A Guide to Thermoforming Heavy-Gage, Complex Parts: From Material Selection to Custom Tooling

In many instances, thermoforming of heavy-gauge plastics (thicknesses of 1.5 mm/.060 in. or greater) is the technology of choice for manufacturers and new product designers. Using this process of vacuum forming heated plastic sheets is ideal for many products and components required by medical device manufacturing and countless other industries.

A wide variety of heavy-gauge plastic materials are available for this process, many of which can be used for complex parts that demand tight tolerances, intricate geometries and special properties such as fire resistance.

At the same time, thermoforming tooling and prototypes are often developed more quickly than many conventional molding methods and can be performed through a number of economical processes. (See Figure 1)

These same attributes may also be the source of confusion, wheel spinning, and the expenditure of unnecessary costs if customers are too self-reliant when they design parts for the heavy-gauge thermoforming process. What is often needed is a collaborative process that includes thermoforming specialists early in the design of the products that will be formed.

Get Design Support Early

Jesse Hahne, a highly experienced design engineer at the Center for Advanced Design (CAD), Elk River, MN, found that it is highly beneficial for the customer’s design engineers to collaborate with their thermoforming vendor early in the process. He says that the vendor can help validate the geometry and features of the product design, confirm or assist with material selection, determine how tooling should be developed, provide prototypes quickly, and economically, and, of course, confirm the best process for meeting production volume requirements.

CAD is a design firm that focuses on the plastics industry, including design for vacuum forming, rotational molding, injection molding and blow molding. Hahne consults with many in-house engineers of clients as well as with thermoforming specialists and the molders of different plastic forming technologies.

Confirm the Process

In some cases, requests to evaluate the use of thermoforming a product might best be produced by another process.

It is vital to get support from a supplier’s technical staff early in a project, especially if they are familiar with various forming and molding technologies. This can be very valuable in helping the customer validate that they are considering the right process.

It’s beneficial to find a vendor that offers a variety of techniques, including pressure forming of heavy-gauge plastics, which is often times a suitable process. Pressure forming is similar to the vacuum forming process, but with specific tooling can produce parts with much greater definition. In instances where volumes are relatively low, pressure forming may be a viable alternative to much more expensive injection molding.

With both thermoforming and pressure forming projects, a vendor can assist customers from design to materials selection, tool development, prototyping or 3D modeling and production.

Check Tooling Specifications

It is often vital that design engineers validate tooling with thermoforming specialists, particularly when the project includes design complexities. These could include such requirements as undercuts, the use of breakaway molds, two-piece products involving manifolds or ductwork, or products that require special trimming or surface finishes.

Forming complexities can be problematic for some thermoforming shops. They are often achievable, but may require modifications in tooling that could result in cost savings. (See Figure 2)

With thermoforming you have much greater flexibility with tooling than you have with technologies such as blow molding or rotational molding. For example, for smaller projects you can 3D print and test the tool. If a large tool is required, then you build a wood pattern and produce test parts from it, then make changes to the pattern before you finalize the tool design.

That tooling flexibility of the thermoforming process enables the right vendor to work with a wide range of sizes, using plastic materials from .010" to .450" thick to produce parts as large as 5 feet x 8 feet, with a maximum draw or depth of 30", with draw ratios to select the proper base thickness and forming process.

Validate Material Selection

While a wide variety of plastic materials are appropriate for thermoforming, it is wise to work with thermoforming specialists to determine the availability of materials, volume requirements, and the ability of materials to meet design requirements. (See Figure 3)

Materials such as acrylonitrile butadiene styrene (ABS) and polyethelenes are suitable for many projects, but others require more demanding properties that are available with more advanced materials including thermoplastic polyolefins (TPOs), polycarbonate, and Kydex®.

Any of a number of factors could come into play when companies are considering material selection for products or components. Those could include the finish, impact resistance, fire resistance or scratch resistance and many others.

These advanced materials have properties that are excellent for many specific applications, for example, polycarbonate when a tough, transparent product is needed; TPOs for stability; Kydex for its cleanability so that scuffs and scratches may be removed from the surface of the material, as well as its excellent chemical and flame retardant properties.

However, some of these materials may not be practical or even available for low-volume projects. In those cases, secondary processes may become part of the solution, whether painting or silk-screening or other cosmetic solutions. That’s one of the reasons why it’s important to consult with an experienced thermoforming vendor about material selection early in the design process.

Start-to-Finish Feedback

Several years ago Kent Olson, vice president of Packaging Plus, Inc., Rogers, MN, had a special project for a large medical company that required heavy-gauge thermoforming. Olson worked with Alpha Plastics, Coon Rapids, MN, on the project. The product was a tray composed of R-63, a black, conductive material that is static dissipative that would be used in a clean room.

The tray was a unique design and the tolerances needed to be very precise, within thousandths of the medical company’s requirements.

The company has required additional sizes of the medical trays over the years, as well as a catch basin project that required a fairly deep draw of approximately 12 inches.

Olson soon learned that working with a good thermoforming vendor involves a highly comprehensive process. At the beginning of the project the vendor should meet with the company’s technicians and go through the specific requirements. They then should provide the necessary drawings, and after review, should create a prototype for the customer. After that is approved, it should then go into production. It is very significant that the chosen vendor keep the customer informed all along the way. That is one of the keys to design success.

This article was written by Jeff Walczak, Executive Vice President, Alpha Plastics, Inc., Coon Rapids, MN. For more information, Click Here .

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