Surface, Sheet Metal, and Knowledgeware - Practical Guide

CATIA · GSD · Sheet Metal · Knowledgeware

Overview

Complex surfacing, sheet metal, and rule-based automation are areas that Part Design alone cannot cover.

This page weaves Generative Shape Design (GSD), FreeStyle / ICEM Shape Design (Class A), Sheet Metal (GSM / ASL), Weld / Structure Design, and Knowledgeware (Parameter, Formula, Rule, Check, Design Table) into a single flow.

Refer to page 02 for Part Design basics and page 03 for Assembly.

1. Generative Shape Design (GSD)

1.1 Overview and Containers

GSD is the free-form modeling workbench built around Surfaces + Wireframe. It is essential for automotive body panels, consumer-electronics exteriors, and organic shapes, and it coexists with the Body inside the same .CATPart as Part Design.

There are two container types in the Tree.

Geometrical Set — a container for Curves / Surfaces (no order)
Ordered Geometrical Set — preserves order (sequential, like Part Design)

Tip In most real-world work, the Ordered Geometrical Set is preferred. It makes feature order traceable and plays well with Design Tables.

1.2 Wireframe Fundamentals

Point (Coordinates / On Curve / On Plane / On Surface / Extremum / Between), Line (Point-Point / Point-Direction / Angle / Tangent / Normal / Bisecting), Plane, Projection / Intersection, Circle / Corner, Connect Curve (G0/G1/G2), Spline, Helix, Spiral, Spine, Isoparametric Curve, Boundary, Polyline.

Tip Surface quality is decided by the quality of the underlying wireframe. Trim Spline control points to the minimum needed and apply Tangent conditions explicitly, and the Class quality of downstream Sweeps and Lofts improves dramatically.

1.3 Surface Creation

Extrude / Revolute / Sphere / Cylinder / Offset
Sweep — four flavors: Explicit (profile + guide), Line, Circle, Conic
Multi-Sections Surface (Loft) — Sections + Guides + Spine
Blend — connect two curves / surfaces with continuity control (G0 – G3)
Fill — fill a closed boundary with a face
Adaptive Sweep — advanced sweep that varies the profile per position
Bump / Shape Morphing / Wrap Surface — deformations

1.4 Operations

Join — combine. Merge Distance, Check Connexity, Check Manifold.
Heal — force-close small gaps (accuracy penalty, careful)
Disassemble — multi-cell → single-cell
Split / Trim — Split keeps one side, Trim cuts both sides
Extract / Extrapolate / Fillet / Shape Fillet
Translate / Rotate / Symmetry / Scaling / Affinity / Axis To Axis

Tip Trim has the two Surfaces cut each other. When you only want to cut one Surface, use Split. They serve different purposes; reaching for Trim reflexively can edit a reference Surface unintentionally.

1.5 Continuity (G0 – G3)

Level	Meaning	Quality
G0	Point continuity, mere contact	Visible edge
G1	Tangent continuity, matching tangent directions	No visible edge
G2	Curvature continuity, matching curvature	No reflection distortion
G3	Continuity up to the rate of curvature change	Top Class A quality

Class A typically requires G2 or better, and highly reflective surfaces demand G3.

1.6 Analysis Tools

Connect Checker — gap / tangency / curvature continuity check
Feature Draft Analysis — draft angle (ejection feasibility)
Surface Curvature Analysis — Gaussian / principal curvature color map
Porcupine Curvature Analysis — curve-curvature "porcupine"
Distance Analysis — color map of distance between two surfaces
Environment Mapping (Highlight) — lighting-reflection simulation

Tip Watching whether the virtual fluorescent-tube stripes flow smoothly across an Environment Mapping is the definitive check for Class A quality on automotive body panels.

1.7 GSD Practical Tips

Build Reference Elements (Point / Line / Plane / Axis System) first, then go Curve → Surface
In Multi-Sections / Sweep, Spine quality drives the result
Keep the CV (Control Vertex) count minimal for higher Class quality
Use Shell for thin, uniform thickness; Thick Surface for non-uniform thickness
Treat gaps with Join (Merge Distance); reserve Heal as a last resort

2. FreeStyle · ICEM Shape Design (Class A)

2.1 FreeStyle Shaper

A NURBS + Subdivision hybrid workbench. For early concept and prototyping.

