# On the Impact of Additive Manufacturing Processes Complexity on Modelling
## 4 Discussion  
### Classification of Processes  
As mentioned, the part size and the temperature could be used as criteria for process selection. The first one separates the mainly cement-based AM from the others, where the temperature is used as a classifier of the rest of them. As a matter of fact, in a draft quantified way, they seem to lie along a curve that resembles the equation _Temperature = a/Part size_.  
Therefore, as summarized in Figure 9, it may be observed that metal- and cement-based AM process groups are at the edges of the spectrum of the aforementioned parameters: Metal-based AM presents the highest temperature, very high complexity, and fine part size; the opposite is true for cement-based AM, as it presents low temperature and motion complexity and the largest part sizes. Subsequently, these two processes are ideal for the investigation of part quality focusing on the effect of the movement of the head. More specifically, in metal-based AM, the path component defines the gradients of the thermal field over time, which leads to the development of thermal stresses and deformations [17; 22]. Moreover, metal-based AM processes feature the highest temperatures and some of the lowest part sizes. In contrast, in cement-based AM, the speed over time directly affects the dimensions and consistency of the deposited path because the process mechanism involves material flow from the head onto the machine platform [21]. The relatively large path dimensions compared with those of the layer further increase this effect. In addition, the process temperatures in cement-based AM are the lowest compared with those of all AM process groups, whereas the final part sizes are the largest. Finally, both the metal- and cement-based AM process groups attract ever-increasing industrial interest, while simultaneously, in both cases, there is a need for improvement of technical issues regarding part quality.  
Furthermore, the (process) complexity, that is also related to modelling, can be introduced as an extra scale in this diagram, a third axis, in order to accommodate the fact that there are many more process parameters and many more performance indicators to take into account during modelling, as well as their mutual relationship complexity also varying. Once again, it seems that the metal- and cement-based AM process groups require completely different treatment (and effort) towards their performance prediction.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Process** & **Material** & **PP–KPI Entropy (bit)** & \multicolumn{2}{c}{**Process-Mechanism Spatial Complexity (bit)**} & \multicolumn{1}{c}{**Total Entropy (bit)**} \\ \hline SLM & Steel & 13 & 8 & 21 \\ FDM & PLA & 7 & 5 & 12 \\ SLA & Resin & 4 & 0 & 8 \\ Cement-based AM & Concrete & 7 & 0 & 5 \\ \hline \hline \end{tabular}
\end{table}
Table 6: Total complexity.  
The aforementioned facts make these two process groups ideal for the investigation of the effect of the head movement on part quality. Hence, the investigation of the effect of head path planning on quality has been performed by modeling metal-based AM [22]; meanwhile, the effect of speed on quality has been investigated by modeling cement-based AM [21].