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- Quality in metal AM
In this chapter quality aspects related to Design for Additive Manufacturing are discussed. A short summary with external links is given of the full document, which can be downloaded HERE.
Keywords: Quality of STL files, Build profile, Design guidelines
- What determines quality of a design?
- Quality of the STL file and Build Profile
- Design Guidelines
- Topology optimization
- Support structures, part orientation and build strategy
- Further reading
1. What determines quality of a design?
For additive manufacturing a design includes four aspects:
- Part geometry
- Build orientation
- Support structure
- Build profile
Specific part requirements specify the boundary conditions to which a part must comply in order to qualify for the function of the part. A design must consider the various elements of the value-chain – and their interaction - in order to meet the part requirements. Finally, a design needs to consider the interaction between the other parts in the system in which it acts.
2. Quality of the STL file and Build Profile
The STL file format is the most commonly used file to represent the geometry of the part to be produced by additive manufacturing, but does not contain properties for specific applications. These properties, i.e. multi-material, graded structures and repetitive unit cells, are incorporated in the AMF (Additive Manufacturing File) format.
STL file requirements, CAD-STL conversion are key topics to consider with relevance to quality.
3. Design Guidelines
In recent years, several works have been carried out concerning the classical design for manufacturing approach for additive manufacturing (Ponche et al, 2012. Gupta et al, 1997). In particular, general build guidelines have been established by Filippi et al (2007) and Teitelbaum (2009). This work has primarily focused on design-for-manufacturability (DfM); that is, what types of geometric components are suitable for inclusion in a design for AM while complying with process specific manufacturing constraints.
Aside from macroscopic considerations, a significant amount of work by Rosen (2007) has focused on the implementation and design guidelines for the inclusion of meso-structures (or internal lattice-type, cellular structures) in AM builds. Building on previous work, Thomas (2009) set out to develop a concise and self-contained set of design rules for SLM.
ISO/ASTM DIS 52910: Guide for Design for Additive Manufacturing was developed for standardisation of design guidelines.
3.1. Topology optimization
In parallel with these design-for-manufacture studies, software for topological optimisation has become increasingly commercially available and user-friendly (Chahine 2010). The essence of topology optimisation is that it identifies areas of a domain that have inefficient levels of stress and then removes these regions in order to increase the overall stress-bearing efficiency of the component, thus resulting in an optimal material distribution.
3.2. Support structures, part orientation and build strategy
Main Support Structure aspects are: CAD supports, optimization of support's geometry, optimization of part surface, optimization at platform and optimization in between of platform and part.
Part orientationand build strategy aspects are important surface, layer thickness and lightweight structures (Thomas 2009).