Learn More About Thermoforming

Thermoforming is the process by which three dimensional plastic parts are shaped from a softened thermoplastic sheet. The process involves heating a plastic sheet to a temperature range where it is soft, and then stretching it against a cool mold surface. When the sheet has cooled to the point where it retains the shape of the mold, the sheet is removed from the mold and excess plastic trimmed from the part.

The first step in making a vacuum formed part is fabricating the forming mold or tool. Vacuum forming molds can be made from a variety of materials ranging from wood to steel and can be single cavity or multi cavity. Once produced, the tool needs to be vented so that all inside corners have a way to evacuate air once the softened sheet is pulled over the mold. Proper venting is critical to ensure that the plastic sheet is pulled completely against the tool.

custom thermoforming product advantages and disadvantages

The vacuum forming process itself is broken down into the following steps:

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Film is moved into position over the mold in either sheet form or roll form
Film is clamped in place in a frame that holds the edges of the sheet
Film is heated until softened
Mold is introduced into the softened sheet and vacuum is applied
Film is allowed to cool while still on the mold
Formed sheet is removed from clamping frame
Parts are rough trimmed from larger sheet
Parts are final trimmed
Inspect and Package

Thermoforming has certain advantages over other methods of producing plastic parts:

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Low tooling cost relative to injection molding
Prototype speed (Prototype tools are typically less involved than with other methods)
Parts with very small thickness to area ratios can be fabricated
Extremely large parts can be fabricated

Disadvantages of Thermoforming:

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High part cost relative to injection molded parts
Non-uniform gauge due to film stretching
Process is limited by geometry. Typically parts with undercuts are not achievable

Common Thermoforming terms Defined:

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Thermoforming: Generic term used to describe forming parts from a softened plastic sheet.

‍Vacuum Forming: Term used to describe forming into a female mold

‍Drape Forming: Term used to describe forming over a male mold

‍Webbing: A phenomenon that occurs when the area of the melted sheet is larger than the mold’s ability to capture it. The result is excess film that folds onto itself creating “Webs”

‍Thermoforming window: The thermal range in which the particular polymer can be stretched and formed.

Mold Design:

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A common question is: “When do I choose a male mold or female mold when designing my parts?” The general rule of thumb is:

Select Male Mold when:

Making tall parts
Better part definition is required
When you want thicker bottom (or top, if part is inverted) and thinner side walls

Select Female Mold when:

Making shallow parts
Side walls must be thicker and bottom thin
Female mulitcavity tools fit more parts / unit area
Definition is not required