# Review and New Aspects in Combining Multipoint Moulding and Additive Manufacturing
## 3 Possible Additive Manufacturing Methods
### Additive Manufacturing on Curved Surfaces
#### 4.2.2 Curved Slicing Methods  
In addition to the today most commonly used methods using flat slices, the algorithms for curved layers are developed and tested in [87, 88, 89, 90, 91, 92]. The method investigated there is called curved layer fused deposition modelling (CLFDM), where flat layers are replaced by curved layers that are adapted to the component contour. As shown in Figure 16, the curved model (a) is classically sliced in flat layers (b) resulting in a visible staircase effect. In order to take advantage of these curved layers it is necessary for the components to be manufactured along curved extrusion paths. In this case, a significant improvement in surface quality can be achieved, as illustrated in Figure 16c. Moreover, the components, manufactured by curved layer fused deposition modelling, show increased strength. If the number of layers can be additionally reduced due to the curved production layer, the building speed increases compared to the classic flat layer variant. [PERSON] and [PERSON] [88] examine the influence of the building direction on the mechanical properties and find that the components where the extrusion strands oriented in the load direction can sustain  
Figure 15: Comparison of the staircase effect between standard slicing and the TruSurf algorithm (based on the work in [52]). approximately 500% of the load compared to strands lying transversely to them. [PERSON] and [PERSON] [89] extend the process by combining the classic flat layer structure with curved layer fused deposition modelling for the surface strands to achieve a further advantage in construction speed. Such a combined procedure is also examined by [PERSON] and [PERSON] [93]. They show that the combination of the two layering techniques lead to an improvement in surface quality and at the same time also improve the mechanical properties, although a load-compatible extrusion path is only present in the outer layers. [PERSON] et al. [87], on the other hand, show another application for curved layer fused deposition modelling in electrical engineering. Here, the curved layer fused deposition modelling makes it possible to integrate conductor tracks directly into curved components and thus to create parts without circuit boards and connecting wires. [PERSON] et al. [94] use a similar process to go further and produce the entire component from only one continuous extrusion strand. In the subsequent investigation of the mechanical characteristics, a clear improvement compared to processes using flat slices can be attributed to a better load distribution in the part. On the downside, the fracture behaviour changes from ductile to brittle fracture without warning of failure. Such an improvement of the mechanical characteristics is also demonstrated by [PERSON] et al. [95] for the \"Concrete Printing\" process [57] if curved layer fused deposition modelling is used and the extrusion paths are generated according to the load paths in concrete parts. Compared to the methods with flat layers the calculation of the extrusion paths for the curved layer fused deposition modelling presents a greater challenge, as the ideal curvature of the slices for the component surface must be determined. In addition to the algorithms already mentioned, [PERSON] et al. [96], [PERSON] et al. [97] and [PERSON] et al. [98] have each conducted their own investigations on the ideal layer generation and present corresponding methods and algorithms. [PERSON] and [PERSON] [99] go further and reduce the component to a skeletal model with material only in the main load directions. Therefore, a significant material saving can be achieved compared to a full model. In terms of using this method for moulding parts, it would be necessary to adapt the process for getting a closed surface at this side of the part where the moulding should take place. Another challenge is the production of components in three-dimensional paths. [PERSON] et al. [100] are developing a process that uses the additional axes available in conventional CNC machining centres.