Plastic and Sheet Metal Bending and Forming Guidelines

We’ve covered everything you need to know about plastic and sheet metal bending and fabrication for your laser-cut and CNC routed parts from SendCutSend. You should also check out our Designing for Bending page.
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Table of Contents

Plastic & sheet metal part setup & costs

Bending your metal and plastic parts adds a $19.00 minimum to your cart total.

Save up to 70% or more with quantity discounts! We calculate quantity discounts based on several factors including material, operation type, number of operations on each part and number of duplicate parts. Our app will automatically provide quantity discounts based on your order.

Check out our processing page for information about typical lead times for parts with bending and other services. We provide free 3-5 day shipping for standard orders (higher quantities may require additional time). Most bent parts will ship ground as they will exceed 2″ in height when packed.

Plastics & sheet metals available for bending

Material bending limits

  • 0.030” – 0.250” thickness
  • Minimum flat part size
  • Maximum flat part size
  • No 6061/7075 Aluminum
  • No Grade 5 Titanium
  • No AR400/AR500
  • No 1075 Spring Steel

What to know about plastics & sheet metal bending limitations

Before you start dreaming up your next project, you’ll need to know some of the metal and plastic bending limitations.

  • Maximum flat part size 44″ x 30″
  • Maximum bend length 16″ – 44″ depending on material thickness
  • Maximum thickness of .250”, depending on flange length
  • Maximum bend angle will depend on the material and thickness

Metal vs Plastic

Bending plastic is different! See our complete list of polycarbonate bending considerations.

Tolerances

Bent parts will have different dimensional and bend angle tolerances depending on the part size and material type.

Keep tolerance stackup for multiple bends in mind. Learn more about bending tolerances and how to plan accordingly.

No can do

While we’re happy to bend your parts to your hearts’ desire, there are some bends we don’t offer:

  • No acute angles greater than 130°
  • No obtuse angles less than 5°
  • No curl, bump, or roll forming
  • No coining
  • No hemming
  • For polycarbonate parts,
    no joggle bends

Our process: Air bending

At SendCutSend we form sheet metal and plastic with air bending.

Learn about air bending, its effect on bend radii, and polycarbonate considerations.

Die lines and feature distortion

Die lines are the full extent of the width of the tooling, or die, that we use to form parts.

When a part is bent, witness marks are left where the die makes contact with the part. These points of contact are what we refer to as die lines.

 

These points of contact (witness marks) are what we refer to as die lines

When cut features fall within the die lines or bend area, they will be distorted during the forming process when the material is stretched.

Learn how to avoid feature distortion in our Bending Deformation Guidelines.

Flange clearance

While designing parts with flanges that meet at a corner, keep in mind that collisions can happen. Our 3D bend previewer is a great reference tool for this!

Please note, we cannot guarantee that the preview will match your finished part perfectly. Be sure to select the material you’re designing with and use the specs from our Bending Calculator.

How to set up your file for plastic & sheet metal bending

Here are the basics you’ll need to know before you send us your first file for bending. If you have any questions, feel free to contact support.

Files accepted by our instant quote system:

Make sure the part design you upload for bending is either a 2D vector file (.dxf, .dwg, .ai, or .eps format) or a 3D .step or .stp format file. You will be able to view your bends in a 3D model during the checkout process to make sure the angles and flange orientations are correct.

SOFTWAREFORMATBEND LINE
Fusion.dxf, .step, .stpSolid line (default)
Adobe Illustrator.aiSolid, separate color from cut lines
SolidWorks.dxf, .step, .stpDashed line
(not hidden)
AutoCAD.dxf, .step, .stpDashed line
(not hidden)
CorelDraw.epsSolid, separate color from cut lines
Inkscape.epsSolid, separate color from cut lines

Please upload either a 2D .dxf, .dwg, .ai, or .eps format vector file or a 3D .step or .stp format file with your part design. 

If you design your parts in non-CAD software (Adobe Illustrator), please send us the original (native) .ai file.

We’ll take care of the conversion on our end. While we accept .ai and .eps files, it’s critical that your bend lines are parallel when uploaded from these softwares or the file will delay our process.

For the fastest turnaround on your order, we recommend designing your parts in CAD software.

To learn more about design guidelines for laser cut sheet metal, see our Laser Cutting Guidelines.

For CNC routed polycarbonate design guidelines, please see our CNC Machining Guidelines.

Working in Solidworks? Download our custom bend tables to specify exact bend allowances, bend deductions, and K-factors so your file is tailored to our manufacturing processes.

Bend lines in 2D files

If you upload a 2D vector file, we will use the flat .dxf, .dwg, .eps, or .ai file (if you use Adobe Illustrator) for cutting and bending, so please indicate bend locations in your drawing using a line. Bend lines should mark the center of each bend.

See our troubleshooting tips if your bend lines don’t show up after uploading your file.

