Abstract: The matching of the expansion and pressurization of soft modes was the key to the soft molding of composites. In order to control the pressure of soft die in the process of soft die forming, the compression Poisson’s ratio, expansion behavior and pressure balance characteristics of soft mold were studied. The expansion and pressurization processes was demarcated into three steps, including free expansion, semi-free expansion and pressurization and volume-limited expansion and pressurization of soft mold. The deformation and pressure theory of different stages of soft modes were studied, and the size and pressure changes of soft modes was measured by soft mode heating system. The size of the soft die was designed based on the above theory, and the curing process was optimized. The C-beam and I-beam were fabricated by soft-mold forming technology, and the internal quality and dimensional accuracy were characterized. The experimental results show that the compression Poisson’s ratio of soft mold material is 0.495, and the expansion behavior and pressure balance characteristics of the soft modesare consistent with the theoretical analysis in different stages. The precise control of pressure in the process of composite soft die molding is realized through the size design and curing process optimization, and the C-beam and I-beam with excellent quality and high dimensional accuracy are successfully fabricated.

Key words: soft mold, Poisson’s ratio, expansion behavior, pressure balance, composite