Fundamentally, thermoforming works by drawing a hot sheet of thermoplastic down onto a mold. Each draw uses a single sheet. These sheets can be formed into one or multiple parts depending upon the size of the part. Increasing the number of parts created per draw is one of the best ways to decrease the cost per part of thermoformed products.
After the hot thermoplastic has been drawn down over the mold, a vacuum may be used to suck out any air and accurately reproduce the details of the mold. This process is referred to as vacuum forming. Once the part has cooled, any excess plastic from the sheet is trimmed away leaving a finished part. These cuts can occur at the base of the part, along the wall or in any number of custom variations to create features like holes and slots.
Before thermoforming can begin, tooling needs to be made. These molds and trim jigs can be 3D printed, cast, or machined. If the final product is going to be translucent or transparent, the mold may need custom finishing like sanding or polishing in order to achieve optimal surface finish as the finish will pick up on the tool side of theparts. Depending upon the technology and material used, the lifetimes of these molds can range from hundreds of forms to permanent tooling for unlimited forms.
Thermoforming materials like HIPS, PETG and ABS offer a range of mechanical, chemical and aesthetic properties. Thermoformed parts can rigid or flexible; transparent or opaque; and food-safe, heat-resistant, chemical-resistant, or UV-resistant. Below are our most commonly used materials for thermoforming. To get more information about any material, check out the included data sheet for all the specifications.
Medium- to high-cost engineering plastic with high stiffness, impact strength and temperature resistance, plus options for UV and scratch resistance. Often used for glass replacements on phones, TVs, lights or glasses, as well as high-temp applications. Harder to form than most thermoplastics, especially for fine details.
Moderately hard, inexpensive plastic with high chemical resistance. Does not off-gas at high temperatures. Chemical and thermal durability makes it well-suited for chemical-resistant containers. Higher shrink rate than other materials, which lowers tool life and increases variability between parts.
Traditionally, molds for thermoforming have been machined from urethane or aluminum. Now, 3D printing has become an excellent choice to produce tooling for parts smaller than 11” x 15”. 3D printed molds, especially those produced with Multi Jet Fusion printing, significantly lower the cost per part and speed up production time when compared to machined molds. Moreover, they can easily achieve complex shapes like undercuts that would be expensive or impossible to machine.
Ultimately, each technology offers different strengths for the tooling process. Molded tooling, for example, is good for creating multiple long-lasting molds. Machined tooling is a better option for making large molds, and, depending on the material used, can be permanent or semi-permanent. Even among 3D printed molds, there are different ideal applications for each type of 3D printer.
The overall best tooling option for parts smaller than 15”x11”
The cheapest print option
Generally does not require additional finishing for opaque plastics
Create long-lasting tooling or multiples of a tool at a lower price than printing
Requires a 3D printed or machined master mold
Cheaper to reproduce in multiples than 3D printing, easily get high level of finish for polished parts
Absolute cheapest option for medium to large tools for prototyping
Life is less than 50 forms
Poor to average accuracy
The best option for larger, permanent tools where matte surface finish on tool face is acceptable
Average to good accuracy
Used for automated, high-volume production with fast heating and cooling cycles
Good to excellent accuracy
Best surface finish of any mold, needed for high polish on mold side or clear parts