Vacuum forming stands as a cornerstone in the realm of manufacturing processes, celebrated for its simplicity and versatility. By heating a plastic sheet to a pliable state and then conforming it to a mold with vacuum pressure, manufacturers can produce parts that are both resilient and functional. This process is not only cost-effective but also adaptable, making it a preferred choice across diverse industries such as packaging, automotive, medical devices, and consumer goods. The ability to create intricate and high-quality parts with minimal tooling expenses makes vacuum forming an attractive option for both prototyping and large-scale production. However, to harness its full potential, meticulous design considerations are imperative to ensure that the end product meets high standards of strength, precision, and aesthetics.

Key Design Principles for Vacuum Forming

1. Use Draft Angles for Easy Mold Release

Draft angles are integral to the vacuum forming process, facilitating the smooth removal of the formed part from the mold. These angles are slight inclinations added to the vertical walls of the mold, ensuring that the plastic does not adhere too tightly. Without draft angles, the risk of damaging the part during demolding increases significantly. Typically, a draft angle of 3-5 degrees suffices for most applications, but more complex molds may necessitate larger angles. Technologies such as 3D printing and CNC milling can easily incorporate draft angles, while methods like laser cutting may require alternative approaches, such as using inclined planes divided into steps.

2. Minimize Undercuts

Undercuts present a challenge in vacuum forming as they can impede the easy removal of the part from the mold. These features may require more complex multi-part molds or additional tooling, increasing production costs and time. To streamline the process and reduce expenses, it is advisable to minimize or eliminate undercuts. If your design necessitates undercuts, consider using a template composed of multiple slotting parts to facilitate part release.

3. Control Width-to-Height Ratio

The width-to-height ratio, also known as the draw ratio, is critical in ensuring the quality of the formed part. An improper ratio can lead to material tearing, deformation, or difficulty in demolding. Generally, the height should not exceed 2 to 3 times the width to prevent excessive thinning. This ratio must be adjusted based on the material's properties, as different plastics exhibit varying levels of stretchability. For instance, materials like PET, HIPS, and ABS can be moderately deep-drawn, while more flexible materials like LDPE and PVC allow for greater depth.

4. Optimize Air Flow with Air Holes

Airflow optimization is crucial for achieving high-quality, detailed parts in vacuum forming. Air holes strategically placed in the mold help evacuate trapped air, preventing bubbles, distortions, and incomplete formations. These holes should be small and discreet, ideally with a diameter of 0.02 inches, to remain inconspicuous on the final part while effectively releasing trapped air. Overusing air holes can weaken the mold or leave unwanted marks, so focus on strategic placement near problem areas.

5. Cavity Depth Considerations

When a plastic sheet is molded into a 3D shape, its surface area increases while its thickness decreases. The cavity depth in the forming template should not exceed two-thirds of the width of its surface opening to prevent overly thin surfaces. Exceeding this ratio can compromise the quality and durability of the final part.

6. Avoid Sharp Angles

Sharp angles, particularly those smaller than 90 degrees, pose a risk of tearing during the vacuum forming process. To mitigate this risk, ensure that all corners and edges are rounded. A recommended fillet radius of at least 3–5 mm, depending on the material, helps prevent excessive stretching and stress concentration, enhancing the quality and durability of the part.

7. Consider Corner Radius and Material Flow

As the heated sheet material conforms to the template, it tends to thin out around corners. To maintain consistent thickness and improve structural integrity, rounding off corners and edges is essential. A rounded corner radius ensures smooth material flow, reducing the risk of weak or inconsistent areas in the final part.

8. Surface Texture and Template Placement

The surface texture of the thermoformed part replicates that of the template. If a smooth finish is desired, post-processing may be necessary, especially when using technologies like FDM 3D printing, which can leave noticeable layer lines. Template placement is also crucial to prevent webbing, particularly in male molds. Ensuring a gap larger than the height of the tallest feature in the template helps avoid this issue.

9. Male vs Female Templates

In vacuum forming, the choice between male and female templates depends on the part being produced. Male templates feature convex shapes, while female templates have concave shapes. The side of the material that contacts the tool-face is the most dimensionally consistent, so defining the part based on the side that will touch the template is important. MY YARD's all-in-one desktop vacuum formers accommodate both male and female templates, providing flexibility for different forming needs.

10. Design for Shrinkage

During the cooling process, edges may release, but internal parts can become trapped. To prevent this, incorporate draft angles into design features at risk of being locked during cooling. MY YARD FORMART 2's built-in directional valve automatically blows cooling air after vacuum forming, aiding in part release and reducing the risk of warping or damage during demolding.

Choosing the Right Vacuum Former

Selecting the appropriate vacuum forming machine is crucial for achieving high-quality results. MY YARD offers comprehensive, all-in-one desktop vacuum formers suitable for both beginners and professionals. These machines feature a built-in vacuum pump, eliminating the need for an external pump, and a user-friendly interface with a built-in materials database. The MY YARD FORMART 2 model offers advanced capabilities, such as auto-mold releasing and a built-in directional valve for easier mold release. By exploring detailed specifications and compatible materials, you can find the best machine for your specific needs.

By combining proper design techniques with advanced thermoforming technology, you can achieve consistent, high-quality results with minimal effort.