CAD Automation August 1, 2026 8 min read 1824 reads Updated October 7, 2026 392 words

SolidWorks Automation: Batch Custom Properties, Cut-Lists, and Production Drawings

How to build robust C# and VBA automation tools for SolidWorks assemblies to eliminate manual metadata entry, sync weldment cut-lists, and auto-export drawing packages.

Md Anamul Hasan

Mechanical Design Engineer & CAD Automation Specialist

The High Cost of Manual CAD Administration

In mechanical engineering design offices, engineers spend up to 25% of their working hours on administrative CAD tasks rather than geometry modeling:

Manually opening hundreds of component files to verify part numbers and descriptions.
Synchronizing weldment structural member cut-lists with ERP purchase descriptions.
Printing drawing packages and exporting 1:1 DXFs for laser cutting.

By architecting direct automation via the SolidWorks Document Manager API and the SolidWorks COM API, we can reduce repetitive drawing package preparation from days to minutes.

1. Document Manager API vs. Full CAD Session Automation

When developing CAD automation, choosing the right API boundary is critical:

Requirement	SolidWorks COM API	Document Manager API
Execution Mode	Requires active SolidWorks license & GUI/background process	Headless, standalone executable (no SolidWorks install needed)
Speed	2–5 seconds per file open/save cycle	~50 milliseconds per file
Geometry Changes	Full feature tree access, rebuilds, drawings	Metadata only (Custom properties, configurations, BOM tables)
Ideal Use Case	Automated DXF export, model regeneration	Fast batch property sync, BOM auditing before ERP import

2. Batch Custom Property Synchronization Pattern

Below is a robust C# pattern for opening a SolidWorks part in silent batch mode, reading custom properties, and enforcing drawing block consistency:

using SolidWorks.Interop.sldworks;
using SolidWorks.Interop.swconst;
using System;

public class SolidWorksBatchSync
{
    private SldWorks _swApp;

    public SolidWorksBatchSync(SldWorks app)
    {
        _swApp = app;
    }

    public void UpdateComponentMetadata(string partPath, string partNumber, string material)
    {
        int errors = 0;
        int warnings = 0;

        ModelDoc2 doc = _swApp.OpenDoc6(
            partPath,
            (int)swDocumentTypes_e.swDocPART,
            (int)swOpenDocOptions_e.swOpenDocOptions_Silent,
            "",
            ref errors,
            ref warnings
        );

        if (doc == null)
            throw new Exception($"Failed to open document: {partPath}. Error code: {errors}");

        CustomPropertyManager propMgr = doc.Extension.get_CustomPropertyManager("");
        propMgr.Add3("PartNumber", (int)swCustomInfoType_e.swCustomInfoText, partNumber, (int)swCustomPropertyAddOption_e.swCustomPropertyReplaceValue);
        propMgr.Add3("Material", (int)swCustomInfoType_e.swCustomInfoText, material, (int)swCustomPropertyAddOption_e.swCustomPropertyReplaceValue);
        propMgr.Add3("VerifiedDate", (int)swCustomInfoType_e.swCustomInfoText, DateTime.UtcNow.ToString("yyyy-MM-dd"), (int)swCustomPropertyAddOption_e.swCustomPropertyReplaceValue);

        doc.Save3((int)swSaveAsOptions_e.swSaveAsOptions_Silent, ref errors, ref warnings);
        _swApp.CloseDoc(partPath);
    }
}

3. Weldment Cut-Lists and Automatic DXF Flattening

For sheet metal and structural frames, custom property automation must extend to cut-list item properties. Automating cut-list quantity rollups eliminates manual ordering mistakes on structural tubing, angle iron, and plate stock.