Application Review: Vacuum Forming

Process:
Vacuum Forming

Applicable Industries:
Toys, Appliances, Packaging, Consumer Products, Medical, Sports Equipment, Automotive, Sign Manufacturers & Aerospace

Types of Masters Used:
CNC or Conventionally Machined Patterns
LOM (Laminated Object Manufacturing)
SLA (Stereolithography Apparatus)

Types of Molds Used & Number of Parts:
Machined Wooden Patterns 200+
Machined Aluminum Mold Production Quantities
LOM (Laminated Object Manufacturing) 100+
SLA (Stereolithography Apparatus) 50+
Cast Urethane or Epoxy Tool 500+
Spray Metal Tool 1000+

Procedure:
Vacuum forming is a process in which a thermoplastic sheet is heated to a pliable state and then placed over a mold and drawn into the mold to the desired shape of the finished part. Recent engineering advancements in thermoplastic materials have greatly contributed to the production of parts and prototypes by vacuum forming techniques. Since small volumes do not justify using conventional tooling methods vacuum forming allows a manufacturer to penetrate a small volume market effectively.

The first step in making a vacuum formed part is creating a master pattern to produce the mold. The pattern is positioned as needed and a framework is constructed to shape the outside of the mold. After applying a release agent to the pattern an epoxy can be used to form the mold. A mold constructed on the SLA or LOM machined can be used directly for forming since the temperatures involved in the vacuum forming process are generally less than 130 degrees. The SLA and LOM materials can withstand these temperatures.

Once the mold has set, it is then mounted on a back plate and vacuum holes are drilled through the mold and around the periphery of each pattern. This allows the heated plastic sheet to be pulled completely over the mold to ensure an accurate finished part.

After preparations of the mold have been completed, the manufacturer is ready to perform the vacuum forming process. The plastic sheet is placed over the mold and clamped into place. A vacuum is then applied from beneath the mold and the heated plastic drawn down into the cavity. After the plastic has been allowed to cool, the clamps are taken off and the formed sheets are removed from the mold, then the individual molded parts are cut out and deburred.

Using an SLA or LOM pattern is advantageous in several ways. The lead time as well as the cost, for creating a pattern is greatly reduced. In addition for more complex parts, vacuum holes can be designed directly into the mold pattern. This takes the guesswork out of placing the holes in the mold.

Vacuum forming is used in a variety of different industries. The automotive industry uses vacuum forming to produce automotive trim as well as some interior components. The consumer products industry can make products ranging from plastic glasses to food containers by using the vacuum forming process. On a larger scale, vacuum forming is used to produce many of the signs for gas stations and convenience stores. Vacuum forming is also used in a variety of applications in the aerospace and medical industries. Vacuum forming is widely used in packaging techniques known as blister pack.

Vacuum forming is a very cost effective method for producing small or large quantities of molded plastic parts. By incorporating Rapid Prototypes into the vacuum forming process, parts can be produced on a high quantity basis for a relatively low cost, thus saving the manufacturer both time and money. With the continuing improvement in part accuracy. Rapid Prototyping will continue to be a valuable asset to the manufacturer.