# Design for Additive Manufacturing and for Machining in the Automotive Field
## 1 Introduction  
Additive Manufacturing (AM) offers promising benefits for the production of lightweight automotive components of complex geometry, such as those derived from the process of topology optimization (TO) [1; 2; 3]. TO is a mathematical approach to redesign material distribution within a given design space (DS) in order to optimize a defined property or performance of the system under the effect of a given set of loads, boundary conditions and constraints. Unlike shape optimization and sizing optimization, the new shape attained through TO can fill the DS freely, without conforming to predefined configurations [4]. Therefore, results given by TO are usually complex geometries, which can hardly be realized through conventional manufacturing methods [5]. On the contrary, TO fits perfectly to additive manufacturing (AM) because this technology has very few design constraints, so that it is possible to follow the output geometry independently of its complexity [6]. After TO, the industrialization of the redesigned geometry requires its orientation to be optimized within the building volume, which affects distortion and surface finishing [7; 8]. For the former issue, orientation should be chosen in such a way that the cross-sectional area remains as uniform as possible along with the growth (z) direction, because a sudden change is expected to cause part distortion as a consequence of the high energy that is driven into the component without appropriate heat exchange. For the latter aspect, surface roughness is related to part orientation for two main reasons: the so-called staircase error, which derives from the layer-wise build-up strategy and is deeply influenced by the orientation of surfaces, and the poor surface quality left when supports are removed. If required, in the framework of industrialization, supports are preferentially located on the part surfaces to be machined after manufacturing because machining will remove the contact points. Orientation also impacts the overall cost since it governs the part height and, therefore, the building time [9]. Design for Additive Manufacturing (DfAM) is the practice of designing and optimizing a product together with its additive production system to reduce development time and cost and increase performance, quality, and profitability [10; 11]. The process involves, as an example, the concurrent design and reciprocal optimization of the part geometry and of its orientation within the machine-building volume so that self-supporting areas are maximized [12]. The same holistic approach also includes considerations for surface finish and distortion. Among the tools currently available for DfAM, software packages for part industrialization usually include specific tools to select the most convenient locations for supports and to optimize the part orientation [13; 14]. Process simulation can be helpful in predicting the output of a given orientation and support strategy. However, it is worth noting that dedicated process simulation programs are still relatively rare and often under development as a consequence of the very recent establishment of laser-based powder bed fusion (LPBF) as a leading manufacturing technology [15]. Even if LPBF is usually considered as a net shape production method, post-processing steps such as thermal treatment and surface finishing are often needed. As a matter of fact, LPBF implies out-of-equilibrium thermal conditions, extremely fast cooling rates and sharp thermal gradients, which are expected to engender strong thermal residual stresses in as-built parts. Hence, a thermal treatment is usually performed to relieve thermal stresses [16; 17]. The roughness of LPBF parts is typically high, with Ra values that are in the 6 to 9 \(\upmu\)m range for vertical surfaces and even higher for down-facing surfaces [18].