A twin-sheet thermoformed pallet uses PP foam as a plug assist that becomes the lightweight structural core. This processing and design innovation was unveiled at the recent 14th Annual SPE Thermoforming Conference in Indianapolis. Machinery developments included a new high-speed, in-line thermoformer and a form-trim-and-stack unit for short runs. Other advances were a prototype machine for material characterization and a new version of thermoforming simulation software.
Foam plays dual role The twin-sheet Air Ride Pallet, developed by Novo Foam Products LLC, Findlay, Ohio, combines TPO outer skins with a lightweight and resilient foam core of expanded PP beads. This is reportedly the only lightweight pallet with a flat deck that is reusable. Other pallets made of high-impact PS have a flat deck but are for single use, says Tom Bohan, managing partner of Novo Foam, a technology development and product-design firm.
A key element of the innovative process is the steam-chest-molded EPP foam, which serves initially as a plug assist. In contact with the hot TPO sheet, the beads are compressed, producing a strong bond between the PP-based foam and sheet. The result is an I-beam structural panel produced in one step without adhesives. The top sheet is 0.06-in. thick, the bottom sheet 0.08 in., and the core has 1.9 pcf density. The manufacturing process, which utilizes a Brown rotary thermoformer, has a 2-minute cycle.
Bohan declined to elaborate further on the process but said it includes special control software that sequences machine operations. The pallet measures 48 x 40 x 5.5 in. and weighs 13 lb. Novo Foam is aiming it at food and pharmaceutical applications, among others. The pallet is being contract manufactured with a start-up volume of 10,000/month. Bohan said potential volumes could reach 100,000/month. Novo Foam is actively seeking licensing and joint-development opportunities in various industries, including automotive, where there is said to be strong interest.
Accuform in the Czech Republic announced a new version of its T-SIM thermoforming simulation software, available from Compuplast North America. T-SIM 4.5 for Windows XP offers new features and provides more integration with finite-element stress-analysis systems like Ansys and LS-Dyna. It also has a new mapping function for part thickness. Now thickness values can be mapped directly onto a stress-analysis model for more accurate prediction of mechanical performance. The new version also allows specifying zone temperatures instead of a uniform sheet temperature to create a desired thickness profile, says Compuplast president John Perdikoulias. The new version also predicts image distortion for in-mold decoration, minimizing trial-and-error.
A key development that could help spread acceptance of thermoforming simulation is a prototype testing machine for material characterization developed by the Institute for Polymer Testing and Polymer Science at the University of Stutt gart, Germany. Simulation software requires accurate materials data in order to make accurate predictions. But until now, precise data on materials behavior under thermoforming process conditions has been unavailable because testing procedures have been too costly and time-consuming, says David Liebing, a lead engineer at the Institute.
The Institute partnered with Accuform and German thermoformers Wagner GmbH and Jacob Kunst stofftechnik to develop a testing apparatus for materials such as PS, PP, PET, and PVC. The prototype machine, priced around $25,000, provides a quicker and less costly method to characterize materials, Liebing says. It can also be used to compare new materials with a reference material for quality assurance. The joint development group is looking for a company to produce a commercial version of the device.
In new machinery, Illig introduced a high-speed, in-line, cut-in-place pressure former for cups, the RDM 78K. Aimed at the U.S. market, the 30 x 17 in. machine runs PP cups in 45 cavities at 37 cycles/min, producing about 100,000 cups/hr. Four separate cooling circuits reportedly provide more efficient cooling and quick-response air valves speed forming in the tool. The RDM 78K also provides a one-hour tool change and a flexible stacking system for a range of cup designs.
According to Illig general manager Stefan Deuschle, a relatively narrow sheet width of 32 in. helps avoid sag and unequal cup weights. Illig cites tolerance ranges of 4.7 to 4.9 g for cup weights, 0.0362 to 0.0381 in. for sealing rim thickness, and 2.833 to 2.835 in. for cup height. Such tight tolerances reduce material usage and optimize downstream equipment performance, according to Deuschle.
Also new is the RFT Custom machine from Lyle Industries. This form-trim-and-stack unit provides flexibility for short and long runs, while also offering heavy-duty specs. Brian Crawford, v.p. of sales, says the company is expanding efforts in shorter-run applications in markets such as packaging. He calls the RFT Custom a “more focused” machine for blister packs and clamshells made of PVC, PS, and PETG.
The machine’s four oversized platen-guide posts allow for higher forming pressure (60 tons), and the tubular chain rails also are stronger and allow for more precise temperature control, according to Lyle. The machine has a dancer unwind station, 110-in. oven, 32 x 36 in. mold capacity, and 100-ton trim station and scrap winder. The forming unit comes with an optional quick-change tooling package that permits changeovers in 15 min.
Among the innovations displayed in the parts competition was what was said to be the first twin-sheet part with a decorative paint film. The running board for the 2004 Chevrolet SSR pickup truck is also claimed to be the first paint-film decorated part formed in a female tool, according to thermoformer Durakon Industries of Lapeer, Mich. Previously, all thermoformed paint-film parts, such as trim applications and rocker covers, had been manufactured in male tools to maintain gloss requirements.
In twin-sheet forming, the paint film contacts the mold surface, so Durakon utilized proprietary techniques, some of them involving mold finish, to maintain high gloss, according to Les Smith, senior technical specialist. The sheet is coextruded of TPO and glass-filled PP, and the paint film is a PVDF from Avery Dennison. The paint film is laminated onto the sheet and then two sheets, one with the laminate and one without, are run through the thermoformer. The resulting 9-lb running board is robotically trimmed and finished.
Typically, running boards have consisted of a decorative TPO part that is injection molded and mounted on a steel frame and then painted. The twin-sheet part is more scratch- and chip-resistant, weighs 30% less, and eliminates corrosion, Durakon claims.