# Development and Assessment of a 4D Printing Technique for Space Applications
## 2 Materials and Methods
### 3D and 4D Printing  
Three-dimensional printing is a relatively new manufacturing method compared with other manufacturing techniques. In 3D printing material is deposited in layers and lines; multiple of these lines are deposited next to each other, forming layers, which are deposited on top of each other forming the final part geometry. In this work, the primary focus will be on the polymer 3D printing technique known as fused filament fabrication (FFF), also referred to as FDM. FFF is categorized as a material extrusion-based 3D printing method. In FFF, a thermoplastic polymer in filament form is extruded through a nozzle. The filament undergoes a melting process within the nozzle and is then deposited onto a build platform, typically in linear patterns, while in its molten state. The polymer subsequently solidifies, capitalizing on the thermoreversible networks inherent in thermoplastic materials. The nozzle is an integral component of the 3D printer's print head, which maneuvers along three axes, enabling the production of three-dimensional objects. After the material is deposited onto the build platform, it undergoes cooling. When the new material is deposited adjacent to or above the previously deposited layer or line, the thermal energy from the freshly deposited material facilitates (partial) fusion with the existing material [22]. In the context of this study, 3D printing serves as the pivotal method for fabricating the hinges crucial to our investigation. The hinges, designed as a simple rectangular geometry, were initially conceived as a baseline for subsequent explorations into more suitable hinge shapes. Surprisingly, this basic geometry exhibited an exceptional performance in our preliminary tests and, as a result, became the focus of our experimentation. The selected hinge geometry, measuring 90 mm \(\times\) 24 mm \(\times\) 0.4 mm, was deliberately crafted to be thin and long This specific design, featuring a slender structure, was proven to be advantageous for the intended application as a self-opening hinge. The inherent high deformability of this geometry aligned with the requirements of the intended use case. The unfolded and folded hinge are displayed in Figure 1.  
When working with 3D printers, there are three steps in creating the final 3D printed part. 1. **CAD modelling:** The hinge geometry was initially modelled using computer-aided design (CAD) software ([[https://www.solidworks.com](https://www.solidworks.com)]([https://www.solidworks.com](https://www.solidworks.com)), (accessed on 14 November 2023)). During this phase, careful consideration is given to the orientation in which the part will be printed to avoid challenges such as overhangs or difficult-to-print sections. 2. **Slicing:** Once the CAD model was finalized, it was exported to a.stl file, creating a meshed version of the part. This file was then loaded into a slicing program, in this case, Cura. In the slicer, the printing process was planned, and various process parameters were fine-tuned based on the specific part geometry. Common parameters included print speed, print temperature, and line width, which significantly influenced the final printing outcome. The slicing software generated a G-code file containing the instructions for the 3D printer. 3. **3D printing on Orion's A150:** The 3D printer employed in this study was developed by Orion Additive Manufacturing GmbH (Orion). Orion's printer surpasses traditional FFF capabilities with its  
Figure 1: The unfolded hinge before programming on the left and the folded programmed hinge on the right. innovative system specifically designed for engineering polymers like PEEK. Notably, it achieves nearly 100% density and isotropic strength values that are comparable or even better than those of injection-moulded parts [15]. The key to this success lies in Orion's thermal radiation heating (TRH) system, maintaining a warm printing chamber. Active heating during printing ensures the effective fusion of layers, minimizing air pockets.