How to Unfold Sheet Metal Parts and Export to CAM in BricsCAD Mechanical

Quick answer: This uses SMUNFOLD. Manufacturing a sheet metal part requires a flat pattern with bend annotations, used in a CAM system to program CNC machines like laser cutters and press brakes; this flattening operation is called unfolding.

Unfolding a Sheet Metal Body

SMUNFOLD automatically creates a solid body corresponding to the flat metal sheet needed to manufacture the part through bending. This sheet places on the XY-plane, oriented along the coordinate axes similarly to the original body’s 3D orientation. To flip the unfolding’s orientation along the Z-axis, run SMUNFOLD again and select the opposite face of the original body.

Form Feature Unfolding Modes

Form features unfold according to the Unfolding Mode setting in the Mechanical Browser, confirming and expanding the Form feature unfolding mode property covered on this hub’s Global and Feature Properties page:

• Keep (0): keeps the form feature’s geometry on the unfolded representation.
• Remove (1): removes the form feature’s geometry from the unfolded representation.
• Project (2): generates a form feature symbol by projecting its edges onto the flange plane.
• Contour (3): generates a form feature symbol by projecting its external contour and holes onto the flange plane.
• Symbol (4): creates the unfold symbol on the UNFOLD_SYMBOL_UP or UNFOLD_SYMBOL_DOWN layer, depending on the form feature’s direction.

Set this per part in the Mechanical Browser.

Analytical Unfolding of Lofted Bends

Lofted bends on cylindrical and conical surfaces can unfold analytically, giving the unfolded shape and dimensions as if its middle surface were mathematically unrolled onto a plane. The same effect is achievable with a significantly increased number of samples instead. Set the Unfolding mode individually for each lofted bend feature; when analytical unfolding is possible, it appears as an option in the dropdown list.

Unfolding Procedure

1. Launch SMUNFOLD; you’re prompted to select a flange or lofted bend face to start unfolding, or choose Associative.
2. Select a face on the sheet metal part; you’re prompted to select a position for the unfolded body.
3. Specify a point; you’re prompted to validate the unfolded body and choose save 2D geometry, save 3D geometry, Optimize bend annotations, or Keep (the default).
4. Choose one: save the unfolded 3D solid as a separate drawing file; convert it to a 2D drawing file (.DWG or .DXF); rearrange the bend annotations; or keep the block with the unfolded part inside the sheet metal part’s own model.

Material Deformation

SMUNFOLD accounts for how sheet metal material deforms during bending. Bending a flat sheet with a tool like a press brake plastically deforms it, compressing the material on the inside of the bend and stretching it on the outside, so the part’s length measured along its surface differs between its flat and bent states. BricsCAD automatically computes the correct unfolded length based on the material’s deformation properties, defined either by setting the K-Factor parameter, or by attaching a Bend Table, confirming exactly both concepts covered on this hub’s dedicated K-factor and Bend Table pages.

Managing Layer Properties of the 2D Geometry

The 2D geometry generated by SMUNFOLD, SMEXPORT2D, and SMASSEMBLYEXPORT uses different colors for contours, bend lines up, bend lines down, overall dimensions, form features up, form features down, bend annotations, and attributes. Set these colors in the Sheet Metal / Commands / Layers for unfolding settings group of the Settings dialog, each entity type sits on its own dedicated layer, with color controlled by a corresponding user preference.

If a form feature’s 2D geometry came from a library component, its appearance is controlled by that component’s own properties at the moment of insertion. For the Project and Contour unfolding modes, where 2D geometry generates automatically from the 3D geometry instead, appearance is controlled by the Form Features Up Layer and Form Features Down Layer settings groups.

Exporting to CAM

Sheet metal parts created or edited in BricsCAD can be processed by different CAM systems (JETCAM or CADMAN-B, for example) to generate NC code for cutting and bending machines. A user preference controls SMUNFOLD‘s save 2D geometry option, customizing the resulting .DXF file for compatibility with popular CAM systems. SMEXPORT2D exports a sheet metal body’s unfolded representation as a 2D profile in .DXF or .DWG format; SMEXPORTOSM exports a sheet metal solid to the .OSM (Open Sheet Metal) format, native to the CADMAN-B CAM system.

Exporting an Assembly with Sheet Metal Parts to DXF

SMASSEMBLYEXPORT searches the assembly tree for sheet metal designs and exports them to .DXF, producing a set of files sorted by thickness into different subfolders within the output folder, along with an HTML report to review the results. Most sheet metal parts process automatically; poorly designed ones get flagged in that report for manual rework instead.

Frequently Asked Questions

How do I flip which side of the part the unfolded sheet is oriented toward? Run SMUNFOLD again and select the opposite face of the original body.

Can a lofted bend on a cylindrical surface unfold with perfect analytical accuracy? Yes, cylindrical and conical lofted bends can unfold analytically, matching what you’d get by mathematically unrolling the middle surface onto a plane.

What are the two ways to define a part’s material deformation properties for unfolding? Setting the K-Factor parameter, or attaching a Bend Table for greater precision.

What happens to poorly designed sheet metal parts when running SMASSEMBLYEXPORT on a whole assembly? They’re flagged in the generated HTML report for manual rework, rather than being processed automatically like well-designed parts.