Parts that are tall and/or thin may require changing to a male mold geometry, which presents different challenges.

In both cases, male and female mold geometries, the thinnest wall thickness will be along the vertical side walls and at the bottom of “inside” corners, where the film is stretched the furthest. Conversely, film that touches a more horizontal mold surface first will be more like the starting gauge of the film as it is stretched the least. The engineer, when designing a part for thermoforming, must consider tapering and gauge loss when considering thermoforming as a manufacturing process. As a rule of thumb, the taller the vertical surfaces, the greater the taper in the side walls and the thinner the film will become.

Stress is locked in during that first cooling cycle after being melted, and will be relieved only at the next heating cycle. The stress in any plastic is “heat history sensitive” and will be removed only once during its first excursion back to the temperature at which it was locked in. Note that these stresses may be locked into the plastic across a range of temperature, and to remove all of it requires that it be heated back to those temperatures. Generally, it’s sufficient to revisit a temperature only somewhat higher than will be experienced in an application to stabilize the part.

Thereafter, the only expansion and contraction that will occur at that (relieved) temperature with be the typical amount for that plastic’s normal physical properties, i.e., coefficient of thermal expansion. Axial and bi-axially oriented films have huge amounts of stress built as a benefit, as with film to “shrink” package your items (like frozen Pizza) or shrink package your boat for the winter to keep the weather out.

From the press release:

“High-performance batteries enhance the quality of life of pacemaker patients substantially. Because of space restrictions in pacemakers, battery insulators must be precisely tailored and as thin-walled as possible. To produce this protective liner, Welch Fluorocarbon, a company based in Dover, New Hampshire, USA, has now developed a unique process using a VESTAKEEP® polyetheretherketone (PEEK) film from Evonik Industries.

Earlier generations of pacemakers were fitted with batteries that had to be recharged daily. Only with the advent of high-performance batteries, however, were patients relieved of this considerable burden. Following a period when even plutonium-based radionuclide batteries were used, pacemakers are now fitted almost exclusively with top-capacity lithium iodine batteries, which power the pacemaker for up to ten years. These must be accommodated in the confined spaced of the pacemaker. The space available for the insulation is also very limited, and wall thickness tolerances are low. For this reason, the batteries have so far been encapsulated manually with considerable effort using polyimide adhesive strips or parylene conformal coatings.

Custom-fit insulators are an alternative, but they usually cannot be produced by injection molding because of their thin wall thicknesses, low tolerances, and long flow paths. The company Welch Fluorocarbon has now developed a unique thermoforming process that makes it possible to manufacture such components. A plastic film is fixed in a frame, melted completely by heating to a temperature above the crystalline melt point of 340 °C, and then molded in vacuum. This molding from the melt produces particularly low-stress molded parts.

Because the insulator material must be chemically resistant to metallic lithium, the choice of suitable polymers is rather restricted. Welch decided on an amorphous VESTAKEEP^® PEEK film from Evonik, which both companies developed in close collaboration. The film is unusually low-stress and, in contrast to conventional extruded films, hardly flows at all on melting. Only in this way is it possible to comply with the low thickness tolerances required. Using this film, Welch Fluorocarbon is now producing battery insulators with wall thicknesses of less than 25 microns and at extremely low tolerances.

VESTAKEEP^® film is highly resistant to chemicals and also features very high mechanical and flame resistance; it is stable even at high continuous working temperatures, and has excellent tribological and electrical properties. Evonik offers suitably adapted crystalline and amorphous VESTAKEEP^® films for all sectors of industry, including medical applications.”

Please contact us to learn more about our Thermoformed PEEK components.

Here is an excerpt from the article:

“Thin-wall thermoformed parts are taking aim at injection molded parts for critical electronic and medical applications.

A New Hampshire company is using old-fashioned Yankee ingenuity to form materials at or above their crystalline melt temperatures to manufacturethree-dimensional parts with stress- and pinhole-free thermoplastic walls. Parts with super thin walls are in demand for applications where real estate is at a premium, such as implantable medical devices and miniature electronics. Typically, the parts protect components against chemicals or act as electrical insulators.

“Sometimes companies can’t injection mold parts with some high-performance thermoplastics because they can’t get the materials as consistently thin as required,” says Scott Behner, sales team leader at Welch Fluorocarbons in Dover, NH. “They don’t have the ability of making a wall that is 1.0 mil (one thousandth of an inch) thick.” Another issue is that very thin injection molded walls may have weak spots caused by weld lines, resin impurities, or stresses created by high pressures. Limitations on wall thickness for injection molding vary widely, and are dependent on part design, melt flow characteristics of the resin, and robustness of the molding machine.”

To read the entire article please visit Design News, and please contact our Sales Team for further information regrading our Thermoforming of high-performance thin films.