# Topology and Parametric Optimization-Based Design Processes for Lightweight Structures
## 3 The Experimental Design Process  
As already mentioned in Section 1, the aim of the authors was to develop different design processes based on possible combinations of topology and size/shape parametric optimization. Thus, ten different design processes were created and executed in an Intel Core I7-7820 HQ computer with 32 GB RAM. Three case studies: A Hollow Plate, an L-Bracket, and an MBB-Beam were used to test the design processes. Hence, 30 simulations were conducted in total. Their results were compared with respect to mass, optimization time, and stress. An overview of the implemented design processes is presented in Table 1.  
In addition, the authors clustered the design processes to those that can lead to designs that either can be mainly produced by AM (3D printing) or both by AM and CMP. An illustration of this categorization is depicted in Figure 3. Each of these processes consists of a maximum of four optimization levels. Furthermore, the main processes were classified, based on their first optimization level, in three main design workflows; TO, PO, and simultaneous PO and TO. The goal of these workflows was the mass reduction of the structures with respect to their yield strength. The first level optimization can be followed either by a no redesign/redesign or TO procedure at the second level and possibly, with a new PO round at third and fourth level for a further mass reduction. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Design** & **Design Process** & **Description** & **Production Method** \\ \hline \multirow{6}{*}{Topology Optimization} & (1) TO\_NR & topology optimization with no & AM \\  & & redesign & AM + CMP \\ \cline{2-4}  & (2) TO\_R & topology optimization with & AM + CMP \\  & (3) TO\_R\_PO & redesign and parametric shape & AM + CMP \\  & & optimization & AM + CMP \\ \hline \multirow{6}{*}{Parametric Optimization} & (4) PO & parametric size/shape & AM + CMP \\  & & optimization & AM + CMP \\ \cline{2-4}  & (5) PO\_TO\_NR & parametric size/shape, and & \\  & (5) PO\_TO\_NR & topology optimization with no & AM \\  & & redesign & AM + CMP \\ \cline{2-4}  & (6) PO\_TO\_R & parametric size/shape, and & \\  & (6) PO\_TO\_R & topology optimization with & AM + CMP \\  & & redesign & AM + CMP \\ \cline{2-4}  & (7) PO\_TO\_R\_PO & parametric size/shape, topology & \\  & (7) PO\_TO\_R\_PO & optimization with redesign, and & AM + CMP \\  & & parametric shape optimization & \\ \hline \multirow{6}{*}{Simultaneous Parametric and Topology Optimization} & (8) PO + TO\_NR & simultaneous parametric & \\  & & size/shape and topology & AM \\  & & optimization with no redesign & \\ \cline{2-4}  & (9) PO + TO\_R & simultaneous parametric & \\ \cline{2-4}  & (10) PO + TO\_R\_PO &
\begin{tabular}{c} simultaneously parametric \\ size/shape and topology \\ optimization with redesign, and \\ parametric shape optimization \\ \end{tabular} & AM + CMP \\ \hline \multicolumn{4}{c}{TO: Topology Optimization; PO: Parametric Optimization; R: Redesign; NR: No Redesign; AM: Additive Manufacturing; CMP: Conventional Manufacturing Processes.} \\ \end{tabular}
\end{table} 
Table 1: The ten implemented design processes, their name, description, and production method. The most implemented design process is the topology optimization with redesign and parametric shape optimization (TO_R_PO), process (3). A representative example of this design process in the literature is the topology optimization of the leading-edge rib of an aribus A380 [23]. The general idea of the presented methodology in this example is that first, the initial design is topologically optimized. Then, it was redesigned at the second level, and finally, it was used as input in a size/shape parametric optimization. This last step contributed to TO with an additional mass reduction of the structure. Furthermore, the redesign, together with the PO, helped in overcoming possible stress concentrations at the optimized topology design and made its manufacturing feasible by the conventional processes.