Discussion Forum

Hello, I have a question how it would be possible in Comsol to model the convection & radiation which occurs on the top face of the last printed layer during the additive manufacturing process. Right now I've simulated the AM process where the elements are simultaneously thermally activated aswell as heated by following a pre-determined path of a heat source. For modelling the AM process I'm using the Heat transfer in Solids physics, combined with the Solid Mechanics physics for the activation expression used to activate the elements. Here it is no problem to model the convection & radiation which occurs on the side faces, since the general Heat flux and Surface-to-ambient Radiation functions can be used. However, I'm not really sure how to model the convection and radiation which occurs on the top face of the last printed layer when it is being printed. Is it not possible in Comsol to select the top face here since there is another domain on top (the layer above, which is being printed next). Here the convection & radiation should occur for only the total time it takes for a full layer to be printed (since after this another layer is deposited, and there is no convection and radiation for this layer anymore on the top surface).

Initially I tried to use the 'Boundary Heat Source' to model the convection and radiation on this top face (the face between the two layers), see the image below. This works fine, except the difficult part is making sure that the convection & radation stops exactly when the new layer is being deposited at that certain position. For this I've tried to use the prev function. Here the idea was that prev(solid.isactive,timeLayer) would give me the elements which are activated exactly one layer below the current position of the extruder, and thereafter set the convection & radiation of these elements to zero. However I don't think it possible to do this with the prev function, since the function didn't work when trying to recall previously activated elements.

My other suggestion was to model the convection & radiation for a certain amount of time when the element is being activated. For example, if it would take 20 seconds for a full layer to be printed. Here the convection & radiation on the top face should only occur for 20 seconds once an element is activated. However, until now I haven't been able to figure out a function which would make this possible in Comsol. Any idea's/thoughts how to model this would be very helpful. I've added an visual image below which should make the process more clear. In this image, the process of adding the third layer with according conditions is visualized.