Bend radius and bend allowance in Solidworks - Step-by-Step Guide

Introduction

Bend radius and bend allowance help you control how metal sheets bend in your design. They solve the problem of predicting the final shape and size after bending, so your parts fit perfectly.

When designing sheet metal parts that need precise bends for assembly.

When calculating material length before bending to avoid waste.

When adjusting bend settings to match manufacturing capabilities.

When creating flat patterns for laser cutting or CNC machines.

When ensuring parts meet tolerance requirements after bending.

Steps

Step 1: Open your sheet metal part

- FeatureManager design tree

The part model appears with sheet metal features visible

Step 2: Click the Sheet Metal tab

- CommandManager

Sheet metal tools become available

Step 3: Select the Bend feature

- Sheet Metal tab

Bend property manager opens for input

Step 4: Enter the desired Bend Radius value

- Bend property manager

The bend radius updates and the model preview changes to show the bend curvature

💡 Use a radius that matches your manufacturing tool to avoid errors

Step 5: Check or adjust the Bend Allowance

- Sheet Metal Parameters in the Sheet Metal tab

The flat pattern length updates to reflect the bend allowance

Step 6: Click OK to apply the bend

- Bend property manager

The bend is added to the model and the flat pattern updates accordingly

Before vs After

Before

Flat sheet metal part with no bends and length 100 mm

After

Sheet metal part with a 5 mm bend radius and bend allowance applied, flat pattern length updated to 104 mm

Settings Reference

Bend Radius

📍 Bend property manager

Controls the inside radius of the bend to match tooling and material behavior

Default: Material thickness

Bend Allowance

📍 Sheet Metal Parameters in Sheet Metal tab

Adjusts the length added to the flat pattern to account for material stretch during bending

Default: Automatic

K-Factor

📍 Sheet Metal Parameters

Defines the neutral axis position inside the material thickness for bend calculations

Default: 0.5

Common Mistakes

Using a bend radius smaller than the material thickness

This can cause material cracking or tool damage during manufacturing

Set the bend radius equal to or larger than the material thickness

Ignoring bend allowance and using flat length equal to sum of straight segments

The part will be too short after bending because material stretches

Use bend allowance or K-factor settings to calculate correct flat length

Summary

Bend radius controls the curve size of sheet metal bends to match tooling.

Bend allowance adjusts flat pattern length to account for material stretch.

Correct settings ensure accurate final part size and fit after bending.

Practice

1. What does the bend radius represent in sheet metal design?

easy

A. The inside curve size of the bend

B. The thickness of the sheet metal

C. The total length of the flat pattern

D. The angle of the bend

Solution

1. Step 1: Understand bend radius definition

   Bend radius is the radius of the inside curve where the metal bends.

2. Step 2: Differentiate from other terms

   Thickness is metal thickness, length is flat pattern size, angle is bend angle, so they are incorrect.

3. Final Answer:

   The inside curve size of the bend -> Option A

4. Quick Check:

   Bend radius = inside curve size [OK]

Hint: Bend radius is always the inside curve size [OK]

Common Mistakes:

• Confusing bend radius with metal thickness
• Thinking bend radius is the bend angle
• Mixing bend radius with flat pattern length

2. Which of the following formulas correctly represents bend allowance (BA) for a bend with angle θ (in degrees), bend radius R, and thickness T?

easy

A. BA = (π/180) x θ x (R + T/2)

B. BA = (π/180) x θ x (R - T/2)

C. BA = (π/180) x θ x (R + T)

D. BA = (π/180) x θ x R

Solution

1. Step 1: Recall bend allowance formula

   Bend allowance = angle in radians x (bend radius + half thickness).

2. Step 2: Convert angle to radians and apply formula

   Angle θ in degrees converted by (π/180), then multiplied by (R + T/2).

3. Final Answer:

   BA = (π/180) x θ x (R + T/2) -> Option A

4. Quick Check:

   Bend allowance = angle x (radius + half thickness) [OK]

Hint: Add half thickness to radius in bend allowance formula [OK]

Common Mistakes:

• Using full thickness instead of half thickness
• Omitting thickness in the formula
• Using radius minus half thickness

3. Given a sheet metal bend with bend radius 7 mm, thickness 2 mm, and bend angle 90°, what is the bend allowance using the formula BA = (π/180) x θ x (R + T/2)? (Use π ≈ 3.14)

medium

A. 10.5 mm

B. 12.56 mm

C. 15.7 mm

D. 13.23 mm

Solution

1. Step 1: Calculate (R + T/2)

   R = 7 mm, T = 2 mm, T/2 = 1 mm, so R + T/2 = 8 mm.

2. Step 2: Convert 90° to radians

   (3.14 / 180) x 90 ≈ 0.01744 x 90 ≈ 1.57 radians.

3. Step 3: Compute bend allowance

   BA = 1.57 x 8 = 12.56 mm.

4. Final Answer:

   12.56 mm -> Option B

5. Quick Check:

   (π/180) x 90 x 8 ≈ 12.56 mm [OK]

Hint: Multiply angle in radians by (radius + half thickness) [OK]

Common Mistakes:

• Forgetting to convert angle to radians
• Using full thickness instead of half thickness
• Incorrect π value or rounding errors

4. Identify the error in this bend allowance calculation code snippet:

angle = 90
radius = 5
thickness = 2
bend_allowance = (3.14 / 180) * angle * (radius - thickness / 2)

medium

A. Thickness should be doubled, not halved

B. Angle should be in radians, not degrees

C. Using radius minus half thickness instead of adding

D. π value is incorrect

Solution

1. Step 1: Review bend allowance formula

   Correct formula uses (radius + half thickness), not minus.

2. Step 2: Check code snippet

   Code uses (radius - thickness / 2), which is incorrect and will underestimate bend allowance.

3. Final Answer:

   Using radius minus half thickness instead of adding -> Option C

4. Quick Check:

   Bend allowance uses radius + half thickness [OK]

Hint: Always add half thickness to radius in formula [OK]

Common Mistakes:

• Subtracting half thickness instead of adding
• Not converting angle to radians
• Using wrong π value

5. You need to create a flat pattern for a sheet metal part with a 120° bend, bend radius 4 mm, and thickness 1 mm. Which bend allowance should you use to ensure accurate flat length?

hard

A. BA = (π/180) x 90 x (4 + 1/2) = 7.07 mm

B. BA = (π/180) x 120 x (4 - 1/2) = 7.54 mm

C. BA = (π/180) x 180 x (4 + 1) = 15.7 mm

D. BA = (π/180) x 120 x (4 + 1/2) = 9.42 mm

Solution

1. Step 1: Identify correct formula and values

   Use BA = (π/180) x angle x (radius + half thickness). Angle = 120°, radius = 4 mm, thickness = 1 mm.

2. Step 2: Calculate bend allowance

   Half thickness = 0.5 mm, so radius + half thickness = 4.5 mm.
   BA = (3.14/180) x 120 x 4.5 ≈ 2.09 x 4.5 = 9.42 mm.

3. Final Answer:

   BA = (π/180) x 120 x (4 + 1/2) = 9.42 mm -> Option D

4. Quick Check:

   Bend allowance uses angle 120° and radius + half thickness [OK]

Hint: Use angle x (radius + half thickness) for bend allowance [OK]

Common Mistakes:

• Using wrong bend angle
• Subtracting half thickness
• Doubling thickness instead of halving