3D Curve / Planar Curve
Styling Sweep / Match Curve
Net Surface (a surface from a curve grid)
Styling Fillet / Blend
Global Deformation
Direct Control-Point manipulation

Tip FreeStyle output is generally considered "Class B". Use it for studies and concepts, not final exterior-panel delivery.

2.2 ICEM Shape Design / ICEM Surf

Dedicated to Class A. It is the standard at automotive OEMs (BMW / Audi / Mercedes / Hyundai-Kia studios).

Direct Modeling (manipulating NURBS CVs directly)
Feature-based Hybrid (Boolean, G3 Fillet)
Zebra / Highlight / Porcupine / Reflection quality analysis
G0 – G3 Surface Matching
Constrained Deformation

ICM is an integrated workbench inside CATIA, whereas ICEM Surf is a standalone application.

The typical workflow is studio designs in ICEM Surf → engineering imports into CATIA → engineering refines in GSD.

2.3 STRAK / Class A Workflow

Import reference surfaces from the design studio
Primary Surface — large outer panels, 4-sided patches, Degree 5 – 7
Tension Surface — connects primary surfaces, G2 continuous
Fillet / Blend — variable R or conic
Quality Analysis — verify G2 or better with Zebra / Highlight
Data Exchange — hand off to engineering via STEP AP214 or native

Note Class A is a dual standard — geometric accuracy plus aesthetic quality. Surfaces meeting is not enough; the reflection stripes must flow smoothly.

3. Sheet Metal Design

3.1 Generative Sheet Metal Design (GSM)

Used for general industry (electronics cabinets, machinery covers).

Initial Sheet Metal Parameters are the premise of every unfold calculation.

Thickness — sheet thickness
Bend Radius — default bend radius
K Factor — neutral-axis position (0 – 0.5)

K Factor (DIN) approximation: K = 0.65 + log₁₀(R/T) × 0.5 — R is the inner bend radius and T is the thickness.

Note If the K Factor differs from the actual shop process, the unfolded length is off and blank cutting drifts. Agree this with process engineering before design freeze.

3.2 Wall / Flange / Stamp

Wall — base panel from a Sketch or Edge. Add an orthogonal wall with Wall on Edge.
Flange — Spine (edge) + Radius + Length + Angle. The most common bend.
Hem — 180° folded-over edge
Tear Drop — teardrop curl
User Flange — flange from an arbitrary profile
Bend / Conical Bend / Bend from Flat
Stamping Features — Surface Stamp, Bead, Curve Stamp, Flanged Cutout, Louver, Bridge, Circular Stamp, Dowel, Half Pierce

Tip Stamps can be linked to a Design Table to pull DIN / ISO standard sizes by row selection alone. Registering them under Tools → Stamp Catalog lets the team share them.

3.3 Folding / Unfolding

Unfold All / Fold — unfold or refold everything
Unfold — target a single Bend
View from Unfold / From Folded — auto-generate the unfolded view in the drawing

Note Unfold can error out when Stamps or User Flanges are present. Work around it by ticking Tools → Options → Sheet Metal → Ignore Stamps in unfolding.

3.4 Aerospace Sheet Metal Design (ASL)

Specialized for aerospace. Supports hydroforming and break-form processes.

Dedicated features: Web (main sheet), Flange (Curved / Double Curved / Planar), Flange Cutout / Hole / Slot, Joggle (stepped bend), Stiffening Bead / Rib, Hem / Tear Drop, Corner Relief.

Tip Unlike GSM, ASL supports curved sheet metal (Double Curved Flange), which is mandatory for curvature-driven skins such as fuselage panels.

3.5 Sheet Metal Practical Tips

Expose Thickness and Radius as Parameters to propagate sheet changes in one shot
Default tolerance ±0.1 mm, precision parts ±0.05 mm
Annotate the Grain Direction
Pick the Unfolded View type in the drawing to auto-generate the flat pattern

4. Weld Design · Structure Design

4.1 Structure Design

Modeling beam / column structures.

