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Narrow UD tapes to bridge the ATL-AFP gap
It is well understood that automated tape laying (ATL) and automated fiber placement (AFP) were the enabling technologies in the application of carbon fiber composites in major aerostructures for the Boeing 787 and the Airbus A350 aircraft. Prior to the development of these planes, composites had been applied in gradually increasing amounts in commercial aircraft for more than 30 years, but mainly in secondary structures using hand layup and some automated manufacturing processes.
With the 787 and the A350, however, Boeing (Seattle, Wash., U.S.) and Airbus (Toulouse, France) responded to demand for lighter weight aircraft, which accelerated adoption of composite materials and processes for use in fuselage skins, stringers, frames, wing skins, wing spars, wing boxes and tail structures. ATL and AFP led the charge, allowing each OEM, and their suppliers, to efficiently lay down large amounts of prepregged UD-tape and tows.
ATL found a place fabricating wing structures, which, being modestly contoured, took advantage of the wide format (3, 6 or 12 inches) of the tape products, which could be laid down quickly. However, what ATL offered in speed and volume it sacrificed in conformability.
AFP, on the other hand, which lays down multiple tows 0.125 to 0.5 inch wide, found a place fabricating fuselage and other more contoured structures that demand maximum flexibility and conformability. However, what ATL offered in conformability it sacrificed in speed and volume.
Further, as enabling as these technologies were, they clearly reflected the state of ATL/AFP art at the time of the planes’ initial development, almost 20 years ago now. Indeed, the production pace of the 787 and the A350 (each now less than 10/month in light of the coronavirus pandemic) is well-aligned with previous-generation ATL/AFP technologies, which are relatively slow. These technologies also depend on human operators to provide in-process visual inspection and quality control, checking for the laps, gaps, wrinkles, foreign object debris (FOD) and other flaws endemic to the automated laydown process. This quality control step represents a significant bottleneck in the manufacture of composite structures.
But as commercial aircraft manufacturers look to the future (well beyond the coronavirus pandemic) and the aircraft they will develop — particularly new single-aisle (NSA) programs to replace the Boeing 737 and Airbus A320 — shipset volumes are likely to be on the order of 60-100 per month. This demands composite materials and process capability orders of a magnitude more efficient than those used to fabricate structures for the 787 and the A350.
Honeycomb panel applications
EconCore has granted plastic film company Renolit a license for the continuous production of honeycomb panel.
Renolit has reportedly used the honeycomb in its Gorcell range of products for automotive, outdoor kitchens, truck superstructures, and bakery panels applications. More recently, Renolit has produced products for gardens, balconies and terraces made with honeycomb panels.
According to EconCore, the honeycomb has helped Renolit improve panel planarity, reduce golf ball effect, and create smooth, scratch free surfaces.
The Renolit Gorcell production process includes film unwinding, vacuum forming, core calibration, skin layer lamination, panel calibration and cutting.
This story uses material from EconCore, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier.
Scanning electron microscopy and digital image correlation observations reveal the failure mechanisms of overmolded hybrid composites. The failure behavior of overmolded hybrid composites is mainly CFRT laminates failure for all cases. The evolution of non-uniform strain fields indicates that the fracture of overmolded thermoplastic composites may initiate at the edges and spread out to the far fields.
Wood is a renewable, ecological raw material employed to manufacture high quality furniture and everyday products. Its versatile utilization in numerous branches of the wood industry exerts considerable influence on the intensive exploitation of wood resources. The above-mentioned factors clearly show that there are reasons to replace traditional panel materials, such as plywood (PW), particleboard (PB), oriented strand board (OSB), medium-density fiberboard (MDF), and high-density fiberboard (HDF), with lightweight sandwich honeycomb panels. These panels are characterized by relatively high strength and stiffness (Khan 2006; Schwingshackl et al. 2006; Jen and Chang 2008; Smardzewski 2013). According to Negro et al.(2011), the density of light honeycomb panels should not exceed 500 kg/m3.
The use of honeycomb panels with paper cores manufactured from hexagonal cells is quite widespread. However, during the manufacturing process these cells acquire irregular shapes of non-regular hexagons (Xu et al. 2008). In a study conducted by Smardzewski and Prekrat (2012) it was demonstrated that the core of a honeycomb panel made of irregular hexagonal cells placed between two HDF panels equalizes quite well the stresses that develop in the facings. The above researchers observed that the stiffness and strength of the honeycomb panels were affected significantly by the paper grammage as well as the cell shapes and dimensions.
