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Machine control data for the automation of the circular braiding process has been generated using previously published mathematical models that neglect yarn interaction. This resulted in a significant deviation from the required braid angle at mandrel cross-sectional changes, likely caused by an incorrect convergence zone length, in turn caused by this neglect. Therefore the objective is to use a new model that includes the yarn interaction, assuming an axisymmetrical biaxial process with a cylindrical mandrel and Coulomb friction. Experimental validation with carbon yarns and a 144 carrier machine confirms a convergence zone length decrease of 25% with respect to a model without yarn interaction for the case analyzed, matching the model prediction using a coefficient of friction of around 0.3.

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Pressure vessel manufacturing is currently dominated by the filament winding process. When higher production rates are required, circular braiding can be considered as an alternative because hundreds of yarns are deposited simultaneously from interlacing spools. The process has a high repeatability and is suited for automated series production, as is currently shown with the production of a-pillars and rockers in the automotive industry. Important manufacturing constraints related to the overbraiding of cylindrical pressure vessels are to avoid excessive jamming of the braid, typically occurring at a small mandrel radius, and to achieve a 100% cover factor at the largest mandrel diameter. In this paper, design guidelines for braiding of cylindrical pressure vessels are proposed. It is shown that a proper choice of the yarn cross-sectional area size and of yarn width-to-thickness aspect ratio can improve the design feasibility, but an adjustment of the braid angle can be required as well.

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