Sheet Metal Features

Specialized feature extraction for sheet metal parts, including bends, corners, holes, reliefs, and deformation features.

Note

Prerequisites: Sheet Metal Shapes

Tip

Tutorial Data File: lances-sheet-metal.step

Sheet Metal Features

This guide covers the feature types and feature extraction for sheet metal parts. It focuses on identifying manufacturing features like bends, corners, holes, and deformations.

Prerequisite: First recognize the sheet metal structure using SheetMetalRecognizer (see Sheet Metal Recognition).

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Overview

After recognizing a sheet metal part, the SheetMetalFeatureExtractor analyzes thickness face chains to identify manufacturing features. Features are categorized into:

• Bending features: Bends, curls, hems

• Corner features: Sheet corners

• Cut features: Notches, holes (round, rectangular, slotted)

• Offset features: Jogs

• Relief features: Bend reliefs, corner reliefs

• Deformation features: Lances, louvres, embosses

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Quick Start

from volmdlr.model import VolumeModel
from volmdlr_tools.shapes.recognizers import SheetMetalRecognizer
from volmdlr_tools.features.extractors import SheetMetalFeatureExtractor

# Load and recognize sheet metal
volume_model = VolumeModel.from_step("data/step/lances-sheet-metal.step")
shape = volume_model.primitives[0]

recognizer = SheetMetalRecognizer(shape=shape)
if recognizer.perform():
    sheet_metal = recognizer.result

    # Extract features
    extractor = SheetMetalFeatureExtractor(sheet_metal=sheet_metal)
    extractor.perform()

    # Access features
    print(f"Boundary features: {len(extractor.boundary_features)}")
    print(f"Internal features: {len(extractor.internal_features)}")

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SheetMetalFeatureExtractor

The main class for extracting features from a recognized sheet metal part.

Constructor

SheetMetalFeatureExtractor(
    sheet_metal: SheetMetalShape,
    name: str = ""
)

Methods

• perform() -> bool: Execute feature extraction

Properties

Property	Type	Description
boundary_features	list[Feature]	Features on the boundary (perimeter)
internal_features	list[Feature]	Features inside the sheet (holes, etc.)

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Feature Types

Bending Features

Feature	Description	Detection Pattern
Bend	Simple bend (angle < 90°)	Single fan-shaped face pair, path distance = 1
Curl	Curved bend (angle > 90°)	Single fan-shaped face pair, path distance = 3
Hem	Hemmed edge (180° bend)	Single fan-shaped face pair, path distance = 5

Detection: Bends are identified by pairs of fan-shaped faces in the thickness face chain. A fan-shaped face has two concentric circular edges and represents a curved portion of the sheet.

# Access bends from boundary features
bends = [f for f in extractor.boundary_features
         if f.__class__.__name__ == 'Bend']

for bend in bends:
    print(f"Bend angle: {bend.angle}")

Corner Features

Feature	Description	Detection Pattern
Corner	Sheet metal corner	Convex angles (90°-180°) at boundary

Corners are identified at convex angle transitions in the boundary chain.

Cut Features

Feature	Description	Detection Pattern
Notch	Open-ended cut	Open chain, concave angles at boundary
Rectangular Hole	Rectangular cutout	Closed chain, 4-8 faces, 4 planar, 2 parallel pairs
Round Hole	Circular cutout	Closed chain with cylindrical face
Slotted Hole	Elongated cutout	Closed chain with two cylindrical faces

Cut features are identified from internal thickness face chains:

# Access internal features (holes, cutouts)
internal = extractor.internal_features

for feature in internal:
    feature_type = feature.__class__.__name__
    print(f"Internal feature: {feature_type}")

Offset Features

Feature	Description	Detection Pattern
Jog	Offset bend	Two fan-shaped face pairs, parallel sections

Jogs create a step in the sheet metal by combining two bends.

