Hi Everyone,
Here is some information about polymers which i havew collected in thye last few days. Please plan to spend 30 mins if you are interested in this material. Happy reading.
What is a "Polymer"
The word Polymer comes from the Greek "poly" meaning many, and "meros", parts or units. A polymer is a group of many units. You combine many monomers (one unit) to create a polymer.
Polymer is often used as a synonym for "plastic", but many biological and inorganic molecules are also polymeric. All plastics are polymers, but not all polymers are plastics. Plastic actually refers to the way a material melts and flows.
Commercial polymers are formed through chemical reactions in large vessels under heat and pressure. Other ingredients are added to control how the polymer is formed and to produce the proper molecular length and desired properties. This chemical process is called "polymerization".
A homopolymer results from polymerizing only one kind of monomer. A copolymer results from using different monomers. Homopolymers have the same repeating unit while copolymers (which can be random, block, or graft) can vary have different numbers of repeating units. A terpolymer results from using three different monomers.
Cyclopss along with Foster Miller has developed a Polymer which is in
the class of Engineering/High performance polymer:
Engineering polymers have properties towards the high end of the spectrum. Strength and thermal resistance are the most significant. Their price may range from two to ten times as much as a
commodity polymer. They are used in: housings, brackets, load bearing members, machine enclosures, and applications requiring wear resistance, long life expectency, flame resistance, and the ability to endure cyclic stress loading. (e.g. PC, POM, PBT)
The properties of high performance polymers are at the highest end of the spectrum, generally with very high strength and thermal resistance. They tend to be very expensive, priced above most
engineering polymers. They are used in high temperature, high stress applications, in harsh environments, and low to medium volume production. (e.g. PEEK, PEI, LCP)
The polymer that Cyclopss/Foster Miller plan to commercialize is planned to be a replacement for PMR15 which shows good characteristics. Price will be in the range of $300-$400 per Kilogram of compound resin which can be hardened in to virtually any shape. At this point a lot of tests are being conducted and more information will be available to general public soon. Base being used to form resin is carbon-graphite which becomes almost 1/3 in weight after being cooked. The existing polymers in the industry emanate carcinogenic byproducts and gases at high temperatures. That is where the joint development comes in as this new material behaves much better in high temperatures and the material does not emanate carcinogenic substances. With the current information we
cannot deduce that this material can be used in other industries like
automobile,boats and other light weight construction till we know for
sure what the price is going to be and the Durability of the material.
Application of advanced composites to aerospace can be divided into four categories: (1) aircraft, (2) rotorcraft, (3) spacecraft/missiles, and (4) engines/nacelle. Within each category a furtherdivision is possible. For example, aircraft can be divided into combat aircraft, large transport, and small aircraft, and further divided into military and commercial applications. The design and
manufacturing technology is different for each of the above categories; the difference is largely
dependent upon the requirements set forth by each category. A brief description of the requirements and constraints of each category is delineated below to help explain the impact on the design and manufacturing technology:
Aircraft
Combat. This application requires high performance (weight, strength, stiffness are critical) and tolerance of severe environments. It involves moderate production rates and moderate durability. Many complex structures are required, resulting in high cost ($600 - $800 per pound of finished structure).
An automatic tape layup (ATL) machine is currently used formanufacturing large, somewhat flat structures, such as skins. An automatic cutting machine (ACM) is used to cut plies and fabrics for
hand layup. Most of the complex and small parts are made by labor intensive hand layup.
Large Military Transport and Bomber. This application involves moderate to high performance in moderate to severe environments. Moderate production rates are typical and moderate to long
durability is required. A mixture of large and small structures with both simple and complex shapes is fabricated for this application. The result is relatively high cost ($400 - $700 per pound of finished structure).
ATL is currently used for manufacturing large structures. ACM is used to cut plies and fabrics for hand layup. Most of the complex and small parts are made by labor- intensive hand layup.
Commercial Transport. This application involves moderate performance in moderate environments. Higher production rates are typical. Long-term durability is a requirement. The cost of certification is high. It entails the fabrication of a mixture of large and small structures with simple and moderately complex shapes. There is a high demand for low cost ($250 - $400 per pound of finished structure). Safety is a paramount consideration. Conservative approaches are
typical due to the financial risks involved.
