# Conformal 3D Material Extrusion Additive Manufacturing for Large Moulds
## 2 Materials and Method
Moreover, it is essential to pay attention to the frame of reference of the coordinates in the G-code instructions when utilising a single G-code to control several tools that are not in the exact location of the machine. Finding the relative distance between the subtractive tool head and the extruder requires special consideration (Figure 3). The following instructions are used to add this data to the G-code:  
_G0 Xnnn Ynnn_  
_G92 X0 Y0 Znnn_  
where \(nnn\) is the distance between the tools' positions in mms along the three axes. Figure 2: Graphical representation of the hybrid manufacturing framework described in this research. A typical structure/mould manufactured using the proposed methodology consists of an assembly given by a core and one or more external coatings, as seen in Figure 1. Using the composite structure shown in Figure 1a as a reference and according to the flowchart shown in Figure 2, the user will first create the digital model of the internal core of foam material (e.g., expanded PVC) with a curved upper surface skin body. The next stage involves the digital model of an external shell of a few millimetres, which is necessary to produce the external coating layers using AM techniques along novel conformal paths. The separate digital bodies are then correctly positioned in an assembly file and must be exported as separate files from CAD software. By doing this, the separate models may be loaded into CAM software with the appropriate relative distances and frames of reference. Traditional FFF uses a Layered Manufacturing (LM) method that reflects a noticeable stair-step effect (Figure 4a). This phenomenon might be especially problematic when making moulds for high-performance applications such as aerospace, marine, or automotive industries, where highly smooth external surfaces are required for aerodynamic/fluid-dynamic/structural purposes. A conformal 3D spatial deposition of fused material can represent a crucial strategy to enhance the manufacturing of the external coating of moulds. Instead of planar paths, the filaments are deposited along curved (basically non-horizontal) routes, which suggests an entirely new building strategy for FFF (Figure 4b). Curvilinear (non-horizontal) material deposition has been discussed in earlier scientific works about AM [26; 27]. However, to the best of the authors' knowledge, modifying a milling 3-axis G-code instruction for usage with an AM machine has not been adequately addressed in the scientific community. In particular, the proposed methodology uses as input a G-code file obtained with a modified \"CncMasters-Metric\" post-processor [28] of CAM software and uses a virtual tool of the same diameter as the nozzle of the hybrid machine that mimics a finishing process. The \"CncMasters-Metric\" post-processor for a 3-axis machine has been chosen for the project's aim because the G-code layout is very similar to the AM layout. The 3D CAD  
Figure 4: Schematic representation of material deposition of (**a**) traditional FFF layered manufacturing; (**b**) 3D curved layer supported by CNC milled mould. Figure 3: Schematic representation showing the relative position of both tools in the machine. models are converted through CAM software into G-code instructions using the modified post-processor according to the user's needs. The authors concentrated on integrating conformal 3D curved paths for AM in addition to eliminating the support material in conventional Fused Filament Fabrication (FFF) procedures. Indeed, a traditional FFF machine only moves the \(Z\) axis when there is a layer change and moves the \(X\) and \(Y\) axes simultaneously. This approach is critical when good strengths are required because high anisotropy affects the final object [29]. Therefore, this research aims to build a 3-axis hybrid machine to cope with the drawbacks of the typical 2.5D material deposition, such as the high stair-step effect, the need for support material, high surface roughness, and strong anisotropy.