During the ordering process, you can specify bend angles for each line. You will receive an error message in the app if your bend line is missing or insufficient.

  • Use any color you wish, line colors are ignored by our system.
  • If using Adobe Illustrator, DO NOT use dashed lines, and make sure your lines are parallel to one flat edge.

 

Reference our bending export guides for assistance exporting cut-ready files.

Bend lines mark the center of each bend

3D file considerations

If you plan to submit a STEP/STP format file, see our 3D File Guidelines.

Ensure your sheet metal rules are set up with SendCutSend’s specifications for bend radius and K factor for the material desired.

Tip: you don’t need to worry about bend lines if you’re uploading a STEP/STP file. Model your part, set your bend definitions, save your file, and upload for an instant quote.

Learn how to configure STEP file bends when instant quoting your parts.

Formed part dimensions

We make the parts you send us! Use the correct material specifications from our website to ensure your bent parts turn out as expected. 

SendCutSend Bending Calculator

How To Find Material Specifications

This example shows the difference between flat and formed part dimensions in 0.125” 5052 aluminum.

Flange and base

Before we begin, some basic terms you’ll need to know are base and flange. The flange is the edge you will be bending.

Minimum and maximum flange length

The minimum flange length will change depending on what material and thickness you use. Please reference your chosen material in our Material Catalog to see the correct dimensions under Material Details.

Learn how to measure flanges and find specifications for materials thicknesses.

The maximum flange length for 4-sided box bends will depend on the material choice and whether hardware will be installed. With hardware, the maximum flange length is 3.00″.

Learn more about maximum flange lengths on 4-sided box bends.

Acute and obtuse bends

The bend angle is measured on the outside of the bend. In the illustration below, you will see that the acute bend is being called out as 130°.


Learn more about bend angle callouts and how to enter bend definitions when ordering.

Note: the bend angle limits and bend radius for your part can be found on the material page. We do not offer a custom bend radius.

C-Channel or U-Channel bends

2:1 ratio for sheet metal

Sheet metal parts

For u-channel bends in sheet metal, the base must be at least 2 times wider than the flange length in most cases.

However, the 2:1 ratio rule for sheet metal parts can be flexible for thinner materials that meet specific criteria.

Learn about exceptions to the 2:1 base-to-flange ratio rule for sheet metal u-channel parts.

Polycarbonate parts

For u-channel bends in polycarbonate, the base must be at least 3 times wider than the flange length (3:1 ratio).

3:1 ratio for polycarbonate

How to spec window or joggle bends in plastics & sheet metals

Window bends are allowed up to 90° for sheet metal and polycarbonate parts. More acute angles require review by our team.

Learn about our window bend design requirements.

Joggle bends are allowed up to 90° for sheet metal parts only. You can find the minimum and maximum joggle flange values on the specification charts for your chosen material.

Learn about our joggle bend design requirements.

What to do if you need a sheet metal bend with an odd flange shape

While we do allow for irregular shapes for your flange, we will need a flat piece to bend. To do this, add tabs to make a flat surface parallel to the bend.

Ensure your tabs are long enough for your part and include enough connecting bridges. See our complete guide on setting up breakoff tabs for odd flanges.

Bend relief notches

To reduce bulging in the corners of your bent parts and prevent tearing, incorporate bend relief notches into your design.

These notches allow for less stress on the inner radii of the flanges and will help keep the corners of the bends from interfering with the base material.

Learn more about our bend relief requirements for polycarbonate and sheet metal parts.

Mirrored parts

If you need some of your parts to “mirror” others, split mirrored parts between separate line items and specify opposite bend directions.

You can use the Duplicate item button in your shopping cart to expedite this!

Learn more about ordering mirrored parts.

What to expect when bending plastics & sheet metal parts

General

  • Witness marks from the bending process will be visible; these can become deeper and more noticeable depending on the material
  • We do not offer special protection for cosmetic parts at this time
  • Some bulging at the ends of the bend will be expected

 

Polycarbonate

  • Polycarbonate parts may have minor surface edge cracks depending on the material thickness and bend angle
  • Polycarbonate parts will have noticeable cracking in stressed areas if adequate relief is not provided for each bend
Witness marks from bending process

How to prevent common issues with plastic & sheet metal bending

Combined lines

Bends on a common axis need to be joined, as in the example shown here. If they are not joined, each bend will be seen individually.

Intersecting bends

We are unable to bend intersecting lines that do not have separate flanges.

Insufficient or missing bend relief

Certain designs require bend relief to avoid damage to the part. Without proper relief, a part cannot be bent accurately. This is a critical consideration for polycarbonate parts since the material is prone to cracking. Check out our guide to designing bend reliefs and Bending Deformation Guidelines for more information.

You’re ready to bend

Although metal and plastic forming is a deeply complex process, we here at SendCutSend aim to make part bending as easy as possible. Questions? Reach out to our support team.

Happy bending!

Pre-flight checklist

Additional Resources

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