Honeycomb structures find widespread application in the motor, airplane, and military industries (Schmueser and Wickliffe 1987). In the furniture industry, due to economic reasons, honeycomb panels with thicknesses exceeding 25 mm (Barboutis and Vassiliou 2005; Smardzewski 2015; Smardzewski and Jasińska 2016) are preferred. Furthermore, physico-chemical properties of honeycomb panels with hexagonal cells manufactured from light metals are commonly known (Paik et al. 1999; Schwingshackl et al. 2006; Said and Tan 2008).
To increase the stiffness of wood-based honeycomb panels, the type and thickness of their facings (Meraghni et al. 1999; Sam-Brew et al. 2011; Chen and Yan 2012) were changed, the paper used to manufacture them was impregnated, and the dimensions as well as the shapes of the core cells were changed (Majewski and Smardzewski 2012). In addition, recommendations were made regarding factors that should be taken into account during the production process of paper cores of honeycomb panels intended for the furniture industry (Sam-Brew et al. 2011). For the core with hexagonal cells, these suggestions included: cell dimension, filling height, filling density, as well as cell orientation with respect to the panel sheet. In addition, it was confirmed many times that the honeycomb panel stiffness depends on the stiffness of the external facings. On the basis of a four-point bending, it was demonstrated that to reduce deflection of a honeycomb panel with a paper core and wood base facings, core cells should be as small as possible, whereas the core height should be as large as possible (Sam-Brew et al. 2011). It has been shown that honeycomb panels have higher values of shear modulus and higher stiffness when planes of common core cell walls are oriented parallel to the longer side of the panel (Bitzer 1997). The enlargement of the inclination angle of the cell walls increases the panel density and, by doing so, it significantly enhances its strength and stiffness (Majewski and Smardzewski 2013).
Hexagonal, regular core cells ensure panel isotropy, whereas the elongated cells affect their orthotropy (C?té et al. 2004; Smardzewski and Prekrat 2012). The honeycomb panel core and facing isotropy exert a positive influence on the processes of their cutting by minimizing the amount of waste during the production process. Simultaneously, isotropy assures the uniform bending stiffness in mutually perpendicular directions. In contrast, orthotropy interferes with panel cutting efficiency, although it does has an advantageous influence on improved stiffness and strength of rectangular panels along one preferred direction. This is an exceptionally useful property when designing shelves and horizontal partitions in cabinet furniture. Rectangular cells constitute a special case of core polygonal cells. Their shape and arrangement in the honeycomb panel core can have a crucial impact on improved multilayer panel stiffness. Based on the available literature, it has not yet been analyzed to what extent elongated, rectangular paper core cells affect the mechanical properties of furniture honeycomb panels and the orthotropic strength of such panels.
The aim of this study was to determine the effect of the orientation of the rectangular cells of the paper core on the mechanical properties of three-layer furniture panels. The cognitive objective of the experiments was also to ascertain relative density and elasticity constants of the designed cells. The authors decided to compare the results of the empirical experiments of cell elasticity moduli with the results of analytical calculations. The practical goal of the investigation was to show the possibilities of substituting cores with hexagonal cells used in furniture panels with cores with rectangular cells.
Global Unidirectional Tape (UD Tape) Industry Research and Trend Analysis Report
In addition to lightweight, UD tape also has the advantages of thermoforming and other advantages, and can be used as a structural supplementary material. Automobile exhaust emissions are one of the main culprits of greenhouse gas sources, which also increase the environment and manufacturers’ costs. By using new materials such as UD tape, the vehicle can be made lighter and carbon emissions can be reduced. However, these fiber tapes are expensive and difficult to mass produce. To solve this problem, five European partners funded by the European Union gathered together to carry out a project called FORTAPE, covering the entire industrial chain. The project requires a wide range of beneficiaries to develop new integrated technologies that make the most effective use of materials and energy, so that UD tape can be better applied to vehicles and aircraft.
UD tapes using PP are easy to thermoform and can also be formed into complex shapes. In an EU initiative, it was first proposed to use a cost-effective method to produce unidirectional fiber belts, which can be used to manufacture and reinforce parts on cars and airplanes. This solution will make parts lighter and more environmentally friendly. UD tape can be used to enhance the mechanical properties of plastic parts, and can also be used to manufacture structural parts, strengthen and thermoform multilayers.
