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Sewn net-shape preform based composite manufacturing technology is widely
accepted in combination with liquid composite molding technologies for the
manufacturing of fiber reinforced polymer composites. The development of threedimensional
dry fibrous reinforcement structures containing desired fiber orientation
and volume fraction before the resin infusion is based on the predefined preforming
processes. Various preform manufacturing aspects influence the overall composite
manufacturing processes. Sewing technology used for the preform manufacturing
has number of challenges to overcome which includes consistency in preform quality,
composite quality, and composite mechanical properties.
Experimental studies are undertaken to investigate the influence of various sewing
parameters on the preform manufacturing processes, preform quality, and the fiber
reinforced polymer composite quality and properties. Sewing thread, sewing machine
parameters, shortcomings of sewing process, and remedies are explained according
to their importance during preforming and liquid composite molding. The stitches and
fiber free zone in the form of ellipse that are generated in the thickness direction were
investigated by evaluating the laminate micrographs. Correlation between ellipse
formation phenomenon, sewing thread, and sewing machine parameters is
established. A statistical tool, analysis of variance, was used to emphasize the major
preform processing factors influencing the preform imperfections.
For assessing the preform quality, the observations of sewing thread requirements
for preform and structural sewing were well documented during the experimental
studies and explained according to their significance in the composite processing.
Furthermore, selection criteria for sewing thread according to end application are
discussed in detail. Investigations on polyester sewing thread as a high speed
preform manufacturing element are also performed. Applicability of polyester sewing
thread for the preform sewing and challenges to be overcome for its extensive
utilization in the composite components are explained. Apart from this, influence of
physical structure of sewing thread on the laminate quality and properties are
explained and relationship between them is discussed in brief. Furthermore,
challenges caused due to applied spin-finishes and sizing and remedies for the same
are discussed. Sewing threads made of high performance fibers that are available in the market,
e.g., carbon, glass, and Zylon are studied for effect of thread material on through-thethickness
laminate properties. Threads made up of carbon or glass fibers are very
rigid and produces number of defects, which is a major cause of concern. Optimized
sewing procedure has been implemented to minimize the in-plane and through-thethickness
imperfections and to improve mechanical properties and surface
characteristics of composite laminate.
Preform sewing process and final ready to impregnate preforms were analyzed for
quality appearance. The sewing defects and their influence on composite structure
are monitored. Preform compressibility before and after the sewing operations are
intensively studied and correlation with sewing parameters is developed. Influence of
sewing process parameters on the warpage and change in preform area weight are
also explained in detail. Results of analytical experiments can help to improve further
exploitation of sewn preforms for composite manufacturing and overall preform and
laminate quality.