Thermoforming

Vacuum forming tools used for prototyping can be made from a variety of materials. The material choice will depend on the application and varies in cost. At Kal Plastics, we use wood for prototyping as much as possible because it is the least expensive material. 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. 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. 3D printed tools and ceramic tooling and fixtures are also available as an inexpensive option for customers with low volume production requirements.

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

• High Density Polyethylene (HDPE)
• Low Density Polyethylene (LDPE)
• Engineered Polypropylene (TPO)
• Polycarbonate (PC)
• High Impact Polystyrene (HIPS)
• Acrylonitrile Butadiene Styrene (ABS)
• ABS Chrome and Paint Film (ABS)
• Polyvinyl Chloride (PVC)
• Copolyester (PETG, Glycol-modified Polyethylene Terephthalate)

There are a few inherent guidelines to vacuum forming that must be followed:

Vacuum forming is more of an art than a science. No two jobs are alike, and every part presents its own unique set of challenges. There are many “tricks of the trade” to consider when approaching a new project, so it sometimes takes time to get a part right.

Mold design undercuts are not desirable and require special mold inserts which tend to greatly inflate 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 do not require a draft if the mold is smooth and one-half degree if textured. Ideally, parts should also have the same general cross section.

The most common limitation is part depth when utilizing a female mold. As a rule, the depth of a part cannot exceed 75% of the width or length- whichever is less. 

Lead times vary depending on the project. Custom or first-time jobs take longer than simple or repeat projects. When new tooling is required, four to six weeks is the average turnaround time for delivery of a first article. Production parts then follow two or three weeks after the first article approval. The standard lead time for custom orders not requiring new tooling is from one to six weeks, depending on the type of material to be used. 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 project is a unique puzzle to be solved and has its own special recipe for success.