9 Giugno 2011

Thermoformable Composite Panels

Preconsolidated fiber-reinforced thermoplastics offer short cycle times, tailored properties, recyclability and lower cost.

Unlike thermosets, thermoplastics do not crosslink and cure, and therefore may be heated, formed and cooled several times without loss of properties. This distinction has prompted reinforced-thermoplastic materials suppliers to provide customers with premade, preconsolidated sheet stock, which subsequently can be thermoformed into shaped structures.

Thermoforming uses heat and pressure to transform sheet thermoplastics into the desired shape. In simplest terms, the sheet is preheated then transferred to a temperature-controlled mold and conformed to its surface until cooled. There are numerous variations of thermoforming, distinguished primarily by the method used to conform the sheet to the mold.

FORMING A NEW CATEGORY

The advent of thermoformable panels is driving huge growth in the use of reinforced thermoplastics, particularly in the automotive world, where legacy materials, such as steel and aluminum, have predisposed manufacturers to materials with known, predictable properties available in standard thicknesses, which can simply be formed to shape.

Panel products have been developed from reinforced thermoplastic composites on both ends of the property and cost spectrum. On the low-performance, low-cost end, what the industry officially denotes as commodity plastics (e.g., polyamide), were initially modified with various fillers for automotive applications. As automakers sought to reduce vehicle weight, improve safety, reduce noise, add electronics and streamline manufacturing via modular assemblies, they fueled development of lightweight thermoplastics with progressively greater loadings of chopped glass fiber reinforcement (fiber length of 0.25-inch or less) that offered tailoring of properties, better impact and acoustic performance as well as complex shaping capability and flexibility in manufacturing. Recently, development of long fiber-reinforced thermoplastics (LFRTs) — thermoplastics, such as polypropylene, reinforced with increasingly longer glass and natural fibers (to 1.25 inch or more) — and effective methods for processing and molding them have improved performance and stimulated interest in other markets, including rail, bus and marine interiors, sporting goods and consumer products.

On the high-performance, high-cost end, thermoplastic prepregs were developed to replace thermoset prepregs in niche aerospace applications. The resulting unidirectional tapes and semipregs featured continuous glass, aramid or carbon fiber reinforcements combined, early on, with engineering thermoplastics, such as polyethersulphone (PES) and polyetherimide (PEI) matrices and, more recently, with higher performing polyphenylene sulphide (PPS) and polyetherketoneketone (PEKK).

Today, thermoformable panels produced by suppliers on both ends of the cost/performance continuum offer fabricators a lengthy list of processing and performance advantages: fiber/resin ratios and, where applicable, fiber orientation and architecture are the responsibility of the supplier, so fabricators can focus on a smaller set of forming variables. Manufacturing cycles are shorter (typically 2 minutes or less) and finished products have greater toughness and impact resistance than thermoset composites do — not to mention recyclability, both during manufacturing (recycling scrap) and at the end of service life. And thermoplastic reformability offers fabricators secondary forming options, such as forming parts in multiple steps or making corrections in improperly formed parts.

AUTO INTERIOR & UNDERHOOD APPS

Thermoformable panels are making inroads into automotive interiors. One of the main applications is headliners, which have become increasingly complex. Typically quite thin (as small as 1 mm) at the edges to facilitate attachment and load transfer, headliners must be thicker elsewhere to offer increased head impact protection and maximize noise abatement. Additionally, automakers desire to mold a finished component, including aesthetic covering, in a single cycle.

Three different fiberglass-reinforced polypropylene (PP) materials have been developed to meet these challenges. Each has glass content of 55 percent by weight for the standard product and helps fabricators achieve variations in part thickness in a single forming cycle through a phenomenon calledlofting. Lofting is a mechanical process that increases the thickness and reduces the density of the sheet material when it is exposed to heat. During manufacture, a certain percentage of the fiber reinforcement is oriented in the z-direction and then compressed when the sheet in consolidated during manufacture. When heat is applied prior to thermoforming, the compressed z-directional fibers, like coiled springs, are released to loft the softened thermoplastic. Lofting permits the molders to mold a part with selectively varied thickness. Areas requiring high tensile strength are compressed to a thinner profiles with greater density. "To get a thicker section," explains Harri Dittmar, market manager for development composites at Quadrant Plastic Composites (QPC, Lenzburg, Switzerland), "you construct the tool in such a way that it doesn't compact the lofted material as much in the chosen areas." The thicker sections maintain a greater degree of the initial loft, which produces high stiffness and, at lower density, also contributes to more effective acoustic damping. Lofting reduces part weight and overall part cost, and eliminates the multiple production steps required with previous headliner materials.

AcoustiMax, developed by Owens Corning Automotive (Toledo, Ohio), is supplied in a range of weights, and features a scrim on one side and, on the other side, a customer-specified adhesive film used to co-mold the particular cover fabric required by the application. AcoustiMax sheets are slit to widths and cut to lengths, also to customer spec, and then shipped on pallets.