UD tape production focuses on three main axes: UD tape manufacturing, parts manufacturing, and process and part modeling. At present, three different fiber impregnation technologies have been studied internationally to develop innovative processes for manufacturing UD carbon fiber and glass fiber tape to increase fiber content. The use of UD tape as a window regulator to enhance automation will help meet the cycle and output requirements of the automotive industry. At the same time, a window frame manufacturing process using fire-resistant polyamide UD tape will be developed for the aviation industry.
The initial development focus has been primarily on automotive interiors, including seating area components, door side-impact beams, cross-car beams, brake pedals, steering-column holders, airbag modules, and front ends. “At this time of increasing fuel requirements for automotive, OEMs are putting a lot of emphasis on lightweighting,” says Calvin Nichols, market development manager for automotive seating at BASF in Wyandotte, Mich. BASF refers to the technology as “continuous fiber-reinforced thermoplastic” or CFRT, while Pittsburgh-based Lanxess typically calls it “nylon composite sheet hybrid technology.” Similarly, Engel in York, Pa., refers to its process as Organomelt and KraussMaffei, Florence, Ky., calls its version FiberForm. The technology has also been described as “organic sheet overmolding.”
Whatever the label, this technology also has significant potential for use in other markets. There are variants of the technology in development that will further the use of thermoplastic composites in a range of industries that are seeking lightweight but high-strength material options, as well as the low cost, automation, and short cycle times possible with injection molding.
Both Engel and KraussMaffei first demonstrated the technology in two elaborate molding cells at the K2010 show in Dusseldorf, Germany. There, Engel molded a steering-column holder and KraussMaffei a door side-impact beam. Both used Tepex composite sheets from Germany’s Bond-Laminates GmbH and nylon overmolding compounds from Lanxess. (Lanxess recently acquired Bond-Laminates.) The two demonstrations used robots (linear or six-axis) to preheat the sheet in an oven at 300 C for 30-40 sec and then transfer the hot sheet to the injection mold. Closing the mold preformed the sheet, and then more nylon was injected over it in specific areas. Cycle times ranged from 33 to 55 sec. (the latter limited by oven-heating capacity).
Engel’s part, with its more complex geometry, was laser-trimmed outside the mold. In the case of KraussMaffei, which compounded the long-glass overmolding compound direct from roving on its IMC injection molding compounder, the robot transferred the net-shaped part to a quality-check station after molding.
The two material suppliers displayed applications for the technology at K2010. Lanxess showed an Audi A8 front-end reinforcement molded by Germany’s Magna Decoma Exterior Systems, containing both aluminum and Tepex inserts overmolded with nylon 6. BASF displayed a seat back from Faurecia of France consisting of woven-glass/nylon sheet from California-based Performance Materials Corp., overmolded with a specially developed 35%-glass nylon 6 compound (BASF’s Ultramid CompoSIT XA3232) that combines stiffness, ductility, and Class-A-type finish. The part weighs about 20% less than standard seat backs and is expected to be commercial within the next two years.
WHERE IS IT HEADING?
Sources at these four suppliers foresee dramatic growth potential, starting with auto interior components but extending to exterior, chassis, and power-train applications. They also envision applications in aeronautics, trains, trucks, agricultural equipment, machinery manufacturing, and renewable-energy systems.
BASF’s Nichols says, “Glass in a unidirectional form is much stronger than other forms of glass or ferrous and nonferrous metals. Such a sheet composite overmolded with nylon 6 has tensile strength as much as five times that of metals. Strength-to-weight ratio is dramatically improved over metals—twice that of steel and three-to-four times higher than a standard injection molded glass-filled thermoplastic. Stiffness-to-weight ratio with the continuous-glass composite laminate overmolded with nylon is eight times as much as steel.”
Other thermoplastics considered as candidates for this technology include PP, PBT, PES, PEEK, nylon 612, and possibly nylon 66, depending in large part on how well they meet strict flammability requirements.
Meanwhile, the machinery suppliers both have recently introduced new equipment to further progress in this nascent technology. Engel is recommending its new v-duo vertical large tonnage machines for Organomelt systems. Hydraulically powered with energy-saving servo-driven pumps, they are offered in five sizes from 400 to 2300 metric tons. The larger sizes are aimed at continuous-fiber composites, with their easy mold access to facilitate loading of reinforcing fabrics and organic sheets and tapes.