Abstract: This article introduces the design and produce process of stainless mold for composite tubes made by inflatable bladder by using silicone circular tubes as the bladder for pressure. Meanwhile, different carbon composite circular tube under different designed process gaps were fabricated. The micro appearance of the circular tubes section was observed by metalloscope. The compressive properties of the circular tubes were tested, and the mechanical properties results were compared with the plate by the autoclave, which were molding with the same materials and the curing cycle. The results show that, under such forming process, the quality of this product is best. When the ratio of the process gap and the designed thickness of the circular tubes is 34%, the monolayer thickness is relatively lower and uniform, and there are few defects in the tube wall inner. The compressive strength is 634 MPa which is equivalent to the one made by autoclave molding with a compressive strength of 647 MPa. The forming quality and the compressive strength were reduced with the increase of the process gap. Significantly delamination,porosity and defects were shown when the process gap ratio is 86.7%. Meanwhile, the monolayer thickness became larger and uneven. The compressive strength is 427 MPa, which was reduced by 34% compared with the highest value. Forming properties and compressive strength will show the decreased trend when the process gap was reduced, however, it is not significant.

Key words: composites, carbon fiber, inflatable bladder molding, circular tube, process gap