# Topology Optimisation in Structural Steel Design for Additive Manufacturing
## 8 Future Trends
Conclusions drawn from structural steel TO suggest that a higher optimisation grade and further proofs of safe applicability of additively manufactured connections are the future paths for achieving economic viability, compared with labour-intensive traditional manufacturing [355]. Focusing on the AM process, [PERSON] and [PERSON] [81] concluded that future directions in three-dimensional printing for architectural purposes include large-scale printing, Artificial Intelligence (AI) embedment into the design process, and computerized assembly [81]. In addition, [PERSON] et al. [595] mentioned the accounting for metal AM residual stresses and the costly post-machining as issues yet to be solved, as [PERSON] et al. [594] stressed out material performance assurance and fabrication speed and resolution as future research lines. Future research on AM methods is deemed to comprise solutions for lightweight cellular materials design [594] or the validation for AM purposes of several innovative TO approaches [595]. Another perspective on future trends can be attained from analysing current funded projects and recent patents on a subject. Searching within the EU projects database, one can find two projects concerned with TO. An already finished project studied _\"Optimization Techniques for MIMO Radar Antenna Systems\"_[596] and therefore, is not related to this review scope. On the other hand, the project _\"Innovative Re-Design and Validation of Complex Airframe Structural Components Formed by Additive Manufacturing for Weight and Cost Reduction\"_ has been funded since 2017 until the current year under the framework of _\"Design Guide Lines and Simulation Methods for Additive Manufactured Titanium Components\"_ and deployed significant publications [127; 178; 597; 598]. While the research has been conducted with titanium as the primary material, the innovative approaches are applied in any engineering field where weight reduction is a major objective. Concerning recent Topology Optimisation patents with the world, Europe, or US coverage, software developers have registered several computational methods. Those include Livermore Software general design methods EP2251805A2 [599] and US8126684 [600], the numerical derivates method US0160078161 [601], and enhanced global design variables method to account for impact events US0170255724 [602]. In addition, Dassault Systemes' method for designing a mechanical part with TO EP3502931A1 [603], US20190197210A1 [604], EP3647973A1 [605], and JP2020071887A [606], as well as autodesk TO for subtractive manufacturing techniques US 2018/0349531 [607] and Altair's Failsafe TO method US10354024 B2 [608]. Other recently patent-protected design methods include patents US20160140269 [609], US8335668 [610], and WO202021553A1 with a material-field reduction series expansion [611], EP3285189A1 for flexible hinges [612], EP3292657A1 and US0180139130 for the multi-layer network TO [613; 614], US0170161405 employing reduced length boundaries methods [615], US0200134918 for cellular structures [616], and US010613496 for Additive Manufacturing [617]. Unlike what has been depicted for published research, patents show a significantly growing impetus for practical methods, especially in automotive, composite materials manufacturing, and aerospace industries. In fact, while the 2010 to 2015 period has some of the most significant TO industrial patents in Caterpillar's US0100274537 stress-based TO method [618] and US0140156229 fatigue-based TO method [619], the last 5 years brought several and significant advances, such as Toyota's methods for TO with a member ship variable WO2019152596A1 [620] and US0090326138 with shape transformation [621].