce designs that are orders of magnitude larger than the laser dimensions. For Finite Element (FE) simulation this would require an enormously large mesh with a high level of detail and very long simulation times to properly simulate the localized melting process for entire designs.
The example pictures below show temperature plots of a laser introducing temperatures in a 2.5 x 2.5 square. A very fine tetrahedral mesh is used to properly simulate the temperatures of the melt pool and its peripheral regions.
In an industrial production environment, time-consuming simulations are not feasible; process engineers need quick feedback about critical regions that may suffer from high temperatures. One way to considerably reduce simulation times is via Multi-Layer or Multi-Volume approach.
The idea is to combine multiple, actual layers into a representative, macro-scale layer (=Multi-Layer/Multi-Volume) and consider the heat input (melting) for this entire layer rather than for each actual layer. To adjust this method for the simplification of multiple layers into one, the heat input must be corrected to match the actual process. This method is of course less accurate than simulating the individual trajectories for each layer, but this technique still gives great feedback about regions that suffer from heat removal, and is faster and better applicable in an industrial setting.
AdditiveLab software utilizes the Multi-layer method to allow the user to efficiently predict regions that suffer from localized and global overheating and may lead to undesired mechanical properties or defects such as melt ball formation. Due to the simplification of multiple actual layers into a representative volume, this method can produce realistic predictions within moments. Furthermore, AdditiveLab provides excellent visual feedback and allows to assess the thermal management of the build configuration.
The example below shows a Multi-layer simulation of two test geometries. The one to the left is attached to the base plate with solid material and the one to the right is attached via cone/cylinder supports. As you can see in the animation below, the left design initially accumulates higher temperatures near the building plate due to a higher volume that needs to be melted. As the build up progresses, the design to the right increasingly suffers from heat removal since the heat flow is more limited due to the cone/cylinder than in the left design.
The picture below shows the average temperature of the entire building simulation illustrating that the design to the right experiences the overall higher temperatures.