Study on Efficient Fused Deposition Modelling of Thermoplastic Polyurethane Inflatable Wall Features for Airtightness

Abstract

The thermoplastic polyurethane (TPU) material is an elastomer that can be used for inflatable products. Fused deposition modelling (FDM) is a widely used additive manufacturing process for TPU material due to the capability of generating complex structures with low cost. However, TPU is soft and thus difficult to be extruded as continuously and uniformly as hard materials such as polylactide by FDM. Inappropriate extruder structure and speed settings can lead to filament buckling problem, resulting in poor material filling quality, long printing time and low printing success rate. This paper aims at improving the FDM printing efficiency of TPU inflatable products by adding lateral support to the filament and finding out the appropriate speed ranges for different wall features and thicknesses. Firstly, a filament guide sheet is designed as being inserted into the gap between the drive gears and the bottom frame of the gear chamber in order to prevent the soft TPU filament from buckling. Secondly, inflatable product wall features are classified into floors, roofs and sidewalls and experiment for finding the relationship between printing speed and airtightness is carried out. In order to verify the proposed solution, wall features are printed and the material fillings obtained under different printing speeds are compared by measuring the airtightness of the wall features. Results show that the proposed filament guide sheet mitigates filament buckling, and the speed range that meets the airtightness requirement can be found for various wall features and thicknesses. In summary, the sealing of the filament feeding channel between the drive gears and the nozzle, as well as the speed optimisation according to product features, are essential for the efficient printing of TPU inflatable products.