According to Tom Ketcham, product line manager for AcoustiMax, the product achieves superior noise reduction properties from its lofting ability — more than twice its original thickness. For example, a 1,000 g/m2 sheet of AcoustiMax starts out at a thickness of 3 mm to 4 mm (0.12 inch to 0.16 inch), lofts to 10 mm to 11 mm (0.39 inch to 0.43 inch) during preheating at 390°F (199°C), and then is molded at 110°F (43°C) and 70 psi (4.8 bar) to a final thickness of 5 to 6 mm, depending upon the geometry and compaction of the mold.

 

 

Although no AcoustiMax commercial headliner applications are yet in service, several Tier 1 automotive suppliers have completed prototypes and are in the final stages of material selection for specific vehicles. In addition, AcoustiMax is being developed for trunk liners, door modules, seat backs and package trays.

SuperLite is manufactured by Azdel (Shelby, N.C.), a 50/50 joint venture between GE Advanced Materials (Pittsfield, Mass.) and PPG Industries (Pittsburgh, Pa.). SuperLite forms at 375°F to 400°F (191°C to 204°C) and pressures of 30 psi to 45 psi (2 bar to 3 bar), with lofting capability approaching 200 percent. Gordon King, commercial director for Azdel Europe, says the material's light weight and low-pressure formability can reduce traditional headliner system costs by up to 20 percent.

SuperLite is currently used in headliners for 16 different production vehicles, in sunshades for five, as well as the rear parcel shelf for the Honda Accord and Toyota Camry and the back-panel for the Dodge Ram. It also is used in 11 different interior applications on the Ford GT limited-production sports car.

QPC's SymaLITE, can be made with a glass content from 20 to 60 percent and thermoforms at 50 psi (3.5 bar). Greater glass content produces increased lofting — five to six times its original thickness, according to QPC — and lower density, which translates into parts with higher stiffness-to-weight ratios. While the company's headliner product features glass content of 55 percent by weight, products for underbody shields, door inner panels and sandwich top layers use a glass content of 40 percent.

SymaLITE's first commercial application was the underbody shield for the BMW 5/6 series, comprising four components formed in less than 60 seconds in a single four-cavity mold and resulted in a 30 percent (4 kg/8.8 lb) weight savings. The center areas of the parts are 4-mm/0.16-inch thick, optimizing stiffness and noise reduction, while the perimeters are 1 mm/0.04-inch thick for attachment and seal strength. SymaLITE also forms the load floor/trunk separator for the 2005 Crossfire roadster by DaimlerChrysler. This large, complex one-piece structure is made using a 2,000 g/m2 sheet for the separator and an 1,800 g/m2 sheet for the floor. The 90-second process adds pressure-sensitive adhesive-coated carpet on one side and polyester scrim on the other via in-mold decoration. QPC says that the product is under evaluation for other automotive load floors as well as interior trim components, such as door panels, and OEMs are considering it for roof modules, hoods and trunk lids, where it would be used behind a Class A surface material, such as coil-coated aluminum or polypropylene film.

 

 

A fourth headliner panel, VolcaLite, is Azdel's GMT Lite product, made with polypropylene reinforced by long chopped basalt fiber. Basalt, an inert rock found worldwide, is the generic term for solidified volcanic lava. Basalt fibers, a comparatively new fiber reinforcement, are now marketed internationally by several recently formed companies, including Albarrie Canada Ltd. (Barrie, Ontario, Canada), Basaltex (Wevelgem, Belgium), Hengdian Group Shanghai Russia & Gold Basalt Fibre Co. (Shanghai, China), Kamenny Vek (Dubna, Russia) and Sudaglass Fiber Technology (Houston, Texas). Its main advantages are higher service temperatures, higher modulus and better chemical resistance compared to fiberglass. It is intended as a replacement for both glass and carbon fiber reinforcements in composites. VolcaLite has been targeted for use in headliners, where it is said to offer ultrathin profiles (down to 3 mm/0.12 inch, a 50 percent reduction, compared to conventional products. Currently, VolcaLite is being evaluated by multiple Tier 1 automotive suppliers.

In the past 18 months, ENSINGER/Penn Fibre (Bensalem, Pa.) has introduced a variety of short glass fiber-reinforced thermoplastic sheet materials for underhood and other applications, sold under three brand names.

Pennite 4512, a Nylon 6 (polyamide) with 12 percent glass fiber reinforcement, was developed for air dams, ducts and radiator shrouds. Parts made from the material can withstand 280°F (138°C) continuous in-service temperature. However, the company notes that polyamides are hygroscopic (susceptible to moisture absorption), and therefore must be pre-dried, using a desiccant or a recirculating-type oven prior to thermoforming to avoid surface blisters caused by outgassing.