ATL is currently used for large structures in this application. ACM is used to cut plies and fabrics. Some filament winding is used, as is braiding for ducts and pultrusion for simple and long
structures. The industry is still relying heavily on labor-intensive hand layup.
Small Transport and General Aviation. This is a relatively low performance application, in a less severe environment. Moderate to low production rates are typical. Short to medium durability is
required. Certification cost is lower relative to the large transport category. Except for the wings and fuselage, small, less complex structures are involved for all-composite aircraft. Low cost is a
must ($50 - $200 per pound of finished structure).
Mostly hand layup is used in current manufacturing practice. ATL and ACM are used for some applications. Filament winding is used for some structures. No fancy tooling or manufacturing techniques are employed.
Rotorcraft
Military. This is a high performance application. Weight, strength, stiffness, and durability are critical. Operating environments are severe. Production rates are low to moderate. Battle damage
tolerance is important. There is a high usage of composites (e.g., in rotor blades, tail blades, fuselages, and booms). Cost is relatively high ($500 - $700 per pound).
Hand layup is used for rotor and tail blade manufacturing. ATL and ACM are used for fuselage and boom. There are some filament winding applications.
Commercial and General Aviation. These aircraft require low to moderate performance, and usually operate in moderate environments. Production rates are low to moderate. In this industry, there is a high usage of composites for rotor blades, tail blades, bodies, and booms. Moderate cost ($200 - $350 per pound) is typical.
Hand layup is currently used for rotor and tail blade manufacturing. ATL and ACM are used for some body and boom structures. There are some filament winding applications.
Spacecraft and Missiles
This is a high to ultra-high performance area. Weight, strength and stiffness are extremely critical. There are numerous special and unique requirements. These vehicles operate in severe to
extremely severe environments. Very low production rates are typical for some spacecraft (e.g.,satellites) but high for some others (e.g., small missiles). There is essentially no durability requirement -- it is a "one shot" deal. Extremely high costs ($1,000 to over $10,000 per pound) are typical.
Current manufacturing techniques require the use of high precision hand layup with extremely complex tooling. Precision filament winding is used for circular shapes. Because of low production rates, labor-intensive hand layup is the main manufacturing technique.
Engine/Nacelle
There are uniquely high performance requirements for this application. These parts operate in severe environments. There is a high demand for durability. For fan blades, there is an acoustic environment issue, and net shape and complex contour are requirements. Relatively high
production rates are a feature. Engine blades are expensive, whereas nacelles are produced at moderate cost ($770/lb finished in an automated process for blades, and $350 - $450 per pound for nacelles).
Precision hand layup is required currently for blade manufacturing. Tow placement is also used for this application. A combination of filament winding and hand layup is used for nacelles. Honeycomb construction is used for acoustic sound absorption in nacelles. Precision co-curing techniques are used for cascades.
BRIEF HISTORY OF EVOLUTION IN COMPOSITES
MANUFACTURING TECHNOLOGY
The introduction of boron filaments in the early 1960s lead to the birth of advanced composites technology. High modulus, high strength continuous filaments, like boron and later carbon, have profoundly impacted today's aerospace airframe design and manufacturing. The application of boron/epoxy composites and the development of their manufacturing technology were limited by several factors: (1) the high cost of boron filament and no prospects for replacing expensive
tungsten substrate, (2) the limitation on a bend radius of no less than 1", (3) the high cost of diamond tools required for machining, drilling, and trimming, (4) the fact that the applications were limited to one form of prepregs (i.e., they were only available in 3" wide tape). Below is a summary of manufacturing techniques for boron/epoxy.
Most, if not all, were done by labor intensive hand layup on flat and moderately curved metal tools, using 3" wide tape (fabrics not available).
Extremely simple tools were used because of the bend radius limitation.
Hand-held tools with diamond tips and cutting edges were used for drilling and trimming.
Existing machines were used with diamond cutters for machining.
Crude automated tape layup (ATL) machines for 3" tape were available for R&D, but no production versions were developed.