Section Catalog — standard sections: H-beam, I-beam, Angle, Channel, Tube, Pipe, etc.
Place Beam — a beam between two Points / Axes
Place Plate — a connector plate
End Cut — trim a beam end to meet its mate
Trim — beam trim

Tip A Beam in Structure Design is not a simple Extrude — it is a Beam Feature carrying section, length, and connection data. It powers automatic Steel BOM extraction downstream.

4.2 Weld Design

Fillet Weld / Square · V · Bevel · U · J Butt
Spot Weld — thousands per vehicle in automotive BIW
Plug / Seam / Slot Weld
Weld Feature — 3D solid representation of the deposited metal
Automatic Edge Trimming — edges auto-cleaned per weld type

Tip Welding symbols assigned through Weld Design propagate automatically into Drafting as annotations. Quality control is far easier than with hand-placed annotations.

4.3 Automotive Spot Welds

A single automotive BIW carries 3,000 – 5,000 spot welds. The shop-floor standard is to combine Weld Design + Macro for batch pattern creation, and to use Knowledgeware Rules to auto-space spots along an edge (see the Macro section on page 06).

5. Knowledgeware

5.1 Parameter

Path: Tools → Formula, or the f(x) icon.

Supported types: Real, Integer, String, Boolean, Length, Angle, Mass, Volume, Time, Temperature, Force, Pressure, List, Point / Line / Plane / Body / Part, etc.

Tip Do not lean on feature names — explicitly declare meaningful Parameters, which makes Design Table and Rule integration easy. Naming examples: Param_Length, Cfg_BoltDiameter, Ref_WallThickness.

5.2 Formula

Relations among Parameters.

PadLength = PartBody\Pad.1\FirstLimit\Length
          + PartBody\Pad.1\SecondLimit\Length
TotalVolume = Pi * Radius**2 * Height

Function library: sin(), cos(), log(), sqrt(), min(), max(), if(), isin(), and so on.

Tip Use the if (Length > 100mm, 10mm, 5mm) form for conditional dimensions. Omit the unit and you get a unit-mismatch error.

5.3 Rule

Executes conditional actions in the Knowledge Advisor workbench.

if (Wall_Thickness < 2mm)
{
    Message("Warning: thickness too low")
    Bolt_Diameter = 6mm
}
else
{
    Bolt_Diameter = 10mm
}

5.4 Check

Warns on condition violations. Used for automated validation.

Check: TransitionRatio = Transition / Depth
TransitionRatio >= 4
Message: "Taper ratio of 4 or greater recommended (safety-factor margin)"

You can pick between a yellow warning and a red block (Silent / Block) mode.

5.5 Design Table

Configuration management backed by Excel / TXT.

Tools → Formula → Design Table icon
Create a design table with current parameter values
Pick Parameters → generate an .xls file
Add rows in Excel → extend the configuration
Pick a row in CATIA → model updates to those dimensions

Use Case: Swap through an M4 / M6 / M8 / M10 / M12 bolt series inside a single .CATPart with just a row selection. Combined with a Catalog, you can drag-and-drop it into an assembly directly.

5.6 Power Copy and UDF

Power Copy — a reusable feature group. Instantiate by feeding inputs from another Part.
UDF (User-Defined Feature) — similar to Power Copy but internally encapsulated (private)
Document Template — templated Parts / Products

Use Case: Turn the in-house standard "stiffening rib" pattern into a Power Copy and roll it out to the team. Another Part can reproduce the same rib by picking two edges and one dimension.

Field Checklist

Is Ordered Geometrical Set preferred in GSD?
Are Spline control points minimized to secure Class quality?
Is the Spine of your Sweep / Loft properly defined?
Is G1 / G2 continuity checked regularly with Connect Checker?
Was Zebra / Highlight quality analysis performed for Class A work?
Were the Sheet Metal Parameters (Thickness, Bend R, K Factor) locked in up front?
Was the K Factor agreed with the shop-process owner?
Was Unfold feasibility pre-checked for sheet metal containing Stamps?
Is automatic annotation propagation set up via Weld Design?
Has the team agreed on a Parameter naming convention?
Are standard part series managed with Design Table + Catalog?
Are repeated patterns templated as Power Copy / UDF?