Submitting all three homework assignments will entitle you to a certificate of participation.
Homework 2 - Deadline: 10 July 2017
Generic DIY/Desktop 3D printers are able to print materials upto temperatures of around 280oC. The primary limitation of ramping the temperature higher would be electro-mechanical failure in parts of the 3D printer such as, plastic bending of the frame holding the extruder, failure of the stepper motor, etc. However, some modern 3D printers require bed temperatures as high as 140o C and filament temperatures as high as 380o C. High temperature materials such as PEEK, PEI and PPSU are being keenly looked into by the Aerospace industry due to their high abrasion resistance, high chemical resistance, low flame, self extinguishing, high strength character.
The additive manufacturing of these advanced materials is a major challenge with traditional open DIY 3D printers. NASA has looked into this, and arrived at the conclusion that the having an enclosed 3D printing area is very effective in improving the print quality. The detrimental effect of maintaining the enclosed volume in the 3D printer to a high temperature is mitigated through various measures such as using high temperature materials and integrating an onboard cooling system for the stepper motors.
Computational Fluid Dynamics(CFD) plays a important role in the design of such 3D printers. The high temperatures needed to maintain the print quality can be taken as a basis to analyse the average temperatures achievable in the 3D printer. A sub-domain of CFD, known as Convective Heat Transfer, prescribes the underlying core physics in the design process in a 3D printer. This tutorial is aimed at enabling the user to utilize SimScale’s Convective Heat Transfer utility in order to determine the average temperature inside the 3D printer with the hotbed temperature being a variable parameter.
This project can be used as a starting point for your simulation.
You would use this parametric CAD model at a further point in this tutorial.
Navigate to your geometry and click on New Mesh. We will be using the Hex-dominant parametric (only CFD) option for this homework. This approach provides a good user-control over the mesh. Please enter the number of cells in the x-, y- and z- directions as per the image below. This is done to have a uniform mesh in all directions.
The Background Mesh Box is the domain on which the calculations will be made. For internal simulation, it is defined in a manner such that the entire geometry is contained within it. The backgroundMeshBox is pre-defined by default. You can have a look here
The introduction of a Background Mesh Box splits the domain into two parts; inside the 3D Printer and outside the 3D printer. The material point decides the part of domain on which the calculations will be made. This tutorial aims at simulating the internal flow and heat transfer within the 3D Printer, hence the Material point can be placed anywhere inside the 3D-printer. We select our Material Point at the location: (0,0.1,0).
Now, we proceed to add another geometry primitive to our domain. Please select Geometry Primitives in the Navigation pane and click on New. Then select the option, Cylinder.
This Cylinder is intended for further mesh refinement in the region where the part is being 3D printed. The size and position of the Cylinder can be adjusted as per the required fidelity level of the simulation.
Mesh refinements are crucial to the convergence and accuracy of any CFD simulation. Next, we move onto mesh refinements by selecting Mesh Refinements in the Navigation pane and followed by clicking on New.
Please Note: After creating a new mesh refinement, select the Type and click on Save.
A Surface Refinement can be created for faces or solids. In both cases, the mesh will be refined near the surface of the selected object. Please implement a surface refinement as shown in the below image.
Feature Refinement allows you to create a finer mesh close to edges. It extracts the edges from the surfaces and refines the mesh as defined in the “Feature Refinement Levels” panel.
Region Refinement provides the option to refine your mesh in a pre-specified region. This region may be a solid body or a geometry primitive. We had previously defined a cylinder, which will now serve the purpose of region refinement. Please make sure that the Region refinement mode is set to inside. Select Cylinder from the Geometry Primitives as the region to be refined.
We add another surface refinement on the housing of the 3D printer.
You are now ready to begin the mesh generation. Please select Operation 1 from the Navigation pane and click on Start.
The mesh can now be visualized on the platform:
The more enthusiastic users can also qualitatively and quantitatively analyse the mesh in more detail with mesh clips and the meshing log, respectively.
Once the mesh is ready, we may assign the Topological entity sets A new topological entity set is assigned as follows:
- Navigate to topological entity sets in the Navigator
- Select the face entity from the viewer.
- Click on New from selection
- Name your entity set as you deem suitable and Create.
Please follow the above steps and these images to create the filament entity.
Please follow the above steps and this image to create the hotbed entity.
Please follow the above steps and this image to create the windows entity.
Please follow the above steps and this image to create the walls entity.
The mesh now been setup and satisfactorily analysed. The next step in your workflow is to move into the Simulation Designer. To create a new simulation, please click on New.