Carbon and aramid fibers and prepregs were introduced in the latter 1960s. These fibers have some distinct advantages over boron: (1) their extremely small diameter (6 to 10 microns) reduced the
bend radius to less than 1/16", (2) traditional high-strength steel could be used instead of diamond-tip tools for cutting, trimming, drilling, and machining, (3) there was a greater potential
for achieving low cost ($10/lb compared to $90/lb for boron in 1960s dollars), (4) they were available in a variety of strengths, stiffnesses, and other mechanical properties. The introduction of
carbon fibers drastically increased the variety of applications and changed the way airframe structures were manufactured. Below is a list of manufacturing techniques and aids developed for carbon composites:
Many different kinds of fabrics and widths (some up to 60" wide) substantially increased the speed of hand layup processes. Drapeability was enormously helpful in the manufacturing of complex and concave products.
Tapes started to appear in 3, 6, 12, and 24 inch widths, which resulted in increased layup speeds.
Computer-controlled sophisticated ATLs began to appear in production. Improvements continue to this date. ATL can take different tape widths, and alignment becomes nearly perfect.
ACM (automatic cutting machines) flooded the market. These included the Gerber Cutter, ultrasonic, laser, and water jet machines. Improvements continue to this date.
The one-shot co-cured techniques using expandable mandrels became popular. Several different kinds of washable mandrels were also introduced. Some large structural boxes were made this way.
Non-metallic (especially graphite or carbon) tools also became popular.
Filament winding and braiding became possible with carbon and aramid fibers.
Sophisticated multi-angled ply orientation pultrusion machines appeared.
Research and development yielded tow placement, RTM (resin transfer molding), injection
molding, and other new manufacturing technologies.
Compression molding, diaphragm forming, hydroforming, magneforming, deepdrawing,
stamping, etc., began to appear in abundance.
Preforms and stitched preplies appeared
3-D and multi-directional weaving were used for improved damage tolerance and as
potential replacements for joints and fittings.
Thanks to the introduction and continuous improvements in carbon fiber and prepreg technology, a
quantum jump in progress was observed in advanced materials technology in general, and in
manufacturing technology in particular. It is expected that advanced composites technology will
continue to expand and improve. However, the rate and direction of expansion and improvement
may be quite different than what has been observed in the past. The primary reason for this
difference is the change in the driving forces of recent years.
When advanced composites technology was first introduced in the early 1960s, the emphasis was
on increased performance by means of reducing structural weight; very little attention was given
to low-cost manufacturing. The demand for high performance (reduced weight) was further aggrandized by the high cost of fuel which resulted from the oil shocks of 1973 and 1979. The well
known ACEE (Aircraft Energy Efficiency) program in the United States emerged from the fear of substantial increases in future fuel costs. The slogan was "reduced weight for reduced fuel cost."
To achieve high performance, some designs called for individually tailor-made plies which saved a mere ounce at a substantial cost penalty. Instead of the cost of fuel increasing as predicted, it has
actually dropped considerably (in real dollars) since the early 1980s, and the demand for high performance has somewhat diminished. Consequently, the ACEE program has lost much of its
funding and clout.
The advanced composites industry has begun to recognize that the potential market for composites
in commercial transport applications is much greater than that in military aircraft applications due
to the sheer size of commercial transport and its large production runs and rates. This has caused
the shift from military to commercial applications to accelerate in recent years.
The historical development of the Japanese composites manufacturing technology in the aerospace
industry dates back to the early 1970s, and follows closely that of the United States. give a quick review of past and present programs at Mitsubishi and Kawasaki Heavy
Industries. As can be seen in the charts, from 1970 to 1982 the composites work was largely
internally sponsored. The Japanese focus from the beginning was on primary structures. The bulk
of the subcontract work done in Japan for Boeing and Douglas during the 1980s was on control
surfaces and fairings. Despite the wishes of the Japanese to design and build composite primary
structures for the Boeing 777, the Japanese aircraft consortium instead received a contract for
metallic primary structures from Boeing.
CURRENT COMPOSITES MANUFACTURING
TECHNOLOGY
There is a general notion and confidence among the composites community that high-performance
all-composite aircraft can be designed and built using currently available manufacturing
technology if cost and schedule restrictions are ignored. The proof can be seen in such aircraft as
F-117, B-2, Starship, AVTEK 400, and Voyager.
