Vacuum Forming 101

Vacuum Forming, also known as Thermo Forming is the process of forming a heated sheet of a thermoplastic over, or into, a mold which is then allowed to cool to form the desired part. The process becomes vacuum forming when the mold itself is drilled with vent (vacuum) holes and is connected to a vacuum to evacuate the remaining trapped air.

Each mold is connected to a vacuum box so that when the heated thermoplastic sheet touches the mold, the vacuum is activated and the air pressure pulls the plastic tightly to the mold for detailed forming.

Vacuum forming offers processing advantages over competitive processes such as fabrication, blow molding, injection blow molding, rotational molding, and injection molding. Because tooling costs are lower, relatively large parts can be economically fabricated. Vacuum forming is also ideal for prototyping and product development due to the lower tooling costs and faster turn around. In many instances, a vacuum formed part is of higher quality and will last longer than an identical part made by a different process. This is especially true when comparing an injected molded part to the same part, vacuum formed. Vacuum forming is also ideal for any part not expected to exceed a volume of 50,000 or more.

Vacuum forming tools used for prototyping can be made from a variety of materials. The material choice will depend on the application and will vary in cost. At Kal Plastics, we use wood for prototyping as much as possible because it is the least expensive. However, wood does have some limitations and cannot be used in every application.

Production tools are typically made from machined or cast aluminum which are temperature controlled and last indefinitely. In terms of cost, an aluminum tool is much more expensive than a wood prototype mold and sometimes only slightly more expensive than an epoxy prototype mold. As a rule, the more detailed the part, the more expensive the tool.

Kal Plastics has been manufacturing high quality vacuum formed products for over 45 years. We have (8) three and four station, sheet fed, rotary machines for higher volume production, and (4) sheet fed, single /shuttle station s devoted to prototyping and short runs. Our broad range of equipment allows us to form parts up to 12 ft. by 10 ft. and as deep as3 ft. Kal Plastics is also proud of the fact that we work with recycled and reprocessed materials whenever possible.

Kal Plastics is well equipped to offer a variety of secondary and specialty services. The following is an example of some of the extra services we currently offer:

We are always open to new or better ways of doing things.

A mold will either be a male or female, depending on part design or other particular requirements. Male molds are best in situations that require a tight inside dimension or sharp inside detail. Female molds are helpful in achieving sharp outside detail.

There are many different types of materials currently being used in vacuum forming and choosing the right material involves a variety of factors. The following is just a partial list of materials most commonly used at Kal Plastics:

• High Density Polyethylene (HDPE)
• Low Density Polyethylene (LDPE)
• High Impact Polystyrene (HIPS)
• Acrylonitrile Butadiene Styrene (ABS)
• Polyvinyl Chloride (PVC)
• Copolyester (PETG, Glycol-modified Polyethylene Terephthalate)
• Cellulose Acetate Butyrate (CAB)

There are a few inherent guidelines to vacuum forming that must be understood. First of all, vacuum forming is more of an art than it is a science. This means that no two jobs are alike and every part presents its own unique set of challenges to overcome. There are many “tricks of the trade” to be considered when approaching a new job, so sometimes it may take some time to get a part right.

In terms of mold design, undercuts are not desirable and require special mold inserts which tend to greatly effect the tooling costs. A draft is also needed in the mold so parts will pull off. Male molds require a draft ranging from 1½ degrees to 3 degrees, depending on the material. Female molds, on the other hand, usually require no draft if the mold is smooth and ½ degrees if textured. Ideally, parts should also have the same general cross section.

The most common limitation is with regards to part depth when utilizing a female mold. As a rule, the depth of a part cannot exceed 75% of the width or length, which ever is less.

Lead times will vary depending on the type of job. Custom or first time jobs will take the longest. When new tooling is required, four to six weeks is the average turnaround time for delivery of a first article. Production parts would then be two to three weeks following first article approval. The standard lead time for custom orders not requiring new tooling is from one to six weeks, depending on what type of material is required. Stocking programs are available for custom items that allow us to deliver next day.

Experience shows us that tooling adjustments and working out individual forming challenges are the greatest obstacles, when trying to shorten lead times. Each new mold, or new job, is a unique puzzle to solve and has its own special recipe for success.

• Competitive prices
• Quality Assured
• Over 45 Years Of Experience
• Creative
• Dedicated Team Of Employees
• Service Oriented
• Quick Turnaround
• Innovative
• Experience With Specialty Materials
• Work With Recycled Materials Whenever Possible
• Production Oriented and Able To Do Smaller Runs
• Private Labeling

• Formability: Can this part be vacuum formed? i.e.: Are there any undercuts?
• Material Choice: What are the thermoforming properties and possible limitations?
• Anticipated Volume: Will volume exceed 50,000?
• Desired Tolerances: Are required tolerances reasonable?
• Tooling Budgets: Is proper funding available for tooling?
• Flexibility: Are designers and engineers willing to compromise?