DigiKey - Introduction to FreeCAD Part 10: Finite Element Method (FEM) WorkBench Tutorial | DigiKey
The creator found that off-the-shelf enclosures were too small for a specific printer, so they designed a custom frame using 1010 extruded aluminum. They realized that the metal corner brackets were more expensive than the extrusions and decided to 3D print them instead. To ensure the brackets could hold the necessary weight, they used FreeCAD's finite element analysis (FEA) to estimate deformation and stress. The process involves creating a mesh of the part, assigning materials, and setting constraints and loads. The analysis showed that the initial design could deflect significantly under load, indicating potential failure. By adding material to the design, they reduced deflection and stress, improving the part's strength. The video emphasizes the importance of using FEA to predict potential failure points in mechanical designs and suggests experimenting with different designs to optimize strength and reduce stress.
Key Points:
- Use FreeCAD's FEA to test 3D printed parts for stress and deformation.
- 3D print brackets to reduce costs compared to metal brackets.
- Create a mesh and assign materials in FreeCAD for accurate analysis.
- Adjust design to reduce deflection and stress, improving part strength.
- Experiment with different designs to optimize mechanical components.
Details:
1. 🔧 Designing a Custom Enclosure
- The need for a custom enclosure arose because off-the-shelf options were too small for the LOLs bot printer.
- A frame was constructed using 1010 extruded aluminum, chosen for its cost-effectiveness compared to pre-made enclosures.
- Connecting hardware costs, especially corner brackets, were significant, exceeding the cost of the aluminum itself.
- To mitigate costs, 3D printed brackets were used to hold panels, proving more economical than metal alternatives.
- Mechanical engineers utilized the finite element method (FEM) to calculate stress and deformation, essential for ensuring the enclosure's structural integrity.
- Finite element analysis (FEA) allowed for estimating stresses, heat transfer, and other factors, providing a comprehensive understanding of the design's performance under various conditions.
- FreeCAD's FEM workbench was employed for static analysis of bracket designs, demonstrating the approachability of advanced analysis techniques for custom projects.
2. 🛠️ Setting Up the Sketch and Constraints
- Change the document units to US customary to accommodate design measurements in inches, ensuring compatibility with standard parts.
- Create a symmetrical sketch on the XY plane with a square and circle centered on the origin to ensure balance and accuracy.
- Set both the length and width of the square to 1 inch to establish a fully constrained and standard design.
- Set the circle diameter to 0.266 inches, suitable for a 1/4-20 bolt, ensuring a loose fit for practical assembly.
- Pad the design to 0.8 inches thick, converting from the typical 2 mm standard to ensure structural integrity.
- Utilize external geometry from the original pad for creating a second sketch, maintaining connectivity with a concentric constraint for precise alignment.
- Ensure all geometric elements are constrained properly, removing any redundant constraints to optimize the design and prevent errors.
3. 🔍 Introducing FEM Workbench
- The FEM Workbench begins with importing a solid model created in the part design workbench, which is essential for initiating the analysis process.
- Users assign materials, constraints, and loads to the solid model within the FEM Workbench, which are critical steps in defining the problem's parameters.
- A third-party tool is utilized to convert the solid model into a mesh, a necessary step for enabling the solver to perform FEM analysis effectively.
- The analysis is conducted using a solver integrated with FreeCAD, specifically the external program Calculix, which handles the computation.
- Results of the analysis are presented in metric units, although the initial design can be in imperial units, indicating flexibility in unit systems.
- An analysis container organizes all components, including the body, results, and meshes, highlighting the non-linear but comprehensive workflow of the FEM Workbench.
- This system integrates seamlessly with external FEM programs, enhancing its capability and versatility for complex analyses.
4. 📐 Assigning Materials and Loads
4.1. Material Assignment
4.2. Load Constraints
5. 🔄 Creating Mesh for Analysis
- The boundary condition acts as a fixed constraint, akin to a bolt, providing stability and preventing movement.
- To apply a boundary condition, select the specific face and apply the fixed boundary condition, ensuring it remains immovable.
- The force load tool is used to apply the load, initially pointing in the wrong direction, requiring reversal to point downwards for accuracy.
- The load must be applied in Newtons, calculated as Force = Mass x Acceleration, ensuring precision in simulation.
- For a 5 kg mass under Earth's gravity (9.8 m/s²), the calculated force is approximately 49 Newtons, rounded to 50 Newtons for practical application.
- Reversing the load direction is crucial to simulate realistic conditions, as incorrect direction can lead to inaccurate results.
6. 🧪 Running the FEM Analysis
6.1. Mesh Creation
6.2. Mesh Optimization
7. 📊 Reviewing FEM Results
- Always regenerate the .inp file after any changes to the analysis setup, mesh, or constraints to ensure the solver operates on the most current data.
- Use static analysis when temperature gradients and vibrations are not significant factors in the model, as this simplifies the computational process.
- Verify the solver output for a 'done without error' message to confirm successful execution, and ensure no warnings or errors are present.
- After running the solver, hide the body and mesh to clearly view and interpret the results, focusing on specific outcomes such as stress distribution or deformation patterns.
- Pay attention to stress hotspots or unexpected deformations, which may indicate areas requiring design modification or further analysis.
8. 🔄 Modifying and Re-analyzing Design
- Analysis conducted using CCX and Pipeline CCX methods, which yield similar data for evaluating design modifications.
- Deflection observed at a displacement magnitude of up to 3.12 mm under a 5 kg load, indicating potential for material breakage.
- Von Mises stress analysis shows maximum stress of approximately 64 MPa and minimum of 11 kPa, assuming ductile material properties.
- 3D printing material properties, like PLA, are not isotropic, impacting stress distribution predictions.
- Observed maximum displacement is 3.5 mm, with stress reaching about 60 MPa, consistent with previous results.
9. 🔨 Strengthening the Design
- Material was added to the side of the object to strengthen it, specifically by creating a 2 mm pad or 0.08 inches, converted automatically to millimeters.
- A fully constrained sketch was created using external geometry with a triangle shape to add material to the design, ensuring precision and stability.
- The pad was mirrored using the YZ plane to ensure symmetry in the object design, enhancing structural balance.
10. 🔄 Updating the Analysis
10.1. Updating the Mesh
10.2. Rerunning the Solver
10.3. Rewriting the IMP File
11. 🧠 Interpreting Analysis Results
11.1. Displacement Findings
11.2. Stress Analysis Insights
12. 📘 Advanced Resources and Recommendations
- Utilize MIL-HDBK-5 for a comprehensive understanding of material load capacities in mechanical component analysis.
- Implement the FEM Workbench to optimize component design, aiming to reduce displacement and stress. Consider modifications like increasing the width or length of a bracket for improved performance.
13. 🎓 Final Thoughts and Learning Tips
- Basic building blocks for designing mechanical contraptions have been covered, providing a foundational understanding.
- The free cwiki is recommended as a comprehensive reference for various workbenches and tools within the program.
- Mango Jelly's YouTube channel is suggested for further skill enhancement, as it offers regular, valuable video content.
- Engaging with the FreeCAD forum is encouraged for troubleshooting and community support, highlighting the presence of helpful individuals.
14. 🎉 Conclusion and Encouragement
- Encourage sharing creations made in FreeCAD on social media platforms like X, Instagram, or LinkedIn.
- Use the hashtag #DKFreeCAD and tag Digi-Key to increase visibility of your work.
- Aim to build a community and showcase innovative work done using FreeCAD.