Composite Manufacturing Technology (Soviet Advanced Composites Technology Series)
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The project was part of the ten-year research and development investment known as the composite affordability initiative, led by the AFRL. More than sensors and accelerometers were employed in the test aircraft to measure structural stresses in order to evaluate the technological reliability. After the aircraft climbed to an altitude of approximately 10,ft, the two-pilot crew conducted a series of airspeed, stability and control tests throughout the aircraft to see how the ACCA performed at varying speeds, altitudes and attitudes. The demonstration lasted for about 87 minutes.
Although the demonstration was expected in late to early , during fabrication of the composite fuselage, insufficient bond of the skin on the lower fuselage required fabrication of a second fuselage, leading to a delay. The major design changes included replacement of the fuselage aft of the crew station and the vertical tail of the Dornier aircraft, and use of advanced composite materials.
The high-wing Dornier jet was chosen in order to complete the requisite tasks at lower costs. The fuselage is Featuring an enlarged cargo door and cargo ramp, the stronger and wider fuselage was designed to accommodate two military standard L pallets. The design excluded the use of traditional fasteners like rivets, making the composite structure inherently aerodynamic.
Advanced prototyping and composite technologies were used in the aircraft, and the design included super-lightweight and super-strong composite materials fabricated by out-of-autoclave curing. Using expensive autoclaves that use a combination of heat and high pressure, the large composite sections in the ACCA were formed, cured and bonded together in room-sized ovens, minimising the part count. The reduction in parts further reduces the design and manufacturing complexities. Integrally stiffened skin could be found in the vertical tail.
The fuselage of Dornier J is made of aluminium alloys. As many as , parts can be turned out on a set of forged steel dies, using sheet molding compound SMC , a composite sheet material made by sandwiching chopped fiberglass between two layers of thick resin paste. To form the sheet, the resin paste transfers from a metering device onto a moving film carrier. Chopped glass fibers drop onto the paste, and a second film carrier places another layer of resin on top of the glass.
Rollers compact the sheet to saturate the glass with resin and squeeze out entrapped air.
The resin paste initially is the consistency of molasses 20,, cps ; over the next three to five days, its viscosity increases and the sheet becomes leather-like about 25 million cps , ideal for handling. The mold is closed and clamped, and pressure is applied at As material viscosity drops, the SMC flows to fill the mold cavity.
After cure, the part is demolded manually or by integral ejector pins.
A typical low-profile less than 0. Fiberglass thermoset SMC cures in seconds and overall cycle time can be as low as 60 seconds. Other grades of SMC include low-density, flexible and pigmented formulations. Low-pressure SMC formulations that are now on the market offer open molders low-capital-investment entry into closed-mold processing with near-zero VOC emissions and the potential for very high-quality surface finish. Composites manufacturers in industrial markets are formulating their own resins and compounding SMC in-house to meet needs in specific applications that require UV, impact and moisture resistance and have surface-quality demands that drive the need for customized material development.
Injection molding is a fast, high-volume, low-pressure, closed process using, most commonly, filled thermoplastics, such as nylon with chopped glass fiber. In the past 20 years, however, automated injection molding of BMC has taken over some markets previously held by thermoplastic and metal casting manufacturers.
In the BMC injection molding process, a ram- or screw-type plunger forces a metered shot of material through a heated barrel and injects it at In the mold, the liquefied BMC flows easily along runner channels and into the closed mold. After cure and ejection, parts need only minimal finishing. Injection speeds are typically one to five seconds, and as many as 2, small parts can be produced per hour in some multiple-cavity molds.
Parts with thick cross-sections can be compression molded or transfer molded with BMC. Transfer molding is a closed-mold process wherein a measured charge of BMC is placed in a pot with runners that lead to the mold cavities. A plunger forces the material into the cavities, where the product cures under heat and pressure.
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- A Brief History of Composites in the U.S.;
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The one-shot process takes roughly 90 seconds, producing a geometrically detailed part with no secondary operations. The base layer of the organosheet preform was a PAimpregnated mat made from recycled carbon fiber RCF , also a means for lowering part cost and carbon footprint. Filament winding is a continuous fabrication method that can be highly automated and repeatable, with relatively low material costs.
