NLP-to-CAD Industrial Skill

Purpose

Convert natural language engineering descriptions into CAD models, drawings, and manufacturing data.

Execution Flow

Phase 1: Parse Intent

1. Extract technical entities: dimensions, materials, tolerances, features
2. Identify CAD operation type: create/modify/analyze/export
3. Determine target format and units
4. Map domain-specific terms to standard notation

Phase 2: Knowledge Retrieval

• Load relevant industry standards from references/industry-knowledge/
• Fetch applicable CAD templates from references/cad-templates/
• Match NLP patterns from references/nlp-patterns/

Phase 2.5: 联网检索 + 三步式推荐 (Pre-generation guidance)

When the user gives only a natural-language description without full dimensions
or structure, do not generate blindly. See references/nlp-patterns/web-search-and-recommend.md
(WebSearch / WebFetch 联网搜索 → 有参考图纸则采用 → 无则三步式推荐):
1. Search the web for the object's standard/typical features (dimensions, standards, materials, structure).
2. If a reference CAD drawing / standard spec is found → use it and record the source.
3. Otherwise → three-step recommendation (类型 → 关键尺寸 → 输出内容) via AskUserQuestion, one question per step.
4. Summarize the confirmed parameters before generating.

Phase 3: Code Generation

• Select appropriate code generator based on target CAD system (see "Supported CAD Systems" below — each entry points to its own reference under references/code-generators/. Always read the reference before writing code; the ZWCAD one in particular has multiple non-obvious pitfalls that will silently produce wrong output.)
• Apply parametric constraints and dimensions
• Generate manufacturing annotations

Phase 4: DXF + PNG 预览 (Preview rendering)

After the drawing is produced, always also deliver a raster preview so users without
CAD software can see the result. See references/code-generators/dxf-png-render.md:
- Generate/export the drawing as DXF (ezdxf, or $doc.SaveAs(...dxf) from ZWCAD).
- Render part.png from the DXF with ezdxf.addons.drawing + matplotlib (Agg backend, CJK font for Chinese labels).
- Deliver part.dxf + part.png together.

Phase 5: Validation

• Syntax check for output format
• Engineering rule validation (dimensions, tolerances, materials)
• Cross-reference with industry databases

Output Contracts

CAD Model Output

Format: STEP | IGES | STL | Parasolid | ACIS | Native CAD format
Units: mm | inch
Precision: 0.001mm standard
Validation: ISO 10303 compliance

Engineering Drawing Output

Formats: PDF | DWG | DXF | PNG (raster preview)
Views: orthographic | isometric | section | detail
Annotations: GD&T per ASME Y14.5-2018

Every DXF/DWG drawing ships with a matching PNG preview (see
references/code-generators/dxf-png-render.md), so the result is viewable
without CAD software installed.

Manufacturing Data Output

CNC: G-code | M-code
Reports: BOM | Process sheet | Material specs

Supported CAD Systems

• FreeCAD (Python API)
• OpenSCAD (CSG)
• Onshape | Fusion 360 (via API)
• STEP/IGES standard exchange
• ZWCAD / 中望 CAD (Windows COM via PowerShell) — see references/code-generators/zwcad-com.md. Use this when the target CAD is 中望 CAD Personal (Windows). Verified against ZWCAD 3.0.1 (COM Version 2025) on Windows 11 + PowerShell 5.1. Key constraint: Document.ActiveLayer setter is racy — always pass the layer explicitly and set entity.Layer after AddLine returns.

Error Handling

• Unclear dimension → ask for clarification with suggestions
• Invalid material → map to nearest standard grade
• Complex geometry → offer simplification or manual approach
• Unsupported format → suggest nearest equivalent
• ZWCAD-specific traps (see references/code-generators/zwcad-com.md §4 for the full list):
• Utility.CreatePoint does not exist — pass [double[]] @(x,y,z) directly.
• AddPolyline with flat double array throws 0x80210011 — use 4× AddLine for rectangles instead.
• ActiveLayer setter race — entities may land on the wrong layer. Always set entity.Layer explicitly after creation.
• SendCommand blocks on wizard-style commands (_PLOT, _EXPORT, _DIMLINEAR); use COM methods ($zw.ZoomExtents(), SetVariable) instead.
• Default txt.shx font renders CJK as garbage — create a CN text style with simsun.ttc and set ActiveTextStyle before AddText.
• PowerShell 5.1 parses .ps1 as ANSI — Chinese literals truncate. Use [char]0xXXXX form, or save script as UTF-8 BOM.

Example Triggers

• "设计一个法兰，直径200mm，厚度20mm，材料304不锈钢"
• "生成这个零件的工程图，标注尺寸和公差"
• "把这段描述转成STEP文件：圆柱形壳体，两端开口..."
• "创建BOM表，包含材料清单和数量"
• "这段管路设计的展开图，DN50的管道"

Integration

All heavy data lives in references/. Main file handles routing and orchestration.
Do not inline large tables, code samples, or domain knowledge—delegate to reference files.

Two new reference files drive the pre/post-generation UX:
- references/nlp-patterns/web-search-and-recommend.md — 联网检索该对象特征；有参考图纸则采用，无则三步式推荐（类型 → 尺寸 → 输出）后生成。
- references/code-generators/dxf-png-render.md — 纯 Python 生成 DXF 并渲染 PNG 预览，供无 CAD 用户查看。