Penn Fibre's two additional panel products are formed using thermoplastics developed by Ticona (Florence, Ky.). The first, a sheet material made form Ticona's Celcon acetal co-polymer resin and 15 percent glass fiber reinforcement, was developed for underhood and gasoline tank applications where the structural integrity and chemical resistance of the material meets end-use requirements. (Celcon and Pennite 4512 are both used in current production vehicles, however Tier 1 suppliers are protective of details, and thus, Penn Fibre is not able to discuss specifics.)

The second product is glass-fiber reinforced polyphenylene sulfide (PPS) sheeting, using Ticona's Fortron PPS. Sold as monolayer sheets and in rolls to 48 inches/122 cm wide and thicknesses between 0.010 inch and 0.25 inch (0.25 mm and 6.4 mm), the materials are available with optional backings that provide gluing surfaces in multilayer applications. The sheets are preheated to between 610°F and 625°F (321°C and 329°C) and can be formed using aluminum tools without a cooling system. The molds are preheated to 390°F/199°C and total cycle time from preheating sheet to forming and final cooling is between 60 and 90 seconds. The material's thermal performance, high strength, inherent flame retardant properties and chemical resistance makes it suitable for stationary and mobile chemical tanks, underhood automotive parts, and interior panels and other large, thin-walled elements in buses, aircraft and railcars, says the company.

Although each brand comes in standard sizes, most product is delivered to customer spec, in terms of thickness, width and length in order to provide optimum-sized blanks for thermoforming.

NATURAL FIBER PANELS

Natural fibers and wood flour are perhaps the oldest reinforcements used in plastics, dating back to Bakelite, the first plastic made from synthetic polymers (circa. 1909), in which they were used to reduce cost, control shrinkage and improve impact resistance. Although they were replaced with mineral fillers and fiberglass in the 1950s and 1960s, natural fibers are making a comeback. This trend started in Europe, where end-of-life recycling requirements have stimulated development of natural fiber composites that combine plant fibers, such as abaca, flax, hemp, kenaf, sisal or jute with polyethylene, polypropylene (PP) and other thermoplastics, offering properties comparable to glass-reinforced thermoplastics, but at 70 percent of the weight and at lower finished-product cost.

The U.S. is catching up. Most major suppliers now offer natural fiber-reinforced products and are working to develop applications (see CT February 2006, p. 32).

FlexForm Technologies (Elkhart, Ind.) has introduced FlexForm panels, featuring a variety of sheet composites made from plant fibers, such as kenaf, hemp, flax, jute or sisal, blended with thermoplastic matrix materials, such as polypropylene or polyester. According to Flexform VP of sales Harry Hickey, the first panel product was developed by request: "One of our automotive customers in the U.S. had seen this type of product in Europe and wanted to develop it here," he explains. "They wanted the environmental advantages, but also improved weight and strength while maintaining one-step processing and competitive part cost." According to Hickey, FlexForm products offer a lighter weight and more environmentally friendly alternative to wood flour-filled plastics, as well as a 25 percent improvement in strength in applications such as door panels and inserts, package trays, headliners, seat backs, sidewalls, pillars and center consoles. Flexform panels can be thermoformed at 392°F (200°C) and 55 psi (0.379 MPa). The materials are used in numerous production automobiles and are being marketed to RV and trailer manufacturers for sidewalls. Other markets include a variety of consumer goods, e.g., furniture, office partitions and ceiling tiles.

G.O.R. Applicazioni Speciali SpA (Buriasco, Italy), a subsidiary of Solvay Industrial Foils (Brussels, Belgium) has developed three classes of natural fiber-reinforced thermoplastics that can be extruded as thermoformable, recyclable flat sheets. The base product is Wood-Stock, a family of polypropylene (PP) composites with 5 to 55 percent wood flour loading by weight. It was developed to meet customer needs for an inexpensive, recyclable material for automotive interior applications, such as door panels, rear shelves and pillars. Gornaf, a new material, is comprised of polypropylene reinforced from 5 to 35 percent by weight with long sisal fibers (20 mm to 30 mm). The longer fibers reduce part weight and bring higher tensile and flexural strength to components with demanding requirements. G.O.R. has performed recycling tests on Gornaf door panels and confirmed that over 90 percent of the material (by weight) can be re-used. Therefore, G.O.R. buys manufacturing scrap from its customers, which then is reground and mixed with virgin materials for use in production of new panels. Tecnogor, the second generation of Gornaf, is reinforced from 10 to 40 percent by weight with even longer natural or glass fibers (40 mm to 250 mm). There are currently a total of 150 different variations among the three products, which have been developed to provide solutions for specific customer requirements.

