# Review and New Aspects in Combining Multipoint Moulding and Additive Manufacturing
## 2 Vacuum Assisted Multipoint Moulding
### Restrictions and Solutions  
Overall, it was shown that this technology has a broad field of application in various forming processes. Particularly in single-part and small-batch production, the time-consuming and expensive production of moulds can be dispensed. On the other hand, there are still various restrictions. [PERSON] et al. [23] show that size and shape of the pins as well as the interpolation layer used result in a certain resolution of the system. This means that, depending on these parameters, the structure manufactured on the plant must have a minimum size. Another limitation results from the maximum deformability of the interpolation layer, therefore two adjacent pins must not exceed a certain maximum height difference in order not to damage the interpolation layer. This in turn means that sharp-edged transitions cannot be represented. Figure 5 shows a schematic part made of carbon fibre reinforced plastics including a detail which is not producible with vacuum-assisted multipoint moulding. Real components that correspond to the schematic in Figure 5 could be, for example, doors of cars with a door handle recess. The vacuum-assisted multipoint mould can be configured for the slightly curved section of the part, but not the buckle in the centre. On one hand, this buckle may be too small for representation with the pins of vacuum assisted multipoint mould. On the other hand, there are sharp edges which cannot be configured with the silicone made interpolation layer without damaging the interpolation layer. Naturally, other components are also a possibility, for example, with an additional negative form element. To solve this problem, [PERSON] et al. [26] propose the application of attachments to the interpolation layer. These attachments are to be used in areas representing geometries that  
Figure 4: 3D scans of bowl shape created with a silicon rubber interpolation layer (40 Shore-A) with varying thickness (**(a)** 5 mm, **(b)** 10 mm, **(c)** 15 mm and **(d)** 20 mm) at a vacuum of 100 hPa [23]. Figure 5: Schematic of a CFRP-part including a detail not producible with VAMM in the central part. cannot be mapped on the vacuum-assisted multipoint mould. As shown in Figure 6, this concept consists of the classical vacuum-assisted multipoint mould approach with the pins mounted in a vacuum chamber and a flexible interpolation layer at the top. On top of the interpolation layer an additive manufactured attachment is mounted to build the detail which cannot be represented by the vacuum assisted multipoint mould. The fixing of the externally manufactured attachments on the interpolation layer is identified as a problem. Three different solutions are presented, two of them are types of vacuum mounting and the third is a needle mounting system. The combination of the vacuum-assisted multipoint moulding and the additive manufactured attachments has the opportunity to combine a fast moulding process with the possibility for smaller details without producing a mould. Building the whole part with additive manufacturing processes would consume a lot of time, although the parts are thin-walled. On the other hand, the construction and milling of a mould needs even more time, even if the moulding process itself is fast. When combining the vacuum assisted multipoint moulding with additive manufactured attachments on one side the additive manufactured parts are relatively small and thus can be manufactured in a short period of time. On the other side, when using the vacuum-assisted multipoint mould there is no mould-milling necessary which significantly reduces the time required. The positioning problem of these attachments on the vacuum assisted multipoint mould is not completely solved. If a manual positioning is carried out, deviations in dimensional accuracy can be expected. In addition, trained employees are needed for manual steps, which generally reduce the efficiency of the technology. A further aspect is the need to pick up the surface in order to be able to produce precisely matching attachments.