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Designer inserting a thermoforming template inside the Mayku Multiplier (pressure forming machine)
Close up image of a thermoforming template made with an SLS 3D Printer (Formlabs Fuse 1)

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How to design for thermoforming

Discover the main design principles needed to create high quality thermoforming templates

Before getting started on any thermoforming project, it is essential to understand the design principles that apply to thermoforming templates. This will allow you to transform your idea into a real product as effectively and efficiently as possible. In this article, we’ll examine the main design principles of thermoforming.

Here are a few of the best practices that you should know before you start designing thermoforming templates. You can use them to design from scratch or adapt an existing 3D design to which you already have access.

As a general rule, undercuts should be avoided. If you form a model with ledges or indentations, you won’t be able to remove the object once the plastic sheet cools down. Although with Mayku EVA Sheets, you can create templates with small undercuts, as well as embossed text on vertical walls.  

Graphic showing the recommended undercuts when designing theromforming templates
Thermoforming template design: Undercut recommendations

A draft angle is a slant that is applied to the faces of your model that enables easier release of a template from a plastic sheet. The more draft, the easier it is to remove a part from a template, as well as achieve uniform thickness. Specifically, we recommended a minimum of a 5° draft angle to achieve the best possible forming and template release. 

Graphic on thermoforming template design: recommended draft angle
Thermoforming template design: recommended draft angle

Technologies such as 3D printing or CNC milling are suitable for manufacturing templates with draft angles. However, draft angles are not possible when using manufacturing methods such as laser cutting. In these cases, you can add “steps” consisting of an inclined plane with multiple small steps, rather than a single, large vertical wall. 

How to design for thermoforming: draft angle when using laser cutting to make templates
Laser cut template featuring steps on its surface to compensate for the lack of draft angle

Wide parts are easier to form than tall ones. This means you should strive to create templates that are wider than they are tall – or use generous draft angles to compensate.

Thermoforming template design: width vs. height

The better air flows through a thermoforming template, the higher the final part quality. By adding air holes to a template, you can create parts or molds with higher degrees of detail and prevent air bubbles.

Some template designs may have features such as cavities that can generate air pockets during the forming process. By adding air holes to these cavities, air can be evacuated during the forming process, resulting in a more detailed part.

Templates that must exhibit sharp corners or small surface details are good examples of those that can benefit from air holes. If your template features sharp steps on its outer surface, you can add air holes near the step edges to ensure the plastic sheet reaches the edge during the forming process. 

Graphic showing thermoforming template design: capturing details with air holes
Thermoforming template design: capturing details with air holes

The amount of air holes you need will depend on the template design. Air holes should be used sparingly, and always placed near edges and corners in a part’s cavities. They should also be small enough so that they are not readily noticeable on the final part. We recommend using tapered air holes, which are no more than 0.4mm on a template’s surface and no more than 2mm on the bottom of a template.

Thermoforming template design: using air holes to prevent air bubbles
Thermoforming template design: using air holes to prevent air bubbles

This is especially useful when using SLA 3D printing, as resin can easily become trapped in small air holes. If air holes are too large and the material used is thin, however, the sheet may pop during the forming process, ruining the part.

Autodesk Fusion 360 screenshot showing a thermoforming template and its tapered air holes
Tapered air holes on a thermoforming template

A plastic sheet’s surface area will increase when it is formed into a three-dimensional shape. It will also become less thick. Templates with different shapes and features, however, have different sheet thinning ratios. For example, if a template doubles a plastic sheet’s surface area, its average thickness will decrease by half. It is also important to note that a part’s final thickness is typically inconsistent – meaning some areas will be thicker than others.

The sheet thinning ratio is crucial if your template has a cavity. In these cases, be sure that the cavity’s depth is no more than two-thirds of the width of its surface opening. Any larger and the risk of a final part with a surface that is too thin dramatically increases.  
 

Thermoforming template design: cavity depth
Thermoforming template design: cavity depth

Thermoforming isn’t always suited for templates that have sharp angles (smaller than 90º). Along with minimal draft angles, sharp vertical corners are more likely to cause a plastic sheet to web and tear during forming. To avoid this and improve part quality, be sure that all of a template’s corners and edges are round.

Thermoforming template design: sharp corners
Thermoforming template design: sharp corners

Thermoformed parts can replicate a template’s surface texture even if that texture is not visible, so you should keep this in mind while designing. If you’re attempting to create a part with a smooth surface, you may need to post-process it.

The amount of post-processing needed will differ depending on the technology used to create a template. With FDM 3D printing, for example, you will typically notice more layer lines than with a template created with SLA 3D printing.

It’s possible to manufacture parts with the Mayku Multiplier with detail resolution as small as one micron. In these cases, you may need to lightly sand your final part to achieve your desired finish, even if it was created with SLA 3D printing.  

Image showing the surface texture generated on a thermoformed part when using an FDM 3D printed thermoforming template
Surface texture generated when using an FDM 3D printed template

While following thermoforming’s design principles is essential to success, choosing the right template manufacturing method is also crucial. For this, you can read our article on technologies to create templates. It will better enable you to find the template manufacturing method that best fits your needs.

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