Sample tool

The 3 tools  that come in the Maker Kit are helpful tools for learning the design principles of the thermoforming and the FormBox as they include undercuts, draft angles, and air holes. 

Here are a few of the best practices for designing a tool for thermoforming: 

 

Maximum tool volume

The size of the FormBox bed is 200mm x 200mm. The maximum width and length you are able to mold is 150mm x 150mm. To avoid tearing the plastic, we suggest not vacuum forming anything taller than it is wide. 

 

Undercuts

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 tool once the plastic sheet cools down. An exception to the rule is when forming with Mayku EVA Sheets —  in this case, you can use tools with small undercuts, as well as embossed text on vertical walls due to the flexibility of the EVA material.

Undercuts should be avoided where possible as they can restrict demolding and cause materials to overstretch. If your design requires undercuts, consider creating a tool consisting of multiple slotting parts to help release the formed part.

Where necessary consider the following:

• Using a flexible material such as EVA
• Creating a tool consisting of multiple slotting parts to help release the mold.
• Create a cutting path within your tooling to help release.

 

 

Draft angles

A draft angle is a slant that is applied to the faces of your model to enable easier release of a tool from a plastic sheet. The greater the draft, the easier the de-molding process.  It also helps to achieve uniform sheet thickness. Specifically, we recommended a minimum of a 5° draft angle to achieve the best possible forming and tool release. 

Degree recommendation for material type:

Rigid materials (e.g. Clear Sheets (petg), Form Sheets (HIPS) = 8° draft angle

Flexible materials (e.g. Flex sheets)) = no draft angle required

Height vs. width

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

Air holes

You may need to add air holes to your tool, depending on the material that your tool is made from. There are different rules for porous and non-porous tool materials.

• Porous materials: air holes are not needed for porous materials e.g SLS nylon, open cell compositions, aluminum resin composite billets & some polyurethane boards. 
• Non-porous materials: air holes are needed for non-porous materials e.g FFF nylon & high temp SLA resin (including handmade tools).

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

Some tool 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.

The number of air holes you need will depend on the tool design. Air holes should be used sparingly and always placed near edges and corners in a part’s cavities. They should be small enough that they are not readily noticeable on the final formed part. We recommend using tapered air holes, which are no more than 0.5mm on a tool’s surface.

 

Recommended air hole size for different 3D printing technologies:

• SLA 3D Printing: 0.5mm diameter tapered air hole. As small as your printer can do, commonly 0.4/0.5mm.
• FDM 3D Printing: 0.5mm diameter tapered air hole. As small as the resolution of the printer, larger than 0.5mm may be required in some cases.
• SLS 3D Printing: No air holes needed due to tool porosity.
• Handmade Tools: 0.5mm or as small as you can 

Air hole size and shape are important considerations when using SLA 3D printing and FDM 3D printing, as resin can easily become trapped or filament can build up inside small air holes compromising the forming quality. On the other hand, if air holes are too large and the sheet material used is thin, the sheet may pop during the forming process, resulting in a ruined part.

 

Sharp angles

Thermoforming isn’t always suited for tools that have sharp angles (less than 90º). Sharp vertical corners are more likely to cause a plastic sheet to web and tear during the forming process. To avoid this and improve final part quality, ensure that all of a tool’s corners and edges are rounded.

       

 

Corner radius

During the thermoforming process, the heated sheet material gradually conforms to the shape of the tool and becomes fixed in place due to cooling. As the material approaches corners, it thins out due to stretching.

To ensure consistent part thickness and improve structural strength, round the corners and edges. The corner radius facilitates the consistent flow of material.

Male vs. Female tools

During the vacuum forming process, tools (templates) are used to create molds for casting or end parts depending on the application.

A male tool is defined by positive or convex features, while a female tool is defined by negative or concave features.

 

                         

In vacuum forming, male templates are more common, in particular if you are forming a mold to cast chocolate, jesmonite, soap, candles etc or forming basic packaging with minimum detail.

In the example below, the green colour indicates the side of the tool in contact with the sheet material, and which have the highest level of detail.

The side of the material touching the tool-face is the most accurate for dimensions. To ensure an accurate fit, define it by the material face contacting the tool.

 

(Above) Part formed using a male tool: green shading indicates surfaces that are in contact during the forming process, and where the ultra high detail is picked up.

 

 

(Above) Part formed using a female tool: green shading indicates surfaces that are in contact during the forming process, and where the ultra high detail is picked up.

 

Steps

Technologies such as 3D printing or CNC milling are suitable for manufacturing tools 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. This method also works when layering card, or plywood.

 

                           

 

 

 

Cavity depth

A plastic sheet’s surface area will increase when it is formed into a three-dimensional shape, causing the material to stretch and reduce in thickness. Tools with different shapes and features, have different sheet thinning ratios. For example, if a tool 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 to consider if your tool 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 made with material that is too thin dramatically increases.  

Tool placement

Placing multiple tools close to each other can lead to webbing during the forming process. To avoid that, consider leaving a gap greater than the height of the tallest tool or design feature.

This rule applies mostly to male molds, where webbing negatively affects the final part. It has a lower impact on female tools, as the webbing won’t affect the final part, which is on the inside.

Learn More in MultiplierDesign Principles for Tooling

 

Choosing the right technology to make a tool

While following thermoforming’s design principles is essential to success, choosing the right tool manufacturing method is also crucial. For this, you can read our article on technologies to create tools.

It will better enable you to find the tool manufacturing method that best fits your needs.