Abstract
Thermoforming of braided thermoplastic composite tubes was carried out in order to clarify the mechanism of thermoforming process for pipe fittings such as T-shape fittings, cross fittings and three dimensional fittings. The composite tube was made of cowoven braid that consists of carbon braid and polyamide resin, and the tubes with 4-ply and initial fiber orientation 18 and 26 degrees are used in the experiment. The tube set up in a molding die was formed using internal pressure by compressed air up to 0.7 MPa under nearly melting point of the matrix. Fiber orientation, wall thickness, axial reduction and branch height after the forming are measured in order to examine the forming characteristics. The branch is formed with not only the fisherman's net effect but also with moving yarns along longitudinal direction in every forming. The results show that deformation behavior of braid is very complex. Therefore, fiber orientation through the forming is also greatly changed. As a result, the height of branch can be obtained up to 20mm in T-shape fitting. Wall thickness at branch decreases with increasing height of branch. In particular, thickness is very thin near the top of branch. Axial reduction of tube varies in circumferential direction. From these results, it is found that the complex shape fitting can be produced by thermoforming. T-shape fitting, cross fitting and three dimensional fitting are achieved by this process. It is confirmed that moving yarns along longitudinal direction plays an important role in branch forming of pipe fittings.
