A Parametric Study for Tensile Properties of Silicone Rubber Specimen Using the Bowden-Type Silicone Printer

Abstract

Silicone printing can enable a lot more accessibility and customizability towards utilizing silicone in different applications, including medicine for its biocompatibility. However, challenges existed for printing in specific geometries due to the lack of guidelines and studies on the mechanical properties. To support the understanding of printing three-dimensional silicone structure having different infill patterns and gel-like material, this paper conducted a parametric study for the specimens printed using a Bowden-type silicone printer and measurements of the tensile properties. Four printing parameters of print speed, infill density, flow rate, and infill pattern, are categorized following the Taguchi L9 method, and arranged into the four-parameter-three-level orthogonal array. The signal-to-noise (S/N) ratio was calculated based on the principle of the-larger-the-better, and analysis of variance (ANOVA) was also obtained. Tensile performance was further discussed with the characterization of internal structure, using the cross-sections of the printed specimens. It was found that the change of flow rate is the most significant to the tensile stress; and for the tensile strain, infill pattern was found to be the most significant parameter. The Line infill pattern consistently presented the highest tensile stress. Agglomeration can be seen inside the printed structure, hence optimal printing parameters play an important role for complicated geometry, while ensuring the flow rate and infill density do not exceed a reasonable value. This study would serve as the guideline for printing three-dimensional silicone structures.

Keywords: parametric study; silicone printing; taguchi method; tensile properties.

Figure 1

(A) A schematic diagram of the printing mechanism; and (B) a photo of printing the silicone dumbbell specimens.

Figure 2

(A–C) The shapes of the sliced preview image of the (A) Grid, (B) Line, and (C) Concentric infill patterns used in the study. (D–F) The resulting (D) Grid, (E) Line, and (F) Concentric infill patterns printed by the silicone printer. These are all printed at 60 mm/s and at a 53% infill density to visually show the intended patterns.

Figure 3

The photos of (A) printing the first layer of the dumbbell specimen; (B) the cured dumbbell specimens in one combination group.

Figure 4

An example of (A) engineering stress-strain curves; and (B) true stress-strain curves of the combination 5 for repeatability.

Figure 5

Summary of the average maximum values and standard deviations of (A) engineering strain; (B) engineering stress; (C) true strain; and (D) true stress of all combinations.

Figure 6

Line graphs of the effects of print parameters on the (A) maximum engineering stress in MPa; (B) maximum true stress in MPa; (C) engineering stress S/N ratio; and (D) true stress S/N ratio.

Figure 7

Line graphs of the effects of print parameters on the (A) maximum engineering strain; (B) maximum true strain; (C) engineering strain S/N ratio; and (D) true strain S/N ratio.

Figure 8

Silicone-printed specimens grouped according to their combination number as well as their printing parameter values. The red boxes indicated where the sliced cross-section is located. (A) Combination 1: Print speed: 10 mm/s; Infill density: 15%; Flow rate: 50%; Infill pattern: Grid. (B) Combination 2: Print speed: 10 mm/s; Infill density: 53%; Flow rate: 75%; Infill pattern: Line. (C) Combination 3: Print speed: 10 mm/s; Infill density: 90%; Flow rate: 100%; Infill pattern: Concentric. (D) Combination 4: Print speed: 35 mm/s; Infill density: 15%; Flow rate: 75%; Infill pattern: Concentric. (E) Combination 5: Print speed: 35 mm/s; Infill density: 53%; Flow rate: 100%; Infill pattern: Grid. (F) Combination 6: Print speed: 35 mm/s; Infill density: 90%; Flow rate: 50%; Infill pattern: Line. (G) Combination 7: Print speed: 60 mm/s; Infill density: 15%; Flow rate: 100%; Infill pattern: Line. (H) Combination 8: Print speed: 60 mm/s; Infill density: 53%; Flow rate: 50%; Infill pattern: Concentric. (I) Combination 9: Print speed: 60 mm/s; Infill density: 90%; Flow rate: 75%; Infill pattern: Grid.

Figure 9

Cross-sectional images captured by Olympus SZX7, their ideal results, and their corresponding printing parameters. (A) Combination 1: Print speed: 10 mm/s; Infill density: 15%; Flow rate: 50%; Infill Pattern: Grid. (B) Combination 2: Print speed: 10 mm/s; Infill density: 53%; Flow rate: 75%; Infill pattern: Line. (C) Combination 3: Print speed: 10 mm/s; Infill density: 90%; Flow rate: 100%; Infill pattern: Concentric. (D) Combination 4: Print speed: 35 mm/s; Infill density: 15%; Flow rate: 75%; Infill pattern: Concentric. (E) Combination 5: Print speed: 35 mm/s; Infill density: 53%; Flow rate: 100%; Infill pattern: Grid. (F) Combination 6: Print speed: 35 mm/s; Infill density: 90%; Flow rate: 50%; Infill pattern: Line. (G) Combination 7: Print speed: 60 mm/s; Infill density: 15%; Flow rate: 100%; Infill pattern: Line. (H) Combination 8: Print speed: 60 mm/s; Infill density: 53%; Flow rate: 50%; Infill pattern: Concentric. (I) Combination 9: Print speed: 60 mm/s; Infill density: 90%; Flow rate: 75%; Infill pattern: Grid.

Figure 10

(A) Cross-sectional images captured by Olympus SZX7; (B) image process via MATLAB; (C) the resulting segmented area ratio error for each combination. Line graphs of the effects of print parameters on the segment ratio error in terms of (D) mean response, and (E) S/N ratio response.