[Pressure Forming] 12 Thermoforming Design Principles Every Beginner Should Know
Why do I always fail when making molds using hot pressing? And why do the molds wrinkle and deform? Understanding the design principles of pressure forming molds is absolutely crucial before starting any pressure forming project!
This article summarizes many essential basic techniques for 3D printing combined with pressure molding, which can save you a lot of time, materials, and unnecessary detours. Let's learn together!!!
For a better understanding of the application guidelines for individual technologies such as Hot Melt Deposition (FDM), Laser Powder Sintering ( SLS), and Solid Lamination (SLA), please refer to the following:
[3D Printing Knowledge] Application Guide to Creating Thermoforming Templates using SLA 3D Printing
[3D Printing Knowledge] Application Guide to Creating Thermoforming Templates with SLS 3D Printing
[3D Printing Knowledge] Application Guide to Creating Thermoforming Templates in FDM 3D Printing
This article applies to the following compression molding machine: Mayku Multiplier benchtop compression molding machine.
[Key Points at a Glance]
► Spacing between multiple templates
►Male Template & Female Template
►Avoid tightening at internal right angles
The general principle is to avoid recessed areas. If you create a model with beams or recesses, the object cannot be removed after the plastic sheet cools. However, with Mayku EVA Sheets, you can create templates with smaller recesses and raised text on 3D walls.
Recommended recesses when designing thermoforming templates
If your design requires recessed sections, consider creating a template consisting of multiple slotted sections to help release the molded portion.
The tilt angle is the angle applied to the model surface, making it easier to release the template from the plastic sheet. A higher tilt angle makes it easier to remove portions from the template and achieve uniform thickness. Specifically, we recommend using a minimum tilt angle of 5° for optimal molding and template release.
The stepped structure on the laser cutting template is used to compensate for the lack of tilt angle.
Techniques such as 3D printing or CNC milling are suitable for manufacturing templates with angled surfaces. However, angled surfaces cannot be used when employing manufacturing methods such as laser cutting. In these cases, you can add "steps," a ramp consisting of multiple small steps, instead of a single large three-dimensional wall.
Laser-cut templates are used to compensate for the lack of tilt angles in stepped designs.
Width is easier to shape than height, so when designing a model, the width must be greater than the height, or a slight tilt angle can be used to compensate.
Thermoforming template design: width and height
Some template designs create air pockets or indentations during the molding process. By adding ventilation holes to these indentations, air can escape during molding, allowing for the hot pressing of more detailed sections.
The more ventilation holes a thermoforming template has, the more detailed parts or molds it can create, and the less likely it is to form air bubbles.
The higher the final quality, the better. If you value producing models with exquisite surface text and texture details, this step is absolutely essential and cannot be omitted.
Thermoforming template design: using ventilation holes to capture details
We recommend using tapered ventilation holes.
The number of ventilation holes depends on the template design and they are placed near the edges and corners of the recessed areas .
The size should also be moderate, with a diameter not exceeding 0.5mm, so that it is not easily noticed in the final part; if the ventilation hole is too large and the sheet used is thin, the sheet may bounce off during the molding process, resulting in molding failure.
Thermoforming template design: Use ventilation holes to prevent air bubbles
Here are some technical recommendations regarding the size and shape of ventilation openings:
SLA 3D printing: 0.5mm diameter tapered ventilation holes.
FDM 3D printing: 0.5mm diameter tapered ventilation holes. A higher printing resolution than 0.5mm may be required.
SLS 3D printing: For certain porous materials, such as nylon and certain polyurethane sheets, ventilation holes are not required due to the porosity of the template.
Conical ventilation holes on thermoforming template
The size and shape of the vents are important considerations when using SLA 3D printing and FDM 3D printing, as resin can easily become trapped or filler can accumulate in small vents, causing printing problems.
Location of ventilation holes on automotive parts template
Depth of depression
When plastic sheets are molded into three-dimensional shapes, their surface area increases and they become thinner. Different shapes and features of stencils will result in different sheet proportions. For example, if a stencil doubles the surface area of a plastic sheet, its average thickness will be halved, so the final thickness is often inconsistent.
If your template has recesses, ensure that the depth of the recess does not exceed two-thirds of the width of its surface opening . Larger recesses significantly increase the risk of thinning of the final surface area.
Thermoforming template design: Recess depth
Thermoforming is not suitable for molds with sharp angles (less than 90°) . Besides the smallest possible tilt angle, sharp vertical angles are more likely to cause mesh-like tearing of the plastic sheet during molding. To avoid this and improve part quality, ensure that all corners and edges of the mold are rounded.
Thermoforming template design: Sharp corners
During thermoforming, the heated sheet gradually adapts to the template and is fixed in place as it cools. As the material approaches a corner, it thins out.
To ensure consistent section thickness and improve structural strength, round off corners and edges. Corner radii contribute to consistent material flow.
Comparison of material thickness at acute and rounded corners
Even if the texture on the printed part is not obvious, the thermoformed part will replicate the surface texture of the part, so this should be kept in mind during the design process. If a smooth surface effect is required, the part may need to be pre-treated.
Surface textures generated when using SLA 3D printing templates
The amount of post-processing required will vary depending on the technology used to create the template. For example, when using FDM 3D printing, more layers are typically pressed out than when using SLA 3D printing.
The Mayku Multiplier can be used to manufacture parts with a minimum resolution of one micrometer.
In these cases, even if created using SLA 3D printing, only light sanding of the final part is needed to achieve the desired surface finish.
Surface texture generated when using FDM 3D printing thermoforming templates
Spacing between multiple templates
Placing multiple templates too close together can cause a mesh-like structure to form during thermoforming. To avoid this, the spacing between them must be greater than the height of the tallest template .
The thermoforming template is placed in the forming area at the recommended distance.
This rule primarily applies to male molds, where the mesh negatively impacts the final part. However, the impact on female molds is smaller because the mesh does not affect the final part, which is located internally. In the image below, you can see some mesh appearing on the left side of the formed part, but this does not affect the final part inside.
The plastic sheet formed on the Mayku Multiplier shows a mesh pattern on the left side.
Male template & female template
Whether a male or female template is used in pressure forming depends on the part being formed. The dimensions of the material side in contact with the tool surface are most consistent. To ensure a precise fit, the material side in contact with the template is defined.
In the example below, green indicates that the side of the sheet that contacts the template has high detail.
Male template (left) and female template (right)
Avoid tightening at right angles inside.
Cooling can cause the edges to release, but it can also cause the inner parts to lock in. To avoid this, consider adding a tilt angle to features that may tighten during cooling.
The direction of contraction during the cooling process (black arrow = partial release, red arrow = partial tightening).
It is important to know the maximum platen volume that each pressure molding machine can use. For example, the maximum platen volume of the Mayku Multiplier is approximately 3.5 liters (because the pressure chamber is conical).
Maximum template volume (400mm in diameter) compatible with Mayku Multiplier
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