Additive manufacturing of high pressure hydraulic seals

Abstract

This project is a collaboration between the University of Malta and Trelleborg Sealing Solutions Malta. The main aim of this project is to develop a high pressure hydraulic seal by the use of additive manufacturing. A high temperature FDM printer was chosen for the production of the hydraulic seal which are to be produced from a high performance engineering polymer known as PEEK. To achieve this goal, thorough research on the material and on both common and high temperature 3D printing was performed. Furthermore, the default printing profile of the printer was used for the development of the first seal to understand better the state of printing. The seal was tested on a test jig but failed after a number of cycles. Upon analysis, the seal showed several defects such as delamination, shrinakage and inconsistent wear. This meant that the process is not yet optimized for production. A set of parameters namely the ‘Nozzle Temperature’, ‘Extrusion Multiplier’, ‘Extrusion Width’, and ‘Layer Height’ were chosen to be studied within a defined range in order to come up with the optimal printing profile. A set of printing profiles were created using combinations of the aforementioned parameters. These were tested against each other through a DMA test and a shear test; the profile which obtained highest results and lowest deviation was chosen as the optimum profile. The extrusion multiplier, layer height and nozzle temperature had the greatest effect in increasing strength. The new state of the process was tested by testing the performance of the new printed test specimens. DMA, Compression, hardness, tensile and DSC testing were performed as these will reflect the properties of the final seal to be produced. In most tests the printed showed poorer performance when compared to the machined specimens. Nevertheless, the results show great potential that the current state may still be used for the production of functional parts. The optimised printing profile was then used for the development of the hydraulic seal. Dimensional errors were reduced when printing with the optimized profile. Slight modifications were done to the CAD model in order to compensate for shrinkage and ease the manufacturing process. A small batch of seals were produced and measured to see whether any further modifications were required until the dimensions fit within tolerance.