G.O.R.'s technical marketing manger Ariano Odino says thermoforming of these products can be done with a relatively inexpensive infrared oven, a 200-ton hydraulic press and a steel mold with water-cooling system. "In the standard process we use, sheets are heated at 180°C to 190°C (356°F to 374°F) for 50 seconds and then transferred automatically to the mold where pressure of 8 to 10 kg/cm2 [114 to 142 psi] is applied for 40 seconds." he explains. "You can obtain a finished part with coverstock on both sides (fabric or vinyl) and integrated plastic brackets, all molded in one step, in a very fast cycle time."

 

 

Gornaf has been used in the front and rear door panels for the Peugeot 406 Coupe. Newer Tecnogor currently is being evaluated by potential customers.

SELF-REINFORCED COMPOSITES

Recyclability is a primary — but not the only — driver in the development of self-reinforced plastics (SRPs). The following three SRP sheet materials were developed initially for automotive applications, but also are proving useful in industrial, sporting goods and consumer goods applications. The resulting composite, basically a mono-material, offers no impediment to recyclability, and attains specific strength and stiffness properties comparable to fiberglass-reinforced composites. This is due to polypropylene's very low density, which, SRP manufacturers say, offers 40 to 60 percent weight savings versus glass mat thermoplastics (GMTs) and other traditional GRP materials. Additional benefits include the soft crash behavior imparted by the ductile failure mode of polypropylene, which is said to prevent splintering, and the product's impact resistance, which it maintains even at very low temperatures.

Curv is manufactured by Propex Fabrics (Gronau, Germany). Extruded polypropylene film is stretched into tapes with exceptionally high stiffness and strength. These tapes are then woven into fabrics and undergo a patented hot compaction process in which the surface of every tape is partially melted, creating a matrix which bonds the tapes into a self-reinforced composite.

Thermoforming is achieved using pressures of 5 bar (73 psi) and up, depending on the complexity of the part, and temperatures of 150°C to 160°C (302°F to 320°F). Typical cycle times are less than 60 seconds. The consolidated sheets are slit to standard or customer specified lengths to 3m/9.8 ft and widths to 1,360 mm/53.5 inches, in thicknesses from 0.3 mm to 3 mm (0.01 inch to 0.12 inch).

Automaker DaimlerChrysler has evaluated Curv for underbody shields, and several processors are testing it for use as a local reinforcement material for injection-compression and compression molded parts. The product also is being marketed for bumpers, body and underbody panels, interior headliners, door liners, load floors, pillar trim and rear parcel shelves. Other applications include building cladding, personal protective equipment, sporting goods, briefcases and luggage, audio speakers and even shoe inserts.

Milliken & Co. (Spartanburg, S.C.) produces Moldable Fabric Technology (MFT) sheet stock using PURE technology through a licensing agreement with PURE's manufacturer, Lankhorst-Indutech (Sneek, The Netherlands).

Lankhorst-Indutech uses a patented process to produce tape-like yarn using three flat coextruded polypropylene layers. The middle layer has been drawn out under tension and heat to orient the polymer chains along the tape's 0° axis to optimize high strength and high modulus. This layer is sandwiched between two thin outer layers specially formulated with a lower melting point. The tape-yarns can be woven into fabrics. According to Lanhorst-Indutech's Astrid Wijninga, "PURE's specific impact performance is so good that it is now being considered for use in protective applications in sporting goods and anti-ballistic applications in the defense industry." (Commercialization is expected, respectively, in summer and fall of this year.) Additional targets include liners for truck trailers, kayaks, canoes, body panels for personal watercraft and snowmobiles, car-top carriers, recreational vehicles, piping and construction.

Milliken uses PURE fabrics to create its MFT sheet stock. The sheet is comprised of multiple layers of twill or plain-weave fabric woven from PURE yarn. During processing, the company's hot compaction process applies heat at a temperature above the melt point of the yarn skins, but below that of the middle layer. This permits consolidation of the fabric layers, as the low-melt-point outer layers of the yarn melt and impregnate the woven fabrics, but maintains the integrity of the oriented polymer chains in the middle layer — a key to optimizing properties such as impact resistance.

MFT parts are thermoformed at relatively low pressures, starting at 3 bar (44 psi) and temperatures from 150°C to 160°C (302°F to 320°F). Typical cycle times are less than 1 minute and can be as low as 25 seconds, depending on the complexity of the part. Finished sheets can be supplied in 0.3 mm to 3 mm (0.01 inch to 0.12 inch) in thickness (greater thicknesses are available on request) and are cut to customer-specified width and length and shipped on spools.

Preconsolidated sheet stock for load-bearing applications features continuous fiber - not only glass, but carbon and aramid as well.

