Unfolding Shell Models

For designing design sheet metal models, some designers use solid modeling commands rather than sheet metal commands. Such models are made initially using solid modeling commands and then shell command is used to get uniform wall thickness and finally the model is converted into a sheet metal model. Such models when received by manufacturing vendors are often not suitable for unfolding. There are two reasons for this (i) unripped edges and (ii) sharp bends. To handle such cases, Sheet Metal Feature Recognition library (SMFR) provides options like (i) ripping and (ii) insert bends.

Model with an Unripped Edge and Sharp bends

For example consider the model shown in the figure above. Faces A and B are connected together, whereas to unfold the model, both these faces need to be unconnected. The unripped edge shown in the figure needs to be ripped. Sheet Metal Feature Recognition library provides an option to rip such edges in imported solid models. The edges to be ripped and the rip gap are to be provided for ripping. The imported model after ripping is shown below.

Model after Ripping

The model has two sharp bends with inner radius and outer radius as zero. For accurate unfolding and sheet metal bending, inner radius has to be specified. Sheet Metal Feature Recognition library provides an option to automatically convert such sharp bends into cylindrical bends. The sharp bend and the inner radius are to be specified for automatic conversion. SMFR can also detect sharp bends automatically for such conversion. The imported model after conversion of sharp bends into cylindrical bends and flat pattern obtained using SMFR are shown below.

Model after Conversion of Sharp Bends into Cylindrical BendsFlat Pattern

Unfolding imported models with flanges

Unfolding imported sheet metal models in CAD modelers always has limitations. Imported models having flanges as that shown in the figure below are not possible to unfold in most of the CAD modelers.

The latest version of Sheet Metal FR now has the capability to unfold imported models with such flanges. By enabling the patch stamps option, the above imported model can be unfolded with ease as shown below.

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Unfolding sheet metal models with stamp features

Unfolding sheet metal models with stamp features is handled in different ways by different modelers. Louver, dimple, bridge, lance and features that require forming are referred as stamp features in this context. For example, the model shown below contains few stamp features.

FR unfold has two options for unfolding.
(1) Unfold bend features : This option automatically recognizes all the bend features and unfolds only bends. All other features including stamp features remain as such as shown below.

(2) Unfold with patch stamps : This option automatically recognizes bends and stamps. Unfolding is performed by unfolding bends and patching stamps as shown below.

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Cutout Recognition and Unfolding in Sheet Metal

In sheet metal models, generally various types of cutouts are used. Even holes are special type of cutouts. There are different types of cutouts such as Internal cutouts, External cutouts, Multiface cutouts. Typical examples are shown in the figure below.

Internal cutouts are those which lie completely in a single plane. External cutouts are generally referred as notches and these cutouts lie along the boundary.


Multiface cutouts spread across multiple faces as shown in the figure below.


Sheet Metal FR identifies all these features and even gives flat patterns as shown below.