The ever-expanding field of topology optimization (TO) includes the recent development of multi-material topology optimization (MMTO). In this work, the shortcomings of MMTO concerning concept complexity and impracticality with design interpretation are discussed. The current field is explored, for emerging manufacturing constraints which aim to reduce design complexity and promote practical usage of MMTO. The importance of the draw-direction constraint is established, with a methodology for their implementation into MMTO presented.
The proposed MMTO approach is density-based and relies on solid isotropic material with penalization (SIMP) for material interpolation, and the method of moving asymptotes (MMA) for optimization. The aforementioned draw-direction constraints are implemented into MMTO with a design variable projection technique. Three different types of draw-direction constraints are created, with varying levels of complexity for a set of options for balancing structural performance and design complexity. These constraints are demonstrated across a series of academic models along with a discussion of their comparative performance benefits and drawbacks. In closing, the application of these constraints to large-scale industry problems is evaluated, especially about the real-world challenge of material interfaces and component consolidation.