[Feature Idea] Cheapo topology optimization loop via parametric cuts + SolidWorks SimulationXpress #76

Motivation

When designing 3D-printed parts (e.g. PETG TV legs), the workflow today is:

1. Model in SolidWorks
2. Manually guess where to put lightening holes
3. Export STEP → FreeCAD + CalculiX → check Von Mises stress → iterate by hand
4. Import shapes into Solidworks and make an extrude-cut.

This should be automatable using tools already in this MCP server.

Proposed Feature: "Poor Man's Topo-Opt" via Surface Selection + SimulationXpress Optimize

Inspired by how topology optimization tutorials actually work in practice: run topo-opt → sketch around the surviving material → cut away the rest. This is a free-stack approximation of that loop using only tools already in this repo — no paid Simulation add-in required.

Phase 1 — Identify cut zones (geometry analysis, no FEA needed)

Instead of running a full topology solver, select candidate faces using two criteria:

• Large surface area — biggest wall panels have the most material to remove
• Perpendicular or parallel to the applied force vector — these faces carry the least bending stress; faces at ~45° to the load are shear-critical and skipped

# Pseudocode — maps to MCP tools
faces = analyze_geometry(part)   # get face list with normals + areas
force_vec = (0, 0, -1)           # gravity / load direction

candidates = [
    f for f in faces
    if dot(f.normal, force_vec) in [~0, ~1]   # perpendicular or parallel to load
    and f.area > min_panel_threshold           # large enough to be worth cutting
    and f.centroid_height > 0.30 * part_height # stay out of base stress zone
]

Phase 2 — Place parametric demo cuts

For each candidate face, add a single equilateral triangle cut (with corner fillets) driven by a SolidWorks global variable so all holes share one sweepable parameter:

• Global variable: hole_size = 15 mm ← the optimization target
• Fillet radius: max(hole_size * 0.10, 1.5 mm)
• Hole position: face centroid, upper 60–70% of panel height
• Orientation: point-up triangle (better compressive load path)
• Coverage cap: hole_size / panel_width ≤ 0.50

MCP call sequence: create_sketch() → add_polygon(sides=3) → add_fillet() → create_cut_extrude() → link dimension to hole_size global variable via set_dimension()

Phase 3 — SimulationXpress Step 6: Optimize

Once holes exist and are linked to hole_size:

1. Re-run SimulationXpress (fixtures + load already configured)
2. Step 6 → Optimize → Parameters → link the hole_size dimension
3. Sweep range: 5 mm → 40 mm, step 2.5 mm
4. Constraint: max Von Mises stress ≤ yield_Z / target_SF (e.g. 28 MPa ÷ 3 = 9.3 MPa for PETG)
5. SimulationXpress finds the largest hole_size that satisfies the constraint in a single pass — no manual re-run loop needed
6. Apply optimal value → rebuild → export STEP for slicer

Full loop sketch (updated)

load_part(path)

# Phase 1: geometry-based zone selection (no FEA required)
candidates = select_cut_faces(force_vec, min_area, no_cut_zone=0.30)

# Phase 2: place parametric cuts driven by global variable
for face in candidates:
    place_triangle_cut(face, global_var="hole_size", initial=15)
    check_constraints()         # min wall, coverage cap, fillet radius
    if constraints_violated:
        rollback_last_cut()

# Phase 3: let SimulationXpress sweep hole_size and find optimum
run_simulation_xpress()
result = optimize_dimension(
    var="hole_size",
    range=(5, 40), step=2.5,
    constraint=f"max_stress <= {yield_z / target_SF}"
)
apply_dimension(result.optimal_value)

output_report(mass_before, mass_after, sf_final, hole_size=result.optimal_value)

New MCP Tool: cheapo_topo (Lightweight Active-Model & Selection Inspection)

We also need a lightweight read-only tool for agent context gathering before modeling or simulation operations.