In the world of reinforced thermoplastics, thermoformable composite panels for load-bearing applications are a relatively recent but fast-growing development. In structural and semi-structural composites applications, they were preceded by thermoplastic prepregs, which were developed to replace thermoset prepregs in niche aerospace applications. The resulting unidirectional tapes and semipregs featured continuous glass, aramid or carbon fiber reinforcements combined, early on, with engineering thermoplastics, such as polyethersulphone (PES) and polyetherimide (PEI) matrices and, more recently, with higher performing polyphenylene sulphide (PPS) and polyetherketoneketone (PEKK). But the expense of hand layup and the capital cost of machinery for automated manufacture (such as filament winding or automated tape laying equipment) have deterred growth. Thermoformable panels are helping suppliers overcome these barriers to product development and spur growth rates in the use of fiber-reinforced thermoplastics at a rate of 20 percent per year.

Unlike preconsolidated panels profiled in Part I (see CT April 2006, p. 36), structural-grade panels more closely resemble load-bearing thermoset advanced composites by employing continuous fiber reinforcement. Yet they represent a significant step forward compared to previous thermoset and thermoplastic technologies in that they shift responsibility for the fiber/resin ratio and fiber orientation or architecture to the panel manufacturer, freeing the part fabricator to focus on a smaller set of forming variables. This not only simplifies the fabricator's job but - because the panels can be mass-produced on automated production lines - increases the consistency and repeatability of finished reinforced thermoplastic components as well. Moreover, the fabricator's cycles are shorter, and finished products have greater toughness and impact resistance than thermoset composites and offer recyclability as well.

In the late 1980s, continuous fiber-reinforced thermoplastic sheet material was first used to form aircraft flooring for several European aircraft. More recently, structural parts made from thermoformed glass-reinforced PPS panels have been put to notable use on the wing leading edges of both the A340 and new A380 commercial airliners built by Toulouse, France-based Airbus Industrie (see "Thermoplastic Composites Gain Leading Edge on the A380," in CT's sister magazine, High-Performance Composites, March 2006, p. 50). These successes helped stimulate production of a number of similar products.

Structural Glass

Predominantly supplied as a unidirectional prepreg, Plytron, a polypropylene (PP) composite manufactured by Gurit (Flurlingen, Switzerland), also is sold in sheets formed from multiple layers of continuous glass/PP, with custom-tailored layup and fiber orientation. Currently, Glasseiden GmbH (Oschatz, Germany) supplies the fiberglass and Borealis A/S (Linz, Austria) provides the PP polymer. Both fibers and matrix were specifically developed for Plytron. Gurit is continuing Plytron optimization and development, with the help of these and other suppliers.

Typical layups are either 0°/90° or quasi-isotropic, but numerous stacking sequences are possible. Plytron sheets are consolidated and have a fiber content of 60 percent by weight.

Gurit markets Plytron as an alternative to commingled yarn products that combine glass and polypropylene fibers. Christophe Bourban, key account manager for Gurit Suprem, explains that Plytron preconsolidated sheet offers shorter cycle times than composites molded conventionally from raw fiber and resin - cycle times from 2 minutes to as little as 45 seconds can be achieved when stock is preheated between hot platens and then formed on a room-temp mold. Generally, thermoforming equipment heats parts to 185°C/365°F and applies 40 bar/4 Mpa pressure.

The one limitation may be with regard to part geometry. "If the part contains a deep draw or sharp curvatures, then slits in the material may be needed locally to ensure proper drapability," says Bourban. "However, parts have been produced with surprisingly good drapability at the cost of slightly longer cycle times."

Springs for high-quality Swiss bed manufacturer Bico are made using Plytron unidirectional plates, which are thermoformed and stamped. More than 5 million parts have been produced to date, with benefits including light weight, a virtually endless service life, and a competitive price. Plytron also has demonstrated its ability to offer Class A surface finish without additional and expensive surface treatment in automotive applications. BI Composites (Bridgtown, Cannock, U.K.) and MG Rover (U.K.) developed an automotive car hood, using a sandwich construction of PP nonwoven mat core and Plytron skins. "Advantages are the modest tooling costs, which allow for competitive pricing for small series of sport-version cars," says Bourban, adding that, in tests, "the use of PP near the heat radiated by the engine proved to be no problem, even for long-term service. This is possible due to the continuous glass fiber reinforcement. Unfortunately, MG Rover went bankrupt in 2005, so the bonnet did not become a commercial product."

To meet growing demand, Plytron production has been increased by a factor of five from 2004 to 2005 and further increases are planned for this year. The product is targeted for automotive components, such as floor panels, bumper beams and hoods, home appliances and pipe reinforcement as well as as local reinforcement in combination with GMT/LFT for high-volume applications. The product is currently available at a maximum width of 600 mm with an individual ply thickness of 0.27 mm. The sheet product can be supplied from 1,000 mm lengths to 440-meter rolls packaged on palettes. Future developments will include carbon fiber reinforcement and wider range of thermoplastics including polyamide nylon 6 (PA6), thermoplastic polyurethane (TPU), polyphenylene sulfide (PPS) and blends.

