Additive manufacturing oriented topology optimization of structures with self-supported enclosed voids

It is challenging to remove the supports in an enclosed void of an additively manufactured structure, while it is much easier in open regions. This paper presents a novel approach to control the minimal overhang angle only in enclosed voids in order to improve the manufacturability of AM structures with as little performance loss as possible. Firstly, a nonlinear virtual temperature method (N-VTM) is proposed to identify the enclosed voids. In the N-VTM method, void areas are assumed to be filled with a temperature-dependent heating material with high heat conductivity while the solid parts have low heat conductivity. Due to a nonlinear heat source term, the maximum temperature is controlled to a prescribed value, making the temperature in enclosed voids uniform over the whole structures. Hence, the enclosed voids can be easily identified without a careful selection of parameters. Then, the gradient of the filtered density field is applied to evaluate the overhang angle of the interface. Finally, a multiple filtering/projection process is developed to identify the overhang interface of enclosed voids, and then a logarithmic function-based constraint is developed to control overhang angle in enclosed voids by restricting the area of overhang interface of enclosed voids. Enhanced by the robust formulation, a topology optimization method for the design of structures with self-supported enclosed voids is then established. Several numerical examples are used to illustrate the effectiveness of the proposed method.