Amol Ogale

• 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.