A computational investigation of the laser bonding of balloon catheters
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The balloon catheters produced by Boston Scientific are manufactured using a laser bonding process. The behaviour of the materials during this laser welding process is not very well understood. In this work a computational model of this process was created which will help predict the behaviour of the materials during bonding and will increase understanding of the laser bonding process. The two parts being bonded are cylindrical and are both made of a thermoplastic polymer called PEBAX®. During the bonding process, these cylindrical parts are surrounded by a heat-shrink tubing which applies a pressure to the PEBAX® parts when heated. The heat and pressure cause the PEBAX® to melt and flow. Modelling the heat-shrink tubing and the melt flow during the laser welding process are key aims of this work. A thermal model of the process was created by modelling the laser absorption and heat transfer through the assembly. This was compared with previous work and validated with experimental data. The PEBAX® was modelled as a viscoelastic material which transitions from relatively rigid to very compliant as it passes its melting temperature. Extensive experimental testing was performed to characterise the heat-shrink tubing. The heat-shrink tubing was modelled using two shape memory models from the literature. These two models were implemented into Abaqus FEA using two user defined material subroutines (UMATs). A thermo-mechanical finite element model of the bonding process was then created in Abaqus FEA and the results were compared with experimental data. This model captures the overall behaviour of the materials during the bonding process, providing predictions of melt flow. The results are compared with the experimentally observed melt flow providing new knowledge on the thermo-mechanical behaviour during the laser bonding process of balloon catheters.