Browser-Based FEA: Weight-Optimizing Real Structures

Guessing where to remove material wastes weight or breaks parts. Onshape Simulation brings cloud-native FEA into the same browser tab, so advanced teams optimize with evidence.

What it does. Onshape Simulation currently runs structural linear-static and modal analyses (it does not support fluid or thermal). Linear static returns stress, strain, and displacement — answering ‘will this part survive this load and how much does it deflect’. Modal returns natural frequencies and mode shapes — useful for long arms and elevators that can resonate under driving vibration.

Workflow on a structural plate.

1. Analyze the solid first. Run FEA on the finished solid before lightening, so you know the baseline.
2. Apply fixtures. Constrain the bolt holes that actually mount the part — over-constraining the FEA model gives falsely stiff results, the same anti-pattern as over-mating an assembly.
3. Apply realistic loads. Estimate the worst-case force: a gear reaction, an impact during a collision, or the weight of an arm at full extension times a dynamic factor. Apply a safety factor appropriate to impact-loaded structure.
4. Read the results. Stress contours show hot spots; displacement shows where it flexes. This tells you where it is safe to remove material, what thickness suffices, and which areas need reinforcement.
5. Lighten and re-run. Pocket the cool regions with Part Lighten, leave material in the hot load paths, and re-run. Iterate until the lightest design still sits comfortably below yield.

Worked example — an arm side plate. Baseline 0.190 in plate, fixed at four mounting bolts, loaded with the arm’s tip force at full extension. The first run typically shows stress concentrated in a narrow band between the pivot bore and the gearbox bolts — that is the load path. Lighten everywhere except that band; widen the rib if the hot-spot stress is near yield. The result removes mass while keeping peak stress within the safety factor.

Caveats. Linear static assumes small deflections and linear material; it is excellent for screening and comparative design but is not a substitute for physical testing of safety-critical or highly nonlinear parts. Use it to rank designs and guide pocketing, then validate the real part. Used this way, FEA turns the weight budget from guesswork into a measured tradeoff.

Key takeaways

• Onshape runs structural linear-static and modal FEA in-browser: stress/displacement for survival and deflection, modal for resonance (no fluid/thermal)
• Fix only real mount points, apply worst-case loads with a safety factor, and read the load path
• Lighten the cool regions, reinforce the hot load path, re-run, and validate critical parts physically — FEA screens, it doesn’t replace testing

This lesson was adapted from learnfrc.com.