Joining chemically incompatible materials for fused deposition modeling

Master thesis (2021)

Authors

K.J. van der Vlist Industrial Design Engineering

Contributors

Eugeni Doubrovski Sustainable Design Engineering (mentor)
Tim Kuipers Ultimaker (mentor)
Faculty
Industrial Design Engineering, Industrial Design Engineering
Copyright: © 2021 Klaas Jan van der Vlist
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Published Date

22-03-2021

Language

English

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Faculty

Industrial Design Engineering

Abstract

This report shows the development of a method that joins two chemically incompatible materials during Fused Deposition Modelling (FDM). State of the art FDM printers can extrude more than one material during the printing process. Due to chemical incompatibility of many polymers, the selection for combining materials is limited. This gives the following goal: “Generate a method to create a dual material object, made of two chemically incompatible materials during the FDM production process”. Studies related to multi-material FDM printing are discussed to find a starting point of this project. The use of a form interlocking shape to join the two chemically incompatible materials is chosen for further investigation. The concept is a form interlocking shape. This shape consists of rows of bridges made of polylactic acid (PLA, rigid material). Thermoplastic urethane (TPU, flexible material) is extruded under and around these bridges to create an interlocking shape. The PLA bridges are created using a non-planar printing approach. As opposed to the regular FDM process (planar), we created a continuous bead across multiple layers (non-planar). A prosthetic hand is created for demonstrating the method. The PLA main body and phalanges are connected with TPU links to allow bending of the fingers. We focused on the criteria: strength, applicability and process continuity. Based on these criteria, we made design choices regarding form interlocking shape, printing procedure and sequence, size and geometry and slicing software. We created specimens for determining the force-displacement relationship and used the peak force as a measure of the interface performance. The proposed concept (bridge pattern) is tested against two benchmarks: the overlapping feature available in slicer Cura (current industry standard) and an interlocking shape printed using a planar approach. Our proposed concept resulted in a higher peak force than the overlapping feature: 491N compared to 415N, an increase of 18%. The planar interlocking shape resulted in a peak force of 504N, even higher than our proposed concept. This production method is relevant for multi-material products manufactured with FDM. Examples are given of products in robotics and prosthetics, compliant mechanisms and wearables. The prosthetic hand was chosen as a demonstrator. A qualitative evaluation was performed on this prosthetic hand: using manual force only, neither the interface bond or the materials (PLA and TPU) could be broken. We have shown a method that creates a stronger bond (vertical interface) between two chemically incompatible materials (PLA and TPU) than the current industry standard.