Strengthening of 3D printed fused deposition manufactured parts using the fill compositing technique

Abstract

In this paper, we present a technique for increasing the strength of thermoplastic fused deposition manufactured printed parts while retaining the benefits of the process such as ease, speed of implementation, and complex part geometries. By carefully placing voids in the printed parts and filling them with high-strength resins, we can improve the overall part strength and stiffness by up to 45% and 25%, respectively. We discuss the process parameters necessary to use this strengthening technique and the theoretically possible strength improvements to bending beam members. We then show three-point bend testing data comparing solid printed ABS samples with those strengthened through the fill compositing process, as well as examples of 3D printed parts used in real-world applications.

Fig 1. Fingers of the i-HY hand are made using fill compositing to add strength to the 3D printed components.

The red (dark) portion illustrates the internal reinforcing structure of the 3D printed part.

Fig 2. ABS material exhibits a large variation in flexure strength based on print orientation and printer parameters.

I) upright print with raster infill, II) vertical print with raster infill, III) horizontal print with raster infill, IV) vertical print with multiple contours, V) horizontal print with multiple contours, VI) sparse-fill vertical print, VII) sparse-fill horizontal print.

Fig 3. The process of fill compositing uses the original part geometry but takes advantage of voids designed into the printed component which are filled with higher-strength resin.

The process is illustrated here with the proximal link of the i-HY [28] robot finger.

Fig 4. The calculated maximum bending moment for the various fill-composite cross-sections shows the ability to increase the capable bending load by 25% or reduce the mass of the beam by 33% using fill compositing with Epoxy resin.

Fig 5. Flexure stress comparison of three common resins with and without wollastonite additive.

The black x indicates the location of failure and the black circle represents the 0.2% yield strength.

Fig 6. Flexure strength of 105–206 epoxy filled samples printed with various types of sparse infill.

The black x indicates the location of failure and the black circle represents location of 0.2% yield strength. a) Insight hexagonal porous infill, b) Insight default sparse infill c) Designed sparse infill. The (v) or (h) indicates if the part was printed in the vertical or horizontal orientation.

Fig 7. Cross-sections of the tested samples including the raw material cast samples, and the solid printed ABS samples.

a) West systems 105–206 Epoxy, b) Epoxy filled hollow shell, c) Hexagonal porous infill, d) Insight default sparse infill, e) Designed sparse infill, f) Epoxy filled channels, g) solid printed ABS. All the above images are of 105–206 epoxy but the same samples were made with the IE-3076 urethane with wollastonite additive.

Fig 8. Flexure strength of epoxy filled shells made using fill compositing as compared to solid printed ABS in various orientations.

The test samples are labeled according to the cross-section image in Fig 7. The black x indicates the location of failure and the black circle represents location of 0.2% yield strength.

Fig 9. Flexure strength to weight ratio of solid ABS samples compared to those manufactured using fill compositing.

As a control, samples were also tested that were printed the ABS in the same geometry as the epoxy filled channel samples.

Fig 10. The flexure strength of the fill-composite sample using IE-3076 Urethane with wollastonite additive showed a large increase in stiffness over solid printed ABS samples.

The letter labeling indicates the cross-section of the sample as illustrated in Fig 7. The solid printed ABS samples are shown for all printed orientations.

Fig 11. Cross-section view of the robotic components (left) proximal joint of the robot finger, (right) spokes and outer ring of the wheel.

1) Solid printed ABS, 2) 1mm channels filled with epoxy, 3) Hollow printed shell filled with epoxy.

Fig 12. Images of testing setup on an Instron Testing system to measure failure loads of the robot finger proximal joint (left) and a simple robot wheel (right).

Fig 13. Comparison of robotic finger link strength shows improvement in failure strength using a 3D printed shell of the same part geometry filled with epoxy resin.

The black x shows the point of failure.

Fig 14. Comparison of wheel strength shows a 45% increase in load capacity using fill compositing with epoxy resin versus a solid printed ABS component.

The black x shows the point of failure.

Fig 15. The cross-sections of a printed open-end wrench that have been strengthened with fill compositing are shown in the bottom right.

a) Solid printed ABS, b) Designed sparse fill with IE-3076 with wollastonite additive, c) Hollow channels filled with IE-3076 with wollastonite additive, d) Hollow print filled with IE-3076 with wollastonite additive. The top plot shows the torque and rotational displacement of each sample during destructive testing.