Furthermore, composites have already proven their worth as weight-saving materials. Therefore,
the current challenge is not to make lighter-weight all-composite aircraft (a dream airplane
several years ago), but to make composite components economically attractive. The effort to
produce economically attractive composite components has resulted in several innovative
manufacturing techniques currently being used in the composites industry. It is obvious, especially for composites, that improvement in manufacturing technology alone is not enough to overcome the cost hurdle. It is essential that there be an integrated effort of design, material, process, tooling, quality assurance, manufacturing, and even program management for composites to become competitive with metals.
Nevertheless, for certain applications, the use of composites
rather than metals has in fact resulted in both lower cost and less weight. Some examples are cascades for engines, most of the compound curved fairings and fillets, replacements for welded metallic parts, cylinders, tubes, ducts, blade containment bands, and many more.
Resin Transfer Molding (RTM) Which is the actual technology being
employed by Foster Miller to produce the polymer:
This technology has a potential for cost reduction equal to that of fiber placement. The resin content requirement at 40% by volume also slows the process turnaround.
Research.
Aerospace applications of this technology are going in various directions. Cheaper preforms is one avenue. Lubricating the preforms to allow the mold to close over the bulk factor is
another major thrust. Tooling which has a larger volume during resin transfer and then seats to final position after filling is being pursued. Some research is actually targeting a structure as large
as a wing skin with stiffeners.
This material is now being offered in a thermoset matrix. The objective of this research is to find a suitable application for this material. It may have an application as inner stiffening
panels on doors and covers. It is also being considered for the web of tall beams to form corrugations or for stiffness.
The Japanese are familiar with long discontinuous fiber; however, no thermoplastic or thermoset projects were observed.
RELATED TECHNOLOGIES
Curing
The aerospace industry is primarily using autoclaves, ovens, and microwaves for curing. The use of
ovens and microwaves is somewhat confined to wet-wind missile production. Ovens are also used
to cure the so-called "room-temperature- cure" composite tools. Autoclaves are the primary
production curing tools for all users of prepreg.
Curing in Japan is generally performed using autoclaves. Few of the autoclaves observed by the
team had fully automated and programmable controls. One item of particular interest was the
close research tie between tooling and curing. Tool development makes full use of thin film
pressure transducers, dielectric resin viscosity sensors, and embedded thermocouples to produce
tool and cure processes which are reproducible.
Research. Autoclave research centers on improved control, critical parameter feedback
transducers, tool heating, and improved vacuum bags. The Japanese are working to eliminate the
need for autoclaves, researching techniques such as "cure-on-the-fly.
Tooling has more potential for improving part quality and reducing part cost than any other technological area. Tool design and part design are intimately linked. The key to success on a large
majority of the composite CRAD and IRAD programs is related to tooling. Tooling for aerospace composites could be considered a benchmark activity of its own.
FUTURE COMPOSITES MANUFACTURING
TECHNOLOGY
A major new breakthrough in composites manufacturing technology is not likely to occur in the foreseeable future. Most likely, there will be a series of improvements to existing manufacturing
technologies, and manufacturing concepts already generated will be proven. For composites to become competitive with metals, cost reduction has to occur in three areas: nonrecurring costs,
recurring costs, and direct operating costs (DOC) (e.g., durability, maintainability, reliability, and repairability). IPD will continue to infiltrate all the disciplines for improved efficiency in design
and manufacturing. It is expected that DOC will become a much bigger issue as many aircraft with composite components enter revenue service. There will be doubts as to whether composites will
ever become cost-effective for commercial use; however, these doubts can be assuaged by the facts. The reduction in manufacturing cost realized by improved technology will lose its value if it
is offset by an increase in nonrecurring costs and DOC. Thus, life cycle cost analyses should be conducted along with the traditional trade-off studies of weight vs. strength and stiffness vs. cost.
Improvements in automation, speed, variable thickness, pad-up insertion, consistent quality,flexibility in fiber orientation, control of resin and void content, and shapes other than cylinders
will be seen before more versatility appears in application. A combination of robotic and traditional filament winding (with seven to 10-axis) system is already available in crude form. If this system is perfected, it will be able to wind complex non-axisymmetric shapes, such as T and elbow shapes. One of the most critical requirements for a successful implementation of this method is controlling the tension of the deploying filament during the winding processes. This
critical problem may be quickly solved with the aid of powerful computers.
Hopefully it was informative.
Regards
Sri. |