Please assign a name to your simulation and click Create.
Please select the Convective Heat Transfer analysis type and set the Boussinesq Approximation to off.
Proceeding to Domain selection, you can select the mesh on which you want the simulation to be performed. This is particularly productive when you would like to work with different meshes.
Since we are analysis the bouyant convection inside the 3D printer, a gravity model also needs to be set.
Navigate to Materials and and click on New. Next, add Air as the material from the Material Library.
Assign it to the volume in your mesh.
The initial conditions are assigned to the whole domain at the start of a simulation. During a simulation, the solver tries to converge the solution fields after taking these initial condition values as a starting point. Therefore, it is important to assign best guesses or analytical solutions as initial conditions when possible.
The overview of the physics setup is as follows:
You may now proceed to setup the boundary conditions of the simulation. To create a new boundary condition, please select Boundary Conditions in the Navigation plane and click on New.
The filament boundary condition can be created as follows:
To add new boundary conditions, you can right click on Boundary Conditions and Add boundary condition.
Please create a New Boundary Condition. The hotbed boundary condition can be created as follows:
Please create a New Boundary Condition. The windows boundary condition can be created as follows:
Please create a New Boundary Condition. The walls boundary condition can be created as follows:
The Numerics on the platform have been optimized and do not need to be changed for this simulation. You could analyse them by selecting Numerics in the Navigation pane :
The Simulation Control provides user-control over the simulation. You can increase the Number of computing cores to 16 and Maximum runtime to 30000s.
For accurate verification of the results, additional solution fields need to be post-processed. The platform provides a Result Control panel to serve this purpose. The additional Result Control Items (solution fields) can be setup and exported as follows.
Navigate to Result Control and click on New to add a Surface data item. Add the baseAverage monitor as follows:
Add the filamentHoldAverage monitor as follows:
You are now almost ready to start your simulation run. Please navigate to Simulation Runs in the Navigation pane and Check the simulation setup. If there is no error, please create a new run by clicking on New.
Please feed-in the name of your simulation and click on Start to begin your simulation run.
To create the proceeding simulations, you can simply duplicate the simulation setup by right clicking on the simulation you would like to duplicate and press Duplicate. Please feed-in the name of your new simulation and click on Save.
Setting up the parametric study
The modified design of the 3D printer has been appended with a a parametric X position of the extruder. The position would influence the heat distribution within the 3D printer. Your task is to modify the X-position in this range: ( -0.03 m, 0.03 m). An example to modify the X-position is as follows.
This is the geometry
Please make a copy as follows:
You can now see the parameter Xposition in the tree.Double Click on Xposition to modify the position of the extruder.
Subsequently, update the parameter within the provided range ( -0.03 m, 0.03 m).
Importing to the SimScale Platform:
Now, move back into your homework project on the SimScale platform. Navigate to Geometries and Import the model you created on Onshape:
Select the geometry in the pop-up window.
You now have your modified 3D printer on the platform.You may rename it as follows:
The Meshing and Simulation Setup procedure remains identical to the one described for the 5mm case.
Confirmation of Convergence:
It is a common misconception that residual convergence is equivalent to solution convergence. While residual convergence is imperative for a converged solution, it is also important to monitor the convergence of various fields at different locations in the domain.
To visualize the convergence plots, please navigate to the Post-Processor in the workflow and select *Convergence plot in the Navigator.
To visualize the pressure field convergence, select P_rgh under the filamentHoldAverage monitor.
To visualize the Temperature field convergence, select T under the filamentHoldAverage monitor.
To visualize the density convergence, select rho under the filamentHoldAverage monitor.
Duplicating the result:
To add a duplicate of the result, right click on Solution fields and select Load results to viewer.
Please make the second Run 1 invisible by clicking on the eye-symbol. This first Run 1 is the simulation run on which we will be performing the post-processing. Change the Opacity to 0.3
Slices provide planar representations of Solution fields. We use the slices to analyse the solution fields at different planar locations in the 3D printer.
To create a new filter, select the first Run 1 and click on Add filter.
Select Slice as the filter.
The Slice can be setup as follows:
The position of the plane can be varied with the tabs Origin and Normal. Please feel free to further analyse the solution fields by tweaking the slice.
To add a Glyph filter, please add a New Filter and select Glyph
The Glyph may be setup as follows:
The user is also free to analyse the results locally by downloading it to their system. An opensource post-processor, Paraview, can be downloaded here.
Thank you very much for your attention and Happy SimScaling!