Feb 1911 min read

An Easy Introduction to Sheet Metal Design in CAD for Beginners

What is Sheet Metal Design in CAD?

Sheet metal design refers to creating 3D models of thin sheet metal parts using computer-aided design (CAD) software. It involves modeling the geometric shapes and sheet metal features like bends, holes, forms etc. that make up a sheet metal component.

Sheet metal parts are very different from machined or plastic parts. They are fabricated from thin sheet metal raw material like steel, aluminum, etc. which is cut and bent into the desired shapes. Common examples include brackets, enclosures, ducts, electronic chassis, panels, guards, and various housing components.

The key differences when designing sheet metal parts are:

The manufacturing process is sheet metal fabrication involving cutting, bending, punching etc. rather than machining or molding.
Dimensions and clearances for bends, seams, hardware insertion are critical. Sheet metal has little tolerance.
Bend radius limits, bend deductions, material thickness all impact the flat pattern shape.
Parts are designed as a folded assembly of flat pattern pieces rather than a solid body.

Using CAD for sheet metal design has many benefits compared to manual methods:

It's faster and more efficient to model sheet metal features in CAD.
CAD software automatically creates flat patterns, bend tables, and manufacturing drawings.
3D visualization enables analysing fit, clearances, assembly, manufacturability early.
Changes are easier to implement by modifying the CAD model versus redrawing.

Standard libraries of sheet metal parts, hardware, and information automate routine tasks.

Data and models can be easily reused for future projects.

In summary, sheet metal design in CAD enables efficient modeling of sheet metal components and greatly speeds up fabrication and manufacturing preparations.

Sheet Metal Design Software Options

Sheet metal parts can be designed in many different CAD (Computer Aided Design) programs. Some of the most popular options for sheet metal design are:

SolidWorks - SolidWorks is one of the most widely used CAD packages for sheet metal design. It has dedicated sheet metal features like flanges, sheet metal gauges, corner reliefs and more. SolidWorks makes it easy to convert 3D models into flat patterns for manufacturing.
AutoCAD - AutoCAD by Autodesk is a general purpose CAD program commonly used by designers and engineers. The sheet metal toolkit provides specialized tools for sheet metal including flanges, bends, corner reliefs and flat patterns.
Inventor - This 3D CAD software from Autodesk has robust sheet metal capabilities built in. Like SolidWorks, it includes features like flange/bend lines, corner treatments and flat pattern generation. Inventor integrates well with other Autodesk products.
NX - NX from Siemens is a high-end CAD package used for product development. It offers advanced sheet metal design tools for modeling complex sheet metal components. The flat pattern generator handles bends, corners and other features.
Creo - Formerly known as Pro/ENGINEER, Creo Parametric from PTC is another leading CAD app with dedicated sheet metal functions. It enables modeling of sheets, bends, holes, dimples and more.
Fusion 360 - This popular CAD package from Autodesk takes a parametric modeling approach. It provides sheet metal design features like flanges, sheet metal rules and flattened pattern views.

While all these programs have sheet metal capabilities, they differ in their specific tools, interfaces, pricing and integration with other software. For simple sheet metal parts, the basic features in any modern CAD program are sufficient. More complex designs may benefit from specialized sheet metal modules.

Sheet Metal Design Process Overview

The typical workflow for designing sheet metal parts in CAD follows these key stages:

1. Part Modeling

This involves creating the 3D CAD model of the sheet metal part, including all the critical features like bends, holes, slots, etc. The CAD model precisely defines the part geometry.

2. Sheet Metal Parameters

Once the 3D model is ready, sheet metal-specific parameters are added, like material thickness, bend radius, bend deductions, etc. This defines how the flat sheet metal blanks will be fabricated.

3. Unfolding the Flat Pattern

The software is used to unfold the 3D model to generate the flat pattern shape. This 2D pattern represents how the sheet metal blank needs to be cut before forming the 3D part.

4. Annotations and Drawings

Additional annotations and details are added to the flat pattern drawing, like bend lines, bend locations, dimensions, part number, material info, etc. This drawing guides the fabrication process.

5. Manufacturing Outputs

Finally, manufacturing outputs like flat pattern drawings, bend tables, blank information, etc. are generated from the CAD model. These help to produce the sheet metal parts efficiently.

This covers the typical high-level workflow for designing sheet metal components using CAD software. The key steps are creating the 3D model, defining sheet metal parameters, generating the flat pattern, adding annotations, and producing manufacturing outputs. Each stage provides vital information for fabrication and assembly.

Creating a New Sheet Metal Part File

The first step in any new sheet metal design is creating the part file with the correct sheet metal parameters, material properties, units, and thickness. This will ensure your sheet metal part is set up properly before modeling features.

Setting Sheet Metal Parameters and Material Properties

When creating a new part file, you'll want to specify that it is a "Sheet Metal" part. This activates specialized sheet metal features and tools. You can set material properties like steel, aluminum, etc. The material impacts forming simulations.

