Structural Analysis: Refining Project 1 Design

1. The CAD-to-SIM Iterative Loop

In a traditional design environment, moving from analysis results back to design changes can be a cumbersome process. It often involves exporting models, importing them into separate FEA software, and then manually re-doing the setup after every design tweak.

One of the most significant advantages of Onshape is how it streamlines this workflow. Because the CAD and simulation tools are part of the same platform, the process of refining your design becomes incredibly fast and intuitive. You can simply:

1. Analyze the design in the assembly tab.
2. Identify a problem area (e.g., low Factor of Safety).
3. Switch to the Part Studio tab and make a geometric change.
4. Switch back to the assembly tab. Onshape automatically detects the change.
5. Re-run the simulation to see the effect of your change in seconds.

This tight integration enables a rapid, iterative approach to design optimization.

2. Common Strategies for Design Refinement

So, you've found a problem area in your design. What do you do about it? While every problem is unique, most solutions fall into a few common categories. Let's explore the most fundamental strategies.

Strategy 1: Change the Material

This is often the simplest change to implement. If your part is failing with Aluminum 6061, will it work with Steel 1020? In Onshape, this is as easy as editing the material property in the Part Studio.

• Pros: Very fast to evaluate.
• Cons: Can have significant cost, weight, and manufacturing implications. A stronger material might solve the stress problem but make the product too heavy or expensive.

Strategy 2: Add Thickness

Another straightforward approach is to make the part thicker in the high-stress region. A thicker cross-section reduces stress and deflection.

• Pros: Easy to implement in CAD.
• Cons: An inefficient way to add stiffness. It increases material usage, cost, and weight, often more than necessary.

Strategy 3: Add Ribs to Improve Stiffness

A much more efficient way to strengthen a part is by adding ribs. Instead of adding mass everywhere (by increasing thickness), you strategically add material where it will have the most structural benefit. Your background in solid mechanics will tell you that stiffness is highly dependent on the area moment of inertia, which ribs are designed to increase.

While often associated with injection-molded plastics, the principle of using ribs for stiffening is universal and applies to machined and cast metal parts as well.

To design effective ribs, you need to consider more than just their location. Their geometry is critical for both structural performance and manufacturability.

The key takeaways for rib design are:

• Orient ribs parallel to the primary bending direction for maximum effect.
• Use multiple, smaller ribs rather than one massive rib for better stability and efficiency.
• Always include fillets at the base of your ribs to prevent creating new stress concentrations.

3. Your Turn: Refining a Project 1 Component

Now it's time to apply these concepts. For this exercise, let's focus on one of the structural components from your linear motion system project, for example, a motor mounting bracket or a guide rail support.

1. Open Project 1: Navigate to your Onshape document for Project 1.
2. Review Your Analysis: Open the assembly where you performed the FEA in the last lesson. Look at the Factor of Safety plot. Identify the area with the lowest FoS or an area with unacceptable deflection.
3. Formulate a Hypothesis: Based on the strategies above, how could you improve this area? Is it a sharp corner that needs a fillet? Is it a thin section that could be thickened or, better yet, reinforced with a rib?
4. Implement the Change:
   • Navigate to the Part Studio for the component you want to change.
   • Make the modification. Add a fillet, use the Extrude command to add a rib, or increase the thickness of a feature. Remember the design guides for ribs: aim for a rib thickness of about 50-60% of the main wall thickness and add generous fillets at the base.
5. Re-run and Compare:
   • Go back to your assembly tab. You should see a yellow icon or notification on the simulation results, indicating they are out of date.
   • Click to show the results again. Onshape will re-run the simulation with the updated geometry.
   • Compare the new Factor of Safety and Displacement plots to your original results. Did your change have the intended effect? Is the FoS now acceptable?

This cycle is the essence of simulation-driven design. By making small, informed changes and quickly checking their impact, you can efficiently converge on a robust and optimized design.

Conclusion

You have now completed the full engineering loop: from initial concept, to analysis, to interpretation, and finally to refinement. You've learned how to leverage Onshape's integrated environment to rapidly iterate on your designs and have explored fundamental strategies for improving the structural performance of a part.

Key Takeaways:

• The iterative design loop (Analyze -> Refine -> Re-analyze) is fundamental to engineering and is made highly efficient by Onshape's integrated platform.
• Common refinement strategies include changing materials, increasing thickness, and adding geometric features like ribs and fillets.
• Adding ribs is an efficient method to increase stiffness without adding excessive weight or material.
• Proper rib design, including orientation and filleting, is crucial to avoid creating new problems like stress concentrations.

Preview of the Next Lesson:
You've just improved your design based on FEA results. But in a professional setting, especially for a critical part, how do you build confidence that the simulation is giving you the right answer? In the next lesson, "Validate a design change by comparing hand calculations with FEA results," we will add another layer of engineering rigor. You'll use your foundational engineering skills to perform a "back-of-the-envelope" calculation to verify that your FEA results are in the right ballpark, a critical cross-checking step in any serious analysis work.