Questions About the Thermoforming Process? 

We are sure you might have some questions regarding the thermoforming process.  Some of the most commonly asked questions have been answered below.  However, we would love the opportunity to answer any additional questions you might have regarding thermoforming your custom plastics product.  For additional information, check out our Thermoforming Design Guidelines, or contact us now!

vacuum molding-vacuum forming

Thermoforming is a generic term for the thermoforming process of producing plastic parts from a flat sheet of plastic under temperature and pressure. In the highest expression of the technology, thermoforming offers close tolerances, tight specifications, and sharp detail. When combined with advanced finishing techniques, high-technology thermoforming results in products comparable to those formed by injection molding. All of us are exposed to many thermoformed plastics in our daily lives. They have replaced many parts previously manufactured from wood, paper, glass, and metal.

Thermoforming is efficient and very cost-effective for the production of many plastic parts depending on their size, shape, and quantity. Initial project costs are usually much lower, and lead times to tooling and production are generally much shorter than other processes. Modifications to design often times may be achieved. Temporary tooling offers an inexpensive short-term test for design issues and product market acceptance.

Large panels, housings, enclosures, and similar parts are especially well-suited to the thermoforming process. One of the benefits of thermoforming is lower tooling costs. Tooling costs for these parts are considerably less than injection molding, which can be cost-prohibitive. Parts with features mostly confined to one side of the part are best suited to thermoforming. However, features on the uncontrolled side of the part may be addressed by trimming or fabrication and assembly.

The following table list our standard tolerances:

Typical Thermoform & Pressure Form Tolerances
Download a PDF of this file.Formed Features

Formed FeaturesPressure-formingVacuum forming
Less than 6″+/-.010″+/-.015
6″ to 12″+/-.020″+/-.025″
12″ to 18″+/-.025″+/-.030″
Above 18″, add+/-.002″ per inch 

CNC Trimmed Features

Machined features from a formed surface+/-.015
“Hole to Hole”+/-.010
Hole Diameter+/-.005

The side of the plastic formed against the mold can be controlled with close tolerances. While the side away from the mold cannot be controlled,  we are able to predict what will occur on the uncontrolled side. Tolerance requirements on the uncontrolled side are addressed by trimming or fabrication and assembly.

We typically deal with materials ranging in thickness from .040″ to .500″.

Plastics that lend themselves best to thermoforming are: acrylonitrile-butadiene-styrene copolymer (ABS), high-impact polystyrene (HIPS), high density polyethylene (HDPE), high molecular weight polyethylene (HMWPE), polypropylene (PP), polyvinyl chloride (PVC), polymethyl methacrylate (or “acrylic”) (PMMA), and polyethylene terephthalate modified with CHDM (PETG).

Sharp, crisp detail with close tolerances can be achieved using a thermoforming process. Undercuts, formed-in texture, formed-in logos, formed-in hardware, and custom colors are just a few of the many features that can be accomplished with thermoforming. This subject is covered in more detail on our design considerations page.

Twin Sheet forming is accomplished by simultaneously forming two separate sheets in their respective separate molds to create hollow and double-walled parts comparable to roto-molded parts but with much more detail and better cosmetics.

A vacuum fixture is required when a part must be CNC trimmed. Vacuum fixtures are constructed by taking a reverse impression of the part and mounting this impression into a vacuum box. The trim fixture then holds, under vacuum pressure, each part being CNC trimmed to ensure consistent results. Other tooling specifically required in the forming, trimming, fabrication, and assembly of each part is designed by ATI engineers and constructed by the ATI tooling department.

Machined Aluminum Molds
Machined aluminum molds are typically built for shallow parts with small draw ratios. ATI uses 6061-T6 aluminum for the construction of these molds, which can be held to very close tolerances. These molds are then mounted on a temperature control base to control the mold temperature during the forming process. Male or female molds and vacuum-form or pressure-form molds can be machined aluminum molds. They can be textured and may offer features such as loose cores, pneumatic cores, and inserts.

Cast Aluminum Molds
Cast aluminum molds are cast at a foundry from a pattern machined by ATI from a composite material. The temperature controls are cast into the back and sides of the molds at the foundry. Cast aluminum molds typically are built for parts with large draw ratios and may be male or female and vacuum-form or pressure-form. Features such as texture, loose and pneumatic cores, and inserts are available.

Composite Molds
For prototyping and short production runs, cost-efficient composite materials are used for mold construction. These molds produce parts that are to be evaluated for fit, form, and function and may be modified to evaluate possible design changes. These molds are for vacuum-forming only and are not temperature controlled. These molds have a limited life.