TWINTEX P PP is a consolidated plate made from TWINTEX commingled polypropylene (PP) and continuous glass fibers. TWINTEX commingled fiber was introduced in 1997 and is made by Saint-Gobain Vetrotex (Chambéry, France). The glass content is 60 percent by weight, and fiber reinforcement is either a balanced twill or plain-weave (4/1) fabric. Products include areal weights of 745, 935, 1,485, 1,870 and 2,970 g/m2. The recyclable material reportedly has excellent mechanical properties and its PP matrix lends it greater ductility and better dimensional stability in a wet environment than standard thermosets and other thermoplastics.

TWINTEX P PP is sold in standard widths of 104 cm or 152 cm (40.9 inches or 59.8 inches) and comes in rolls or cut-to-size plates. After preheating above the melt point of PP (180°C to 230°C/360°F to 450°F), TWINTEX thermoforms at various pressures, depending upon the exact forming process used: diaphragm - 1 bar to 8 bar (15 psi to 116 psi); thermo compression - 25 bar to 200 bar (363 psi to 2900 psi); sandwich thermo compression -1 bar to 5 bar (15 psi to 73 psi); or comolding with GMT or LFT as local reinforcement - 25 bar to 200 bar. TWINTEX also is now available with a thermoplastic polyester (PET) matrix.

TWINTEX reportedly has shown promise for thermoformable sandwich structures, featuring TWINTEX skins and either foam or PP honeycomb core. Produced as flat cored panels, they can be formed into shaped parts by low-pressure stamping. Textile coverings or carpets can be easily comolded during stamping for automotive interiors. Applications include the 4.2 kg/9.3 lb trunk floor developed by automotive systems manufacturer Peguform (Saint Marcel, France) for the Nissan (U.K.) Primera Estate. TWINTEX 935 g/m2 skins and polypropylene honeycomb core yield the specified stiffness-to-weight ratio. Peguform produces 100 parts per day using its patented Sandwiform molding process, in which carpet is comolded with the composite in a single step. Additionally, Jacob Composites (Wilhemsdorf, Germany) developed and manufactured 1,500 seat back structures for the BMW M3 CSL, using a sandwich of TWINTEX skins and polyether sulfone (PES) foam, with polyester carpet over-molded on one side in a one-step thermoforming process. The 5 kg/11 lb part offered more than a 50 percent weight reduction versus steel, as well as good acoustic insulation, excellent crash performance and low capital investment, due to the low-pressure molding process.

Plytron and TWINTEX also are marketed, in part, as effective local reinforcements for GMT and LFT compounds. For example, TWINTEX, a non-flowing material, can be selectively placed in specific local areas, in combination with either GMT or LFT, which are flowable materials, enabling the two systems to work together. The end-result is a part with integrated ribs, which have the necessary high section modulus, all in one-step molding.

Advanced Composites

Developed initially for aerospace applications, the following two products were developed as a more cost-effective alternative to the labor-intensive hand layup of thermoset prepregs. "A limiting factor of thermoset composites is the costly and complex autoclave process," explains Willem van Dreumel, director of research and development at Ten Cate (Nijverdal, The Netherlands). "Many smaller components like ribs, brackets and curved panels, are very suitable for thermoforming technologies, which offer a typical four-minute cycle time at a very low cost compared to autoclaved products."

Ten Cate developed the basic technology for Cetex continuous fiber-reinforced thermoplastic laminates in the 1980s, in cooperation with Delft University (Delft, The Netherlands). Standard Cetex products feature PEI or PPS matrices with glass, carbon or aramid fabric reinforcement. Glass is supplied by PPG Industries (Pittsburgh, Pa.) in the U.S., while the carbon fiber is sourced from Toray-Soficar (Abidos, France). PEI is supplied in granulate form by GE Plastics (Pittsfield, Mass.) and PPS is supplied as film by Amcor (Ghent, Belgium) and as granulate by Ticona (Kelsterbach, Germany). Sheets are typically 3.8m by 1.3m (12.5 ft by 4.3 ft) and range in thickness from 0.2 mm to 50.0 mm.

Thermoforming guidelines for carbon fiber/PPS Cetex sheets recommend preheating at temperatures between 300°C and 330°C (572°F and 626°F), with tool temperatures of approximately 180°C/356°F, at a forming pressure of 40 bar/580 psi.

According to van Dreumel, there are roughly 1,500 different part numbers in Cetex PEI or PPS composite on Airbus aircraft. This number is expected to grow significantly with many thermoplastic composite parts on the new Boeing 787 and the development of the Airbus A350.

Ten Cate also supplies the material for the A380 engine air intakes made by Airbus France. "The air intake is an innovative no-splice design made possible by the use of thermoplastics. The acoustic liner is manufactured as a single barrel, vesus the traditional two to three panels, which removes the acoustic disturbance caused by the spliced joints, giving the A380 a very low noise profile," says van Dreumel.

