Mechanical characterisation of anisotropic silica sand/furan resin compound induced by binder jet 3D additive manufacturing technology
Introduction
Additive manufacturing technologies are commonly used because of their ability to produce geometrically complex parts [1,2]. Originally, this process was used for rapid prototyping, which significantly reduced investment in earlier manufacturing processes. As the accuracy of the parts obtained from this process has improved, their application has expanded to rapid prototyping and manufacturing [[3], [4], [5], [6]]. Some studies [7,8] have made the use of this technique to produce final pieces. Today, there is a wide variety of additive manufacturing techniques. In the market, the choice of such technology requires a good understanding of each one and the multi-physical issues associated with their use.
Existing several 3D printing techniques include stereolithography (SLA) [[9], [10], [11]] selective laser sintering (SLS) [[12], [13], [14]] and fused deposition modeling (FDM) [[15], [16], [17], [18]]. Recently, a new 3D sand printing technique has been proposed to produce complete mould parts and assemblies for foundry applications [[19], [20], [21], [22], [23], [24]]. The 3D sand printing technique is considered a cost-effective moulding process [25] and can be used with a wide variety of materials [26]. This process is based on inkjet printing technology [27,28] and has been used for the production of metal and ceramic structures. This process is similar to other powder-based techniques and uses an inkjet print head to spray the binder onto the construction area. Recently, ExOne TM developed this system to make sand moulds by applying binder projection technology. The ExOne sand 3D printing technology is seeing more use as it significantly reduces mould design time from a digital model (CAD) in a layer-by-layer mode [29,30] and allows pieces with complex geometries to be made. The mechanical properties of the ExOne sand 3D printed parts are unknown because many process parameters that can affect their properties [31]. In addition, because of the porous nature of the printed structures, the functional mechanical properties of the parts at the end of testing are very dispersed and difficult to reproduce. Some studies have been carried out to identify the impact of different parameters of the ExOne sand 3D printing process on the mechanical performance of the processed parts [[30], [31], [32]]. Coniglio et al. [31] evaluated the influence of the printing orientation, print resolution, recoating speed and sample positioning in the job box on the 3-point bending strength and permeability of the parts made from the process. The authors showed that the recoating speed simultaneously influenced the flexural strength and permeability of the parts, while the print resolution only affected their respective flexural strength. Gill et al. [33] have revealed that the amount of binder in each part can modify their mechanical properties. Indeed, the parts produced by this method retain the moisture generated by the binder crosslinking reaction, which affects their mechanical properties in particular, their compressive strength values. More recently, the influences of binder content on the flexural strength and mass transport properties of each part have been discussed [30]. The authors proved that the flexural strength of the printed parts is very dependent on their respective binder content values and the curing methods used to produce them. On the contrary, the impact of the binder content on the initial permeability of the samples before curing was negligible. Mitra et al. [9] have studied the effects of hardening temperature and aging time on sample flexural strength and permeability. Their results have shown that the printed parts can be stored at room temperature for a long time before being used, which considerably preserves their mechanical properties such as their flexural strength under 3-point bending. The mechanical results obtained by these studies, however, show a wide dispersion, which degrades the reliability in designing functional 3DSP moulds. This dispersion can be introduced through the 3-point bending flexural test setup. In fact, the testing technique involves a sample fixture with three supporting pins (two fixed and one mobile). During the test, the printed specimen was locally probed by these pins, particularly in the zone where the mobile pin is located (Fig. 1). Due to the porous nature of the ExOne printed ceramic part, the probed zone could be rich in silica or porosity. In the case that the region beneath the mobile supporting pin exhibits a highly porous area, the samples mechanical properties will be considerably lower than instances when the region is compacted by silica particles. In other words, the elementary volume subjected to loading under the pin does not represent the microstructure of the overall sample. Consequently, the effects of the printing conditions by selecting this representative elementary volume (REV) located near the supporting pin no longer become relevant.
Some authors propose other techniques for characterising the mechanical properties of ExOne printed samples [34,35]. Vogler et al. have characterised the mechanical properties of artificial sandstone, created by 3D additive manufacturing technology, via the indirect tensile strength method. The authors verified the failure mode of printed specimens by using digital imaging techniques.
This study aims to characterise printed parts by analysing the individual impact of the various parameters of the sand 3D printing process on the performance of manufactured products under static stress. The mechanical characterisation of the test specimens was performed using uniaxial compression tests. For this purpose, a specific device has been made to assess the mechanical properties. The use of this anti-buckling device during the compression tests requires specimens of specific dimensions. The printed test pieces were double notched to initiate cracking in a predefined area, which makes it possible to focus on the rupture zone and to improve the reproducibility of the results. Mechanical characteristics such as elongation at break and ultimate failure load are determined by this technique. The effects of manufacturing parameters such as print orientation and building direction on the compression properties of the printed samples were rigorously studied. Microstructural observations make it possible for pore-size distributions to be derived and to comprehend the relationship between the manufacturing process and the part's final mechanical properties.
Section snippets
Experimental methodology
In this paragraph, the material, equipment, and conditions used in the production and mechanical characterisation of the specimens are described in detail.
Compressive properties of preliminary 3DSP samples
In order to establish a relationship between the 3DSP printing parameters and the ultimate mechanical properties of the consolidated parts, many studies have been recently done [27,30,33,34,36,37,42,43]. The effect of printing orientation and recoating speed on the mechanical properties of the samples have been evaluated by Coniglio et al. [33]. Mitra et al. [34] also verified the influence of the 3DSP processing parameters on their respective mechanical and mass transport properties. Recent
Conclusions
A study of the ExOne sand 3D printing process, commonly used in the foundry industry, has been carried out. It is based on a new mechanical test strategy to evaluate the impact of the parameters of the 3D sand printing process. It has been found that the experimental device developed in this study considerably increases the reproducibility of the results by improving the boundary conditions during the loading of the printed specimens. The mechanical characteristics in compression, such as the
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
We are grateful to Jérémie Bourgeois for their assistance in 3D printing of sand specimens and Fabrice Guittonneau for performing the SEM micrograph acquisitions. We thank Regis Kubler and Laurent Barrallier for their suggestions and the exchange of ideas on the general subject of mechanical characterisation and microstructural analysis. Jonathan kenny is thanked for his review and comments regarding the scientific content of this work.
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2022, MaterialiaCitation Excerpt :Compared to conventional sand mould preparation, 3DSP provides much greater design freedom plus improved dimensional control, hence it is proving especially useful for low-volume production of complex shaped parts [3,4]. Much of the work on castings production via 3DSP has been focused on design capability [5,6] machine and process variables [7,8], binders [3,9], casting integrity and surface finish [3,4,10], economics [3,4,11], integration into traditional foundry operations [12,13] and sustainability [14]. There is relatively little work on the microstructures of castings produced in 3DSP moulds and this has concentrated on Al-Si alloys [15,16].