Computer-controlled filament-winding machines are available, equipped with from 2 to 12 axes of motion. This is called wet winding. However, a variation uses towpreg, that is, continuous fiber pre-impregnated with resin. This eliminates the need for an onsite resin bath. In a slightly different process, fiber is wound without resin dry winding. The dry shape is then used as a preform in another molding process, such as RTM. Following oven or autoclave curing, the mandrel either remains in place to become part of the wound component or, typically, it is removed.
One-piece cylindrical or tapered mandrels, usually of simple shape, are pulled out of the part with mandrel extraction equipment.
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Some mandrels, particularly in more complex parts, are made of soluble material and may be dissolved and washed out of the part. Others are collapsible or built from several parts that allow its disassembly and removal in smaller pieces. Some composite part manufacturers develop their own resin formulations. In thermoplastics winding, all material is in prepreg form, so a resin bath is not needed. The prepreg is heated, layed down, compacted, consolidated and cooled in a single, continuous operation.
Thermoplastic prepregs eliminate autoclave curing cutting costs and size limitations and reduce raw material costs, and the resulting parts can be reprocessed to correct flaws. The highest-volume single application of filament winding is golf club shafts.cars.cleantechnica.com/casadas-con-el-imperio-historia.php
Description of the Resin Curing Process—Formulation and Optimization
Fishing rods, pipe, pressure vessels and other cylindrical parts comprise most of the remaining business. Pultrusion , like RTM, has been used for decades with glass fiber and polyester resins, but in the last 10 years the process also has found application in advanced composites applications.
In this relatively simple, low-cost, continuous process, the reinforcing fiber usually roving, tow or continuous mat is typically pulled through a heated resin bath and then formed into specific shapes as it passes through one or more forming guides or bushings. The material then moves through a heated die, where it takes its net shape and cures. Further downstream, after cooling, the resulting profile is cut to desired length.
Pultrusion yields smooth finished parts that typically do not require postprocessing. A wide range of continuous, consistent, solid and hollow profiles are pultruded, and the process can be custom-tailored to fit specific applications.
Tube rolling is a longstanding composites manufacturing process that can produce finite-length tubes and rods. It is particularly applicable to small-diameter cylindrical or tapered tubes in lengths as great as 6. Tubing diameters up to mm can be rolled efficiently. Typically, a tacky prepreg fabric or unidirectional tape is used, depending on the part. The material is precut in patterns that have been designed to achieve the requisite ply schedule and fiber architecture for the application.
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The pattern pieces are laid out on a flat surface and a mandrel is rolled over each one under applied pressure, which compacts and debulks the material. When rolling a tapered mandrel — e. To impart bending strength to the tube, therefore, the fibers must be continuously reoriented by repositioning the pattern pieces at regular intervals. Automated fiber placement AFP.
The fiber placement process automatically places multiple individual prepreg tows onto a mandrel at high speed, using a numerically controlled, articulating robotic placement head to dispense, clamp, cut and restart as many as 32 tows simultaneously. Minimum cut length the shortest tow length a machine can lay down is the essential ply-shape determinant. The fiber placement heads can be attached to a 5-axis gantry, retrofitted to a filament winder or delivered as a turnkey custom system. Machines are available with dual mandrel stations to increase productivity.
Advantages of fiber placement include processing speed, reduced material scrap and labor costs, parts consolidation and improved part-to-part uniformity. Often, the process is used to produce large thermoset parts with complex shapes. Automated tape laying ATL is an even speedier automated process in which prepreg tape, rather than single tows, is laid down continuously to form parts.
It is often used for parts with highly complex contours or angles. Tape layup is versatile, allowing breaks in the process and easy direction changes, and it can be adapted for both thermoset and thermoplastic materials. The head includes a spool or spools of tape, a winder, winder guides, a compaction shoe, a position sensor and a tape cutter or slitter. In either case, the head may be located on the end of a multiaxis articulating robot that moves around the tool or mandrel to which material is being applied, or the head may be located on a gantry suspended above the tool.
Alternatively, the tool or mandrel can be moved or rotated to provide the head access to different sections of the tool.