# Conformal 3D Material Extrusion Additive Manufacturing for Large Moulds
## 2 Materials and Method
### Customised Desktop Hybrid Manufacturing Machine  
A scaled-size prototype of a hybrid machine has been constructed to validate the hybrid manufacturing approach suggested in the previous paragraph and assess its benefits and drawbacks. A straightforward case study involving the creation of a small mould has been considered. A 3 Drag FFF cartesian machine has been chosen to validate the proposed methodology [33]. The FFF machine has a 200 \(\times\) 200 \(\times\) 200 mm building volume, a nominal resolution of 0.015 mm in the X and Y axes and 0.039 mm in Z, and a heated bed. However, the latter characteristic is not vital for this research. Thus, the heated bed has been disconnected; indeed, large-scale hybrid manufacturing machines for mould fabrication do not require a heated bed. The choice fell on this machine because kits are available online to convert it from a 3D printer to a CNC machine. The FFF machine has been modified to host a low-power drill/grinder with a power of 130 W, a rotation speed of 10,000-33,000 rpm and a flexible shaft. Thus, a bracket has been designed, printed with PLA material, and fixed to the X rail of the machine near the extrusion head (Figure 6). The bracket is assembled with a butterfly screw anchor to easily adjust the height of the spindle during the AM process to avoid dangerous collisions because of the considerable exposed length of the spindle. Figure 6: Low-power tool for material removal (**a**) spindle with the flexible shaft; (**b**) installation on the X gantry of the FFF machine. The butterfly screw permits an easy setting of the spindle height. The position of the CNC tool should comply with requirements such as:  
* the spindle should not disturb the operations of the nozzle during 3D printing;
* univocal (X, Y) positioning of the tool during the entire manufacturing cycle;
* it should be removable if necessary;
* it should be as close as possible to the extrusion head not to waste a portion of the working area. Moreover, the end-stops of the hybrid manufacturing machine have been modified to optimise the motion of the tools. Initially, the AM machine recognised the position closest to the bed as the extruder Z home position, which can cause problems. Indeed, when the hot end moves to the Z home, it could hit the core material or the structure that was previously milled and not removed from the bed. The position of the end stop of the Z axis has been changed by fixing it at the top; this framework design prevents possible conflicts between the extruder head and walls in case of concave shapes. A support was designed to host it and allow it to be fixed to the Z gantry. Accordingly, the machine firmware has been updated with the \"MarlinKimbra\" version because it better meets the project's needs. The following section of the paper describes a practical application to validate the methodology using a case study dealing with manufacturing two small parts to proxy the actual fabrication of a mould and the lamination of CF efficiently. First, a simple sandwich structure made of two 3D-printed external shells (one at the bottom and one at the top) and a milled core of expanded PVC has been manufactured according to the scheme shown in Figure 1b. The external shells were produced using a traditional LM approach to verify the functionality of the hybrid desktop machine. PLA has been chosen for the external shells because it does not necessarily require a heated surface to stick on the printing bed, while an expanded PVC board has been selected for the structure's core. The second test is used to validate the spatial material deposition methodology described in Section 2.1. A down-scaled mould structure, similar to what is represented in Figure 1c, has been manufactured. PLA mimics the CFRP deposition along 3D conformal paths over the PVC milled board. Between these two materials, the deposition of some layers of PolyVinyl Alcohol (PVA), a commercial filament soluble in water, aims to simulate the release agent spread manually over the moulds.