Relief Features

Feature	Description	Detection Pattern
Relief	Material relief	Open chain, 3 faces, at bend intersection
CornerRelief	Corner cutout	Small relief at bend corner

Reliefs are cuts that allow proper bending without material interference.

Deformation Features

Feature	Description	Detection Pattern
Lance	Lance feature	Partial cut and bend
Louvre	Ventilation louvre	Multiple parallel lances
Emboss	Embossed shape	Local deformation
FlangedCutout	Cut with flange	Cut with bent edge

Deformations are recognized by the RegionDeformationExtractor (the default), which segments each side into panel and candidate regions, so embosses and flanged cutouts merged with cutout rims or the sheet boundary are found too:

from volmdlr_tools.features.extractors import RegionDeformationExtractor

deform_extractor = RegionDeformationExtractor(sheet_metal=sheet_metal)
deform_extractor.perform()

deformations = deform_extractor.result

The wire-seeded DeformationExtractor remains available with the same interface; it only finds deformations hanging on a face’s inner wire. Through the processor, pick the extractor with FeatureProcessor.extract_deformations(extractor_class=...).

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Complete Example

from volmdlr.model import VolumeModel
from volmdlr_tools.shapes.recognizers import SheetMetalRecognizer
from volmdlr_tools.features.extractors import SheetMetalFeatureExtractor
from volmdlr_tools.features.extractors import DeformationExtractor

# Load the sheet metal part
volume_model = VolumeModel.from_step("data/step/lances-sheet-metal.step")
shape = volume_model.primitives[0]

# Step 1: Recognize sheet metal structure
recognizer = SheetMetalRecognizer(shape=shape)

if not recognizer.perform():
    print("Not a valid sheet metal part")
    exit()

sheet_metal = recognizer.result
print(f"Sheet thickness: {sheet_metal.thickness:.3f}")

# Step 2: Extract sheet metal features
feature_extractor = SheetMetalFeatureExtractor(sheet_metal=sheet_metal)
feature_extractor.perform()

# Step 3: Print feature summary
print("\n=== Boundary Features ===")
for feature in feature_extractor.boundary_features:
    print(f"  - {feature.__class__.__name__}")

print("\n=== Internal Features ===")
for feature in feature_extractor.internal_features:
    print(f"  - {feature.__class__.__name__}")

# Step 4: Extract deformation features
deform_extractor = DeformationExtractor(sheet_metal=sheet_metal)
deform_extractor.perform()

print("\n=== Deformation Features ===")
for feature in deform_extractor.features:
    print(f"  - {feature.__class__.__name__}")

# Step 5: Visualize
boundary_shell = sheet_metal.get_boundary_thickness_shell()
boundary_shell.color = (1.0, 0.5, 0.0)  # Orange

internal_shells = sheet_metal.get_internal_thickness_shells()
for shell in internal_shells:
    shell.color = (0.0, 0.8, 0.2)  # Green

VolumeModel([shape, boundary_shell, *internal_shells]).babylonjs()

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Feature Categories

Features are organized into categories using the FeatureCategory enum:

Category	Features
BENDING	Bend, Curl, Hem
CORNER	Corner
CUT	Notch, RoundHole, RectangularHole, SlottedHole
OFFSET	Jog
RELIEF	Relief, CornerRelief
DEFORMATION	Lance, Louvre, Emboss, FlangedCutout

from volmdlr_tools.features.feature_types import FeatureCategory

# Filter by category
bending_features = [f for f in all_features
                    if f.category == FeatureCategory.BENDING]

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See Also

• Sheet Metal Recognition - Shape recognition with SheetMetalRecognizer

• Feature Recognition - General FeatureProcessor usage

Related API Documentation

• volmdlr_tools.features.extractors package - Feature extractors

• volmdlr_tools.features.feature_types.sheet_metal package - Sheet metal feature types

See Also

• Sheet Metal Shapes - Sheet metal recognition

• Feature Processor - General feature extraction