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.

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:

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. Figures 1.1 and 1.2 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.


Figure 1.1. Major Composites Applications of MHI


Figure 1.2. Composite Products of Kawasaki Heavy Industries

Although numerous composite activities have taken place in the Japanese aerospace industry, the magnitude of those activities has been quite small when compared to that of the United States, as depicted in Table1.1.

Table 1.1
Carbon Fiber Usage in 1989

(tons)

It is evident from Table1.1 and Table1.2 that Japan's emphasis has been more on sporting goods and carbon fiber production than on aerospace. It is interesting to note that in Japan it was the textile industry (the world leader in the late 1950s and 1960s) which began the development and production of carbon fibers, whereas in the U.S. it was the chemical industry which took the initiative.

Table 1.2
Carbon Fiber Production Capability in 1991 (Pan & Pitch)

(tons)


Published: April 1994; WTEC Hyper-Librarian