## 1 Introduction
### Topology Optimization Workflow  
The Design phase, including Topology Optimization, can be inserted in a higher general workflow of Design for Additive Manufacturing [16], as is visible in Figure 1. The input of this phase is Product Planning includes several activities such as data collection, feasibility studies, preliminary analyses, the definition of projects objectives and constraints. Subsequently, the Design phase can start, with the aim to maximize product performance and thus to optimize its design considering the AM process. Afterward, Industrialization is required, including build preparation to create the job, and eventual process simulation. Finally, the production can start, with product printing and related post-processing and control steps required.  
The Design phase, as the key task of Design for Additive Manufacturing (DfAM), can be based on Topology Optimization approaches to create a lightweight and functional design. In order to perform a topology optimization of a product by using available design tools, the sequence of tasks that are included in the workflow is now described. The main steps are Geometry preparation, Optimization setting, and Results and Post-processing.  
* TO1--Geometry preparation.  
The first phase aims to create the 3D geometries to be used to compute a TO by means of CAD tools. The first step can be the direct model import of the original non-optimized part or the retrieve of elements required as boundary conditions, related to the assembly where the part has to fit and work. Subsequently, the Design Space, or rather the volume set for shape computation, must be created. According to geometrical constraints, it must be as large as possible, so that the material distribution can be calculated with maximum freedom. A Non-Design Space is required as well to define the forbidden volumes for shape computation, since they have to be kept for functional reasons. Moreover, a key step is the material definition for further model simulation.  
* TO2--Optimization setting.  
The aforesaid 3D geometries need to be discretized by creating a finite element model. The first step is mesh generation, selecting the type and size of elements and introducing the required refinements. Afterwards, in order to simulate product physical behavior, proper sets of loads and restraints need to be created and applied to the model. Finally, the optimization can be set up, including at least one target and one constraint. Moreover, implemented manufacturing constraints and geometrical constraints can be included, as well as the opportunity to interact with algorithm solving by additional  
Figure 1: Topology optimization workflow.  
settings made available by user interfaces. Solving parameters may also be specified for the iterative computation.
* TO3--Results and Post-processing.  
Once a result has been obtained, in general, the possibility to visualize it and analyze it should be granted. A basic finite element analysis of the computed model can be provided, or a geometry generation can be preliminarily required. This output can be automatically created by the design tools; conversely, in the worst case, no data about the computed result are provided. In this latter instance, firstly a manual geometry interpretation by CAD modelling is necessary and finally, a finite element analysis of the new model can be performed. A key point is the possibility to manipulate the geometry for results displaying, design modification, or further simulations.