Characteristics of expert in stacking process for autoclave molding

Many of the prototypes of carbon fiber-reinforced composite materials are made by technicians with their hands, using the autoclave molding. Autoclave molding is a molding method where 1) carbon fiber that is impregnated with a resin, called prepreg is laminated in a forming die, 2) bagging is performed with bagging films (vacuum and deaeration packaging materials), 3) air and volatiles contained in the bagging film are removed under vacuum, using a kiln (autoclave), simultaneously 4) the prepreg is heated, pressurized, and set. Because the molding method is all manual work, instruction manual is necessary not to cause individual differences to occur. However, there is no curriculum for workers to acquire necessary skills to overcome the difficulty of quality management, and there is no system to clearly evaluate the level of the skill. Furthermore, there is no literature that clarifies the instructions for the manual work process and molding tools. Therefore, in the manufacturing sites, defectives products have been produced by technicians with less experience. The objective of this study was to clarify the characteristics of skilled technicians in the prepreg lamination process of autoclave molding. We recorded video of the prepreg laminating process, and conducted work analysis. Furthermore, we interviewed skilled technicians in order to clarify the purpose of each work process. As a result, in the corner laminating, skilled technicians improved the adhesion of the prepreg sheet to the forming die and accurately cut the prepreg sheet using scissors, by folding the prepreg sheet, just like they fold origami, in order to crease the prepreg sheet. Furthermore, by minimizing the use of dryer, they improved formability and prevented unnecessary prepreg sheet from sticking, while controlling the heat softening and stickiness.