40207_16 - H AND LAY-UP AND BAG MOLDING D .R. Sidwell 16...

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HAND LAY-UP AND BAG MOLDING 16 D.R. Sidwell 16.1 INTRODUCTION This chapter presents practical fabrication and tooling methods that have been successful for high performance applications. Increasing per- formance requirements limit traditional hand (’wet’) lay-up methods. Today’s prepreg resin systems allow for longer working life and low cure temperatures. Improvements have made the current prepreg systems the choice for high performance composite structures. Composites are a combination of a high performance resin matrix and various fiber combinations, which have brought about a change in the engineer’s traditional approach and allow matrix alloying for specific struc- tural applications. Improved materials, analysis and manufacturing methods have let traditional composite structures reach new limits of achievement. Table 16.1 presents some of the advantages and disadvantages of hand lay-up of composite structures. Composite structures have been manufac- tured from fiberglass and wood to some of the most expensive 800 GPa pitch fibers for space applications. The engineer’s imagination is the only limitation in the fabrication of composite structures. Large, complex co-cured structures are successfully manufactured with all engi- neering and manufacturing disciplines working as one. In the fabrication of wood or metal prod- ucts, flat sheet stock is joined together to form Handbook of Composites. Edited by S.T. Peters. Published in 1998 by Chapman & Hall, London. ISBN 0 412 54020 7 Table 16.1 Advantages and disadvantages of hand lay-up structures Adva n tages Design flexibility Large and complex items can be produced Minimum equipment investment is necessary Tooling cost is low The start-up lead time and cost are minimal Design changes are easily effected Molded-in inserts and structural reinforcements Sandwich constructions are possible Proto-typing and pre-production method for Semi-skilled workers are needed, and worker are possible molding processes training is minimal Disadvantages The process is labor-intensive Only one tooled (molded) surface is obtained Quality is related to the skill of the operator It is a low-volume process Longer cure times required The waste factor can be high a structural part upon which the external paint finish is applied. The reverse of this procedure occurs with composite materials fabrication, where the formless materials harden and take the shape of the container into which they are applied. The makeup of the resulting laminate is an elementary engineering material. The physical properties can be changed by varying the resin and fiber ratio, the type and direction of reinforcement and the type of resin matrix. Today bag molded (vacuum and pressure) composites provide higher performance and
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Histoy 353 are competitive with alternate types of con- structions that result from optimization of process controls, design refinements and improved materials. Composite designs and bag molding processes are interrelated by pro- duction goals, the desire to control
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40207_16 - H AND LAY-UP AND BAG MOLDING D .R. Sidwell 16...

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