An Autodesk Inventor add-in that turns a hopper configuration into a verified release package

Problem

Every plate shop that makes hoppers redraws the same development for each new size. A rectangular inlet transitions to a smaller — sometimes offset — rectangular outlet through four converging sheet-metal panels. Each panel has to be developed flat, its bends and flange found and its bolt holes laid out; then the model, the drawings, the cut files and the bill of materials all have to agree. It is a half-day of careful, repetitive work per order, and the rules for it usually live in one senior designer's head and a spreadsheet.

The demonstration goal: show that the whole chain — from a configuration to a checked, releasable package — can be written once as tested software, with every rule identified and every output verified before it is allowed out.

Constraints

• The rules live in plain C#, outside the CAD system, so the same logic is tested without Inventor open and can be reused elsewhere.
• A second, independent implementation in Python re-derives the same rules from the specification and must agree.
• Every rule carries an identifier; the output is deterministic; nothing is produced or checked by a machine-learning model.
• Each job is a portable, self-contained folder — its own models, drawings, cut files, bill of materials, validation report and manifest.
• The release is fail-closed: it is refused unless every error-level check passes, and a refused release writes nothing.
• Drawings and cut files are demonstration documentation, not approved for fabrication.

Engineering logic

64 engine rules across eight families — validation, geometry, sheet metal, bolting, stiffeners, angle frame, mass and naming — plus 5 drawing rules, each with an identifier and a formula, labelled as a standard formula or a demonstration rule, and exercised by golden-configuration, failure-case and fuzz tests. The valley angle that governs flow is GEO-008; the choice between a formed flange and a bolted angle frame comes from the press-brake limit and a minimum wall angle (SM-006, SM-008); the bend allowance uses a stated K-factor (SM-005). Demonstration design rules are labelled as such and kept separate from standard formulas, so a client's own rules can replace them one identifier at a time.

System

A pure C# rule engine — with no Inventor dependency — turns eleven inputs into a full derived design. The add-in then drives Autodesk Inventor to build it: one sheet-metal panel per face, an assembly of four grounded panels placed by computed transforms, a general-arrangement drawing and one flat-pattern sheet per panel, four flat DXF, five PDF, and the bill-of-materials, cut-list and blanks CSVs. A ribbon command opens a configuration window; the operator sees eleven plain inputs, never a CAD parameter name, and drives Configure → Validate → Generate → Release.

Validation

The point of the system is not that Inventor produced files — it is that two independent routes agree the files are right, and nothing ships until they do.

Timings are measured on the development workstation with Inventor 2026.3, warm, three reps:

Result

• 64 engine rules across eight families; a second implementation in Python agreeing with the C# engine on all seven reference configurations.
• 111 automated tests passing — 15 core, 84 product and rule-engine, 9 live-CAD integration and 3 end-to-end — plus the independent cross-check.
• Flat patterns read back by ezdxf within the 2.5% validation gate — about 1.2% on the published nominal hopper, and exactly for plain panels; the live-CAD integration tests confirm the flat bend angles equal the computed face angles.
• A complete package — models, assembly, five drawings, four DXF, five PDF, the CSVs, a validation report and a SHA-256 manifest — produced in about five seconds warm; validation about half a second; the fail-closed release about a tenth of a second.
• Every sheet placed by a deterministic layout with its own collision checks, so a public drawing reads as controlled documentation rather than dropped views; the offset-outlet case reads correctly on both the plan view and the flat pattern.

What is not claimed: that any part has been fabricated from these files, or that the drawings are approved for production. They are demonstration documentation; the shop verifies before anything is cut, and the disclaimer says so.