Comparative study of the tensile properties of fibre reinforced additively manufactured and injection moulded components
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Παπαχαράλαμπος, Σωτήριος
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Abstract
The objective of any industry is to provide a product to the consumer in the most efficient manner, beginning with the initial concept and concluding with the final consumer good. The rise of Additive Manufacturing and its integration into the industrial environment presents a compelling avenue for investigation in a segment traditionally dominated by Injection Moulding. Each method possesses dis-tinct advantages, with the most important being the manufacturing flexibility offered by Additive Manufacturing, which is ideal for prototyping, and the low cost of Injection Moulding for large-scale manufacturing. Limitations of each method can be addressed by the opposite method, respectively. This statement indicates that Additive Manufacturing is not suited to replace Injection Moulding but raises the question of how the individual advantages of the processes can be combined to reduce the cost and time spent in the development stages of a product.
The use of Additive Manufacturing is currently focused on on-demand production and custom de-signs, as well as prototyping in order to check dimensional properties of a product. The objective of this work is to introduce a new dimension to the current trend by providing high-demanding segments such as automotive and civil engineering with an additional control point before production, which is currently supported only by simulation.
The rationale behind this research is to investigate the relationship between Injection Moulding and Additive Manufacturing. To this end, the mechanical properties of parts produced by each method will be examined. The material selected is a fibre-reinforced polyamide polymer, which is a type of material commonly used in demanding applications that require high mechanical properties. The re-sults provided by the mechanical investigation of the specimens provide an insight of the influence of each method to the behaviour of the material and the ability to establish a transfer function that can provision the behaviour of an Injection Moulding product, by testing the prototype produced with Addi-tive Manufacturing.
In order to directly and accurately compare the processes of Additive Manufacturing (AM) and In-jection Moulding (IM), both production methods must be able to process the same raw material and manufacture a wide range of geometries. This is necessary in order for the resulting products to be applicable in an industrial environment. The objective is achieved through the use of extrusion-based Additive Manufacturing, which employs an extruder that can process polymeric material in the form of pellets, which is typically employed in Injection Moulding. The extruder is connected to a six-axis in-dustrial kinematic system, which provides precise positioning over a large area.
Using both Additive Manufacturing and Injection Moulding, 1BA tensile-test specimens are pro-duced and tested. The specimens are taken from different angles relative to the direction of deposi-tion or direction of flow to identify the effect of anisotropy that characterizes fibre reinforced polymers and the two production methods.
The data collected from tensile testing include the ultimate tensile strength, tensile modulus, and elongation of the specimen, providing an important insight into the influence of the production method and the reinforcement of the material to the behaviour of the specimens. Later, the tested specimens are investigated at the area of fracture using field emission scanning electron microscopy (FESEM).
The results conducted by the tensile testing and microscopy investigation provide a number of con-clusions about the correlation of the two methods and the behaviour of them when a fibre reinforced polymer is employed. The tensile testing results indicate the existence of anisotropic behaviour in both methods which can be linked to the fibre alignment of the composite and the structural characteristics of the specimens in microscopy testing.
In more detail, both Additive Manufacturing and Injection Moulding provide high alignment with the direction of deposition and direction of flow. Although both processes provide comparable me-chanical properties when loaded in this direction, the anisotropic behaviour of Additive Manufacturing specimens results in lower tensile strength in directions deviating from the direction of deposition. Analyses of microscopy images of Additive Manufacturing specimens in directions other than the dep-osition direction have revealed that the fracture occurs between layers, indicating a weakness in in-terlayer adhesion. Furthermore, microscopic analysis has revealed the presence of strand separation and air voids in specimens manufactured using the Additive Manufacturing process. These defects have been demonstrated to have an impact on the mechanical properties of the specimens.
The total of tensile testing results indicates the influence of each component of the composite. In the direction parallel to the alignment of the fibres, the composite exhibits high stiffness, which is typi-cal of reinforcing materials such as glass fibre, which is used in this case. In the direction orthogonal to the alignment of the fibres, the composite displays a more ductile behaviour, indicating that the me-chanical load is primarily absorbed by the polymeric matrix.
As an overview, Additive Manufacturing provides great flexibility, with low initial cost, making it ideal for prototyping, while Injection Moulding offers high-quality and low costs for mass production, with a significantly expensive and time-consuming development stage. The results of this work suggest by understanding the differences of the two methods, Additive manufacturing can be used for proto-typing to further ensure the estimations provided by simulation. This way, the initial cost and time needed for the development stage of a product manufactured by Injection Moulding can be further reduced.
The same procedure is suggested to be applied for a wider range of orientation in both methods, including a variety of materials and more complex geometries, as well as using other deposition tech-niques that reduce the effect of anisotropic characteristics due to the production method.
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Keywords
Additive manufacturing, Injection moulding, Reinforced polymers, Tensile properties, Tensile strength