Specify relevant sheet metal parameters:

Bend radius - the default radius when creating bend features
K-factor - determines the bend allowance calculated for flat patterns
Inside bend radius vs. outside - which side takes the bend radius

Sheet Metal Gauges and Standard Thicknesses

It's important to assign the correct thickness to your sheet metal part by selecting a standard metal gauge. Common gauges are 0.5mm, 1mm, 1.5mm, 2mm, etc. Standard thicknesses result in accurate flat patterns.

Sheet Metal Units

Set units for sheet metal parts to mm or inches depending on industry standards. Verify units to avoid errors in downstream fabrication. Model sheet metal bodies to real-world dimensions for manufacturing accuracy.

Now your sheet metal part file is ready to model! Next we will cover modeling techniques for walls, flanges, and other sheet metal features.

Modeling Sheet Metal Features

Sheet metal parts have unique features like flanges, bends, and holes that need special modeling techniques in CAD software. Here are some of the most common sheet metal features and how to create them:

Adding Base Flanges and Walls

The foundation of any sheet metal part is the base flange that sets the initial shape and size. To create a base flange:

Draw a 2D profile sketch of the flange outline
Use the Convert to Sheet Metal command and define material parameters like thickness
The software will form an extruded 3D flange from the sketch

To make walls or sides for the part, draw another profile sketch perpendicular to the flange and extrude it. Make sure to join the walls to the flange to create a unified part.

Creating Bends, Folds and Hems

Bends and folds are what gives sheet metal its shape. To create them:

Draw bend line sketches where you want the bends
Use the Bend or Fold command and select the desired bend parameters
The software will form smooth rounded bends and folds along the sketch lines

For hems, draw an open hem profile then use the Hem command. The software will create a hem flange folded over on itself.

Cutouts, Holes, Lances and Slots

Sheet metal parts often need holes for fasteners, slots for adjustments, and cutouts for access. Here's how to make them:

Draw circular sketches for holes, rectangular sketches for slots
Use the Cutout command for holes and slots
For larger access cutouts, draw the profile and use the Cut command
Lances can be made with thin extrudes or the Lance command if available

Position all cutouts, holes and slots appropriately taking manufacturing into account. Remove any unwanted edges.

This covers the key techniques for modeling common sheet metal features like flanges, bends, holes and more. With practice, you'll be able to model sheet metal parts with the right features required for fabrication.

Sheet Metal Corners and Seams

When designing sheet metal parts in CAD, you'll need to create features like corners, bends, and seams where separate sheet metal pieces join together. Handling these areas correctly is important for both appearance and manufacturability.

Corner Reliefs

Inside corners between two bends or folds in sheet metal need extra space, called a "relief", to account for material thickness. Without a corner relief, the metal would collide with itself when bent. In CAD, you can automatically add corner reliefs of the correct size. This ensures proper spacing for material thickness.

To add a corner relief in a program like SolidWorks:

Click the "Sheet Metal" tab
Click "Corner Relief"
Select the corner(s) to apply the relief
The correct internal radius will be added

Corner reliefs should be applied whenever two bends intersect in a sheet metal part design. The relief size is normally equal to the material thickness.

Creating Seams and Joints

When two or more pieces of sheet metal come together, they are joined at a seam. Seams can be modeled in CAD along with other sheet metal features.

Some ways to create seams:

Flanged seams - Two sheets are bent outward along the joint with one sheet inside the other. Good for lap joints.
Hem joints - One sheet is folded over the edge of the other. Provides a clean finish.
Butt joints - Two sheet edges meet directly at the joint line. Needs welds or fasteners.

Joints connect the open edges of a seam. Adding weld symbols, holes for fasteners, or other joinery features completes the sheet metal assembly.

Properly designed seams and joints are crucial for assembly fit and structural rigidity. Take time to model them accurately.

Managing Gaps

Small gaps may appear between sheet metal components due to bending variation during manufacturing. In CAD, you can assign gap tolerances to joints so they assemble correctly despite minor gaps.

Some ways to manage gaps in sheet metal design:

Add gap dimensions to joint lines
Set gap tolerance assignments
Optimize bend sequence to minimize gaps
Use tab and slot features to allow play

Careful management of gaps in the 3D CAD model will help avoid fit issues when the parts are actually fabricated. Building in gap tolerance provides flexibility to accommodate reality.

Generating Flat Patterns for Sheet Metal Parts

Sheet metal fabrication starts with generating flat pattern sheets that can be cut and bent into the desired 3D shapes. CAD software automatically generates flat patterns once the 3D model is complete. Here is an overview of the key steps in creating flat patterns in CAD:

Flat Pattern Basics

The flat pattern represents the sheet metal part unfolded onto a 2D plane. All bends and features are flattened out.
CAD software uses the modeled part geometry to calculate bend angles and flattened dimensions.
Flat patterns show cut lines, bend lines, bend angles and other manufacturing details.
Initially the flat pattern is the shape of the projected part perimeter. Additional features get flattened.
Flat patterns must accurately reflect the 3D model to match the final fabricated part.

Unfolding Methods

There are different algorithms to unfold 3D sheet metal parts into flat patterns.
The most common method is to select bend lines and flatten each bend sequentially.
For complex geometry, flat patterns can also be generated by projecting edges onto a plane.
The unfolding direction and sequence can affect the generated flat pattern.

