Investigation of a Short Carbon Fibre-Reinforced Polyamide and Comparison of Two Manufacturing Processes: Fused Deposition Modelling (FDM) and Polymer Injection Moulding (PIM)

Abstract

New technologies are offering progressively more effective alternatives to traditional ones. Additive Manufacturing (AM) is gaining importance in fields related to design, manufacturing, engineering and medicine, especially in applications which require complex geometries. Fused Deposition Modelling (FDM) is framed within AM as a technology in which, due to their layer-by-layer deposition, thermoplastic polymers are used for manufacturing parts with a high degree of accuracy and minimum material waste during the process. The traditional technology corresponding to FDM is Polymer Injection Moulding, in which polymeric pellets are injected by pressure into a mould using the required geometry. The increasing use of PA6 in Additive Manufacturing makes it necessary to study the possibility of replacing certain parts manufactured by injection moulding with those created using FDM. In this work, PA6 was selected due to its higher mechanical properties in comparison with PA12. Moreover, its higher melting point has been a limitation for 3D printing technology, and a further study of composites made of PA6 using 3D printing processes is needed. Nevertheless, analysis of the mechanical response of standardised samples and the influence of the manufacturing process on the polyamide's mechanical properties needs to be carried out. In this work, a comparative study between the two processes was conducted, and conclusions were drawn from an engineering perspective.

Keywords: 3D printing; CFRP; additive manufacturing; composites; fused deposition modelling; polyamide; polymer injection moulding.

Figure 1

Stereomicroscope images (×1.25) of the appearance of the injected and different patterned printed samples.

Figure 2

Results of the fibre length distribution in the raw material, injected and printed samples (A) and measurement of diameters in fibres using 400× with a microscope (B).

Figure 3

The DSC analysis of the samples printed at different built plate temperatures to analyse the influence of the thermal environment on the degree of crystallinity. The DSC analysis of raw material is shown in (A), the top parts are the analyses shown in (B) and the bottom parts are the analyses shown in (C).

Figure 4

Positioning samples in the bending test, labelled (top and bottom) according to printing placement.

Figure 5

Analysis of the mechanical response of the samples manufactured by 3D printing at different build plate temperatures to study if anisotropy was caused by the thermal environment. (A) Build plate temperature: 110 °C, (B) build plate temperature: 60 °C, (C) build plate temperature: 25 °C and (D) bending test comparison of (A–C).

Figure 6

Tensile test. Results obtained for Young’s Modulus, yield strength and tensile strength of the injected and 3D printed samples.

Figure 7

Comparison of the behaviour of the injected and printed samples with stretching stresses in the tensile test (A), and the influence of infill density and printing pattern on the mechanical behaviour of the printed parts (B).

Figure 8

Fractographies of tested tensile samples: (A) Injection moulding 600×; (B) injection moulding 1000×; (C) 3D printed unidirectional 0° 600×; (D) 3D printed $\pm 45°$ 600×.

Figure 9

Compression test. Results obtained for yield strength, tensile strength and Young’s Modulus of the injected and 3D printed samples.

Figure 10

Fracture images of samples under compressive stress. (A) Unidirectional 100%, (B) unidirectional 60%, (C) triangles 60% and (D) linear $\pm$45. (E) Comparison between the injected and printed samples in the compression test.

Figure 11

Compression test: influence of pattern on the behaviour of sample under compressive stresses.