TEPEX dynalite, developed by Bond-Laminates (Brilon, Germany), is available as semi-preg or preconsolidated sheet. The sheet stock is available in a wide variety of combinations of glass, carbon and/or aramid fibers and PP, TPU, PPS, and polyamide (PA 6/Nylon 6), PA 12, PA 4,6 and PA 6,6 matrices. Sheets are consolidated in a double-belt laminating press, resulting in products with less than 2 percent void content and fiber volumes ranging anywhere between 35 and 55 percent, in thicknesses as thin as 50 mm to as thick as 6.0 mm, and may include up to 20 layers. "The dynalite materials offer customized layup, varying reinforcement type, thickness and fiber volume to satisfy the cost and performance requirements of a specific application," says Bond-Laminates' managing director Joost van Lindert. "It is our philosophy to solve many application development issues by optimizing the material rather than leaving the developers to maneuver around engineering compromises with the standard materials."

Bond-Laminates also produces a TEPEX flowcore product, which consists of long fibers (30 mm to 50 mm or 1.18 inches to 1.97 inches), similar to traditional GMT materials, with the difference that they are based on engineering resins. For example, TEPEX flowcore 102-RGR/PA6 is a commercial-grade product with random glass reinforcement (RGR) and PA 6 matrix.

"These materials are often combined with dynalite to enable the molding of stiffeners and ribs along a continuous fiber-reinforced structure," says van Lindert. The TEPEX dynalite material (fabric-reinforced) and the TEPEX flowcore material (random-fiber reinforced) both come in sheet form, are heated and placed in the mold together. The material size is slightly smaller than the final part size. The flowcore material flows to the edges of mold cavities and fills the rib and stiffener shapes in the mold. "It is very cost-effective, as it eliminates the cutting procedure after molding a part, which also reduces the cutting waste to virtually zero." TEPEX flowcore materials are intended for automotive and industrial structures for which technical requirements cannot be met by glass/PP, GMT or injection molded thermoplastics.

"Most TEPEX materials have cycle times of 30 to 60 seconds, depending on the level of automation the customer has installed," says van Lindert. "The main variable is the cooling time of the thermoplastic matrix in the tooling." TEPEX dynalite fiberglass-reinforced and carbon fiber-reinforced polyamide 6,6 composite laminates require forming temperatures between 280°C and 300°C (536°F and 572°F), and consolidation pressures of 5 to 100 bar (73 psi to 1,450 psi). He notes that molding temperatures for PP- and TPU-based products range from 190°C to 300°C (374°F to 572°F). TEPEX can be supplied in a maximum width of 1,350 mm/53.2 inches in lengths limited only by transportation requirements, or in customer-specified sheet sizes.

The dynalite glass/PP and glass/PA6 are used mainly in automotive applications replacing aluminum for cost and weight savings. Glass/TPU and carbon fiber/TPU are primarily used in orthopedic and sporting goods applications, offering superior performance, compared to unreinforced plastics. Carbon fiber/PA 66 dynalite was developed for structural sporting goods and helmet shell applications, and PPS materials are being used in aircraft interiors at lower cost than traditional thermoset composites. Dutch Thermoplastic Composites (Lelystad, The Netherlands) is thermoforming 0.2-mm to 5.0-mm-thick (0.01-inch to 0.20-inch) sheets of Tepex carbon fiber/PPS to replace aluminum in lumbar and thigh supports, armrest table covers and shields for video screens. The Tepex lumbar support weighs around 150g/5.3 oz, saving 130g/4.6 oz versus the aluminum part at 280g (9.9 oz). This cuts roughly 72 kg/158 lb per aircraft in a 555-seat configuration on the Airbus A380. Other applications include an advanced composite sandwich material applied in the new generation of Bowers & Wilkins loudspeakers and a high performance ski boot developed by Rossignol-Lange, using overmolded TEPEX dynalite/TPU (see photo p. 32).

New to the market is Porcher Industries' (Badiniéres, France) line of preconsolidated thermoformable and weldable sheet stock. The sheet stock is made from its PiPreg reinforced thermoplastic prepreg material, available in either unidirecitonal or woven E- and S2-glass, carbon, or aramid fibers impregnated with any one of a number of high-performance thermoplastic resins, including PEEK, PPS, PEI, TPU and polyamide 12. Reinforcement, resin, fiber orientation and fiber/resin ratio can be tailored to the end use. Benefits include increased composite parts manufacturing speed and the possibility of making prototypes and pre-series in low quantities.

Cored & Core-like Panels

Using a single-step manufacturing technology, FITS Technology (Driebergen, The Netherlands) produces lightweight, high-strength, high-stiffness FITS (Foamed In-situ Thermoformable Sandwich) panels, featuring an isotropic PEI foam core bonded to continuous fiber-reinforced PEI faceskins. FITS was initially developed in a Delft University research program. "The goal was to make a product having an airy core with solid surfaces, similar to the excellent structural design of bones," notes FITS managing director Martin de Groot.