Flat Pattern Adjustments

The initial flat pattern may need tweaks for manufacturability.
K-factors can be used to compensate for material thickness at bends.
Relief features can be added to account for springback in the material.
Cut lines may need to be extended to ensure full cut through.
Additional bend lines can relieve residual stresses from the flattening process.
Flat patterns can be divided into smaller segments if needed for fabrication.

With the fundamentals covered, the flat pattern is ready for detailing, dimensioning and drawing creation. Accurate flat patterns are critical for manufacturing correct sheet metal parts. CAD software automates this complex process.

Adding Manufacturing Details

Once your sheet metal part design is complete in CAD, there are some final manufacturing details to add before sending it off for fabrication. These small but important tweaks will ensure your sheet metal part gets made correctly.

Bend Lines, Notes and Tables

When flat sheet metal is fabricated, it needs to be bent along specific lines to form the final 3D shape. Your CAD design should indicate where these bends occur through bend lines. They show up as dotted lines on the flat pattern. You can also add bend notes like "Bend 90°" to call out the bend angles.

Generate a bend table that lists each bend line, its angle, and any additional notes. This provides all the bending information nicely summarized for the fabricator. Make sure the bend notes in the table match what's on your flat pattern.

Punch Tool Details

Indicate any holes, slots or other punch tool operations on your flat pattern. Add notes with size and shape information so the punch tools can be selected appropriately. For example, "Ø.25 THRU".

Consider punch direction - some features may need to be punched before bending to allow tool access. Your notes should reflect the proper order of operations.

Final Tweaks

Do a final check of the flat pattern and 3D model before sending for fabrication. Look for any wireframe lines from early modeling steps and remove them. Delete any drawings or layers not needed for manufacturing.

Set your sheet metal thickness and correct material properties like gauge and alloy. Make sure your bend allowance and bend radius are properly set for the material gauge to generate accurate flat patterns.

With these last manufacturing details added, your sheet metal CAD design is ready for fabrication!

Tips for Efficient Sheet Metal Design

When designing sheet metal parts in CAD, there are some important tips and best practices to keep in mind for an efficient design and manufacturing process. Here are some key guidelines:

Use Appropriate K-Factor and Bend Radii

The K-factor determines the bend radius in relation to the thickness of the material. Using an appropriate K-factor prevents overly sharp bends and tearing of the material.
As a general rule, thicker materials require a larger bend radius. A k-factor between 0.4 and 0.5 works for most applications.

Avoid Small Flanges

Very narrow flanges can be difficult to fabricate consistently and lead to tolerance issues.
When possible, flanges should be at least 3 times the material thickness. Increase flange widths around holes and slots.

Design for Nested Manufacturing

Nest multiple parts within the raw material to minimize waste.
Align bend lines and features to allow for efficient nesting.
Use rectangular forms rather than irregular shapes when possible.

Standardize Similar Features

Use the same bend radius, hole sizes, fasteners etc. when possible for consistent fabrication.
Reuse existing 3D features like flanges or louvers to speed up design.

Include Sheet Metal Gussets

Gussets provide strength to joints and prevent distortion.
Strategically place gussets at stressed connections.

Troubleshoot Flat Pattern Issues

If the flat pattern shape is very irregular, the part may be difficult to manufacture. Simplify the geometry.
For inside bend radius errors, check for gaps in the bend area and ensure K-factors are set appropriately.
For errors in bend angle, examine the part closely for modelling issues causing incorrect angle calculation.

Following these tips will help create sheet metal parts that can be easily and efficiently fabricated while minimizing material waste.

Resources for Learning Sheet Metal CAD

There are many great resources available to help you improve your sheet metal design skills in CAD. Here are some recommendations:

Tips for Practicing and Improving Skills

Start by modeling simple sheet metal parts with just a few bends. Slowly increase the complexity as you gain confidence.
Sketch the flat pattern by hand first before modeling the 3D sheet metal part. This helps you visualize the flat pattern.
Pay attention to bend order and how you can control it when designing.
Model real sheet metal parts that interest you, like electronic enclosures or machine guards. Try matching measurements to the real objects.
3D print your sheet metal parts to inspect them physically before fabricating. Refine based on print results.
Read sheet metal design books and tutorials even after gaining proficiency. There are always new techniques to learn.

Next Steps After Mastering Basics

Try forming more complex geometric shapes like cones and curved faces.
Learn to integrate other design features like stamped holes, embosses, engraved text etc.
Understand manufacturing limitations related to minimum bend radius, K-factor etc.
Start applying sheet metal design principles like optimum bend deduction and joggle spacing.
Move on to multi-body sheet metal parts and top-down assembly modeling.
Look at integrating sheet metal parts with purchased standard hardware.
Brush up on sheet metal fabrication and manufacturing processes to make your designs more producible.
Collaborate with sheet metal fabricators and incorporate their feedback into designs.

With regular practice and referencing learning resources, you can steadily gain expertise in sheet metal CAD. Mastering the basics allows you to tackle more complex modeling, manufacturing and fabrication challenges.