Purpose

Inspect the active SolidWorks model and any selected surfaces without triggering expensive simulations or rebuilds. Useful for:

• Understanding which faces are currently selected
• Getting basic topology summary (face/edge/body counts)
• Pointing agents to the right SolidWorks API help docs for Simulation workflows

Desired input shape

{
  "document_path": "C:\\path\\to\\part.SLDPRT",
  "selection_mode": "active_selection",
  "include_topology": true,
  "include_help_links": true,
  "max_faces": 25,
  "include_mass_properties": false
}

Desired output shape (success)

{
  "status": "success",
  "document": {
    "title": "part.SLDPRT",
    "path": "C:\\path\\to\\part.SLDPRT",
    "type": "Part",
    "configuration": "Default",
    "feature_count": 42
  },
  "selection": {
    "selected_count": 3,
    "selected_entities": [
      {
        "entity_id": "Face<12>",
        "type": "Face",
        "kind": "planar",
        "area_mm2": 1248.7,
        "normal": [0, 1, 0]
      },
      {
        "entity_id": "Face<18>",
        "type": "Face",
        "kind": "cylindrical",
        "area_mm2": 932.2,
        "normal": [0.7, 0.1, 0.7]
      }
    ]
  },
  "topology_summary": {
    "face_count": 28,
    "edge_count": 61,
    "body_count": 1,
    "shells": 2
  },
  "help_links": [
    {
      "label": "ICosmosWorks",
      "url": "https://help.solidworks.com/2026/english/api/swsimulationapi/SOLIDWORKS.Interop.cosworks~SOLIDWORKS.Interop.cosworks.ICosmosWorks.html"
    },
    {
      "label": "SolidWorks API Help Index",
      "url": "https://help.solidworks.com/2026/english/api/help_list.htm?id=11"
    }
  ],
  "execution_time": 0.23
}

Error output shape

{
  "status": "error",
  "message": "No active SolidWorks document or no valid selection set found.",
  "help_links": [
    {
      "label": "ICosmosWorks",
      "url": "https://help.solidworks.com/2026/english/api/swsimulationapi/SOLIDWORKS.Interop.cosworks~SOLIDWORKS.Interop.cosworks.ICosmosWorks.html"
    }
  ]
}

Design notes

• Intentionally cheap: no rebuild, no mesh generation, no simulation solve — read-only inspection only
• Good first pass: before more expensive modeling or simulation prep workflows
• Selection-aware: captures the current user's selected faces to help agents reason about where cuts or constraints should go
• Help link embedding: returns the official SolidWorks Simulation API docs + help index so agents can reference the correct COM interfaces

References

• ICosmosWorks (SolidWorks Simulation API)
• SolidWorks API Help Index

Parametric cuts via global variables / equations

Each cut is driven by SolidWorks global variables and equations (not hardcoded dimensions) so that:

• Hole size, spacing, and fillet radius are exposed as named parameters (e.g. "hole_size", "wall_clearance")
• The agent can sweep parameter values without rebuilding sketches from scratch
• Results are reproducible and human-editable after the run

Note: Full parametric variants / global variable / equation-driven curve tooling is already tracked in #23 (thanks @pedropaulovc). This feature depends on — or should be built on top of — those tools once they land.

Cut geometry constraints (FDM-safe defaults)

Implementation options

Option A — Free stack (full loop):

• SolidWorks MCP → export_step() → FreeCAD + CalculiX for initial stress map
• BESO or ToOptix for topology hint → use result to inform face selection in Phase 1
• SimulationXpress Step 6 for final hole-size optimization

Option B — Native SW only (no FreeCAD):

• Skip external FEA entirely; use face normal + area heuristic for Phase 1
• SolidWorks MCP → SimulationXpress COM automation for stress check + Step 6 optimize
• Simpler setup; limited to isotropic material model (no Z-axis anisotropy for FDM — use conservative PETG Z-yield as the constraint value to compensate)

Output

• Lightened .SLDPRT with named, parametric cut features (editable post-run)
• Report: original mass, final mass, % reduction, optimal hole_size, final safety factor
• Optional: STEP export of final part ready for slicer

Related issues

• Proposal: phased expansion of MCP tool surface (assembly mates, reference geometry, parametrics, BOM, measurement) #23 — parametric variants, global variables, equation-driven curves (dependency — Phase 2 and 3 require global variable read/write via MCP)
• feat(tools): integrate text-to-cad 'cad' skill as STEP-first generation branch (CAD tools → SolidWorks translator) #43 — text-to-CAD STEP-first generation (complementary)

Use case that motivated this

Designing PETG TV leg replacements for a Sharp Roku 55–65". FEA showed safety factor ~14–18× at 50 N load — massively overbuilt. Wanted to automate the "cut holes until SF drops to 3×" loop instead of doing it by hand.

/cc @pedropaulovc — the global variable / equation tools in #23 are a natural foundation for the hole_size sweep in Phase 3 here.