One of the initial targets for FITS is replacement of traditional aramid honeycomb cored sandwich panels in overhead storage bins on commerical aircraft. Roughly 25 percent of aramid-cored panel weight comes from potting compound, paint, inserts, and decorative surface film. For FITS panels, this drops to only 5 percent. "FITS cannot compete with aramid on its own because the honeycomb core is so lightweight," says de Groot. "However, FITS can compete if you take advantage of its its potential to eliminate ... potting of fastener holes and waiting for potting compound to cure before installing fasteners." In FITS panels, thermoplastic fastener inserts can be installed via ultrasonic welding, offering dramatic time and cost savings. "So with FITS, you start with a higher weight panel, but end up with a lower weight finished part at a much lower cost for high-volume applications," de Groot maintains.

Source: FITS TechnologyFITS Technology

FITS panel thus meets all end-use part requirements and offers a 5 to 50 percent weight savings at a very significant reduction in final part cost, says the company. If the weight and cost reduction demonstrated for overhead storage compartments were extended to other interior components - cargo ceilings and floors, cabin floors and components for galleys and trolley carts - the total savings per aircraft could be significant, says de Groot. Reportedly, FITS panels meet all flammability and smoke toxicity requirements for aircraft interiors and have greater damage tolerance and peel strength than honeycomb-cored sandwich panels.

Typical thermoforming temperatures for FITS are 330°C to 350°C (626°F to 662°F), which is a little lower than the glass transition temperature of the PEI facings. Forming pressure is around 0.321 Mpa/47 psi, depending on the density of the in-situ PEI foam. A heated die or tool is used for shaping followed by a consolidation die or tool, which is kept at a temperature below the melt temperature of the thermoplastic faceskins. The process can include in-mold decoration: Faceskins can be colored white or receive a transferred decoration - using a printed paper technique.

A wide variety of faceskins are available in addition to PEI, including PES and polyphenylene sulfone (PPSU). Facings are reinforced with style 7781 fiberglass fabric impregnated to a fiber content of 32 percent by volume, but may also use aramid and carbon fibers. Top and bottom faceskins are typically 0.7 mm/0.7 inch thick and faceskin layups per panel can be 1 ply top/1 ply bottom, 1 ply top/2 plies bottom and 2/2. FITS panels are manufactured with a thickness of 5 mm to 25 mm (0.2 inch to 1 inch) and a density of 85 kg/m3 to 150 kg/m3 (5.3 lb/ft3 to 9.4 lb/ft3).

Source: Bond-LaminatesTepex preconsoliated RTP materials, developed and manufactured by Bond-Laminates (Brilon, Germany), are available in a variety of colors and patterns.

Rail-Lite thermoformable long glass fiber-reinforced thermoplastic (LFRT) sheet is supplied by Azdel Inc. (Southfield, Mich.), a joint venture of GE Advanced Materials (Pittsfield, Mass.) and PPG Industries. Rail-Lite is made from GE's Ultem PEI resin. During processing, the glass-reinforced PEI resin expands, lending the matrix a foam-like character that provides desirable sound absorption and heat-insulation properties. Additionally, about half its volume is air, making the material very lightweight - about half the specific gravity of aluminum and fiberglass panels of similar or equivalent strngth and stiffness. Additionally, PEI is inherently fire retardant, enabling it to char when exposed to flame, emitting very low levels of smoke.

Unidirectional Plates

Rail-Lite forms the structural component of HushLiner FR acoustic panels produced by Azdel partner and acoustic/thermal insulation specialist American Acoustical Products (Holliston, Mass.). The proprietary five-layer sandwich panels are designed for use as contoured acoustic ceiling panels. The panel's top layer is a perforated solvent-, stain- and graffiti-resistant Indura GT decorative laminate film, developed by Schneller Inc. (Kent, Ohio) for contoured railcar interior surfaces. Metro-North Railroad, the third-largest commuter railroad in North America, is using HushLiner FR as a replacement for traditional acoustic ceiling panels in its passenger railcars. The panels comply with the ASTM flame and smoke standards mandated by the U.S. Federal Railroad Assn. (U.S. FRA 49 Code of Federal Regulations [CFR] Part 238) for train passenger cars and locomotive cabs, as well as Germany's DIN5510, Part 2 S4/SR2/ST2 rating. Azdel is marketing Rail-Lite into rail interior components such as window masks, ceiling panels, seat backs, arm rests, tray tables, stowage bins, valances, and partitions. GE Advanced Materials also has formed a joint development agreement with the largest OEM supplier of train interiors in China, which plans to use multiple grades of Rail-Lite in its passenger train interiors.

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