Abstract
The design of optimal structures and the planning of (additive manufacturing) fabrication sequences have been considered typically as two separate tasks that are performed consecutively. In the light of recent advances in robot-assisted (wire-arc) additive manufacturing which enable addition of material along curved surfaces, we present a novel topology optimization formulation which concurrently optimizes the structure and the fabrication sequence. For this, two sets of design variables, i.e., a density field for defining the structural layout, and a time field which determines the fabrication process order, are simultaneously optimized. These two fields allow to generate a sequence of intermediate structures, upon which manufacturing constraints (e.g., fabrication continuity and speed) are imposed. The proposed space-time formulation is general, and is demonstrated on three fabrication settings, considering self-weight of the intermediate structures, process-dependent critical loads, and time-dependent material properties.
Highlights
Recent advances in additive manufacturing (AM, known as 3D printing) enable the fabrication of structures with unprecedented geometric complexity
We present a general formulation where the objective function could take into account the structural properties of both intermediate structures as well as the complete structure
We have presented a general formulation for simultaneous design of the structural layout and the manufacturing sequence, referred to as space-time topology optimization
Summary
Recent advances in additive manufacturing (AM, known as 3D printing) enable the fabrication of structures with unprecedented geometric complexity. A number of aspects, including self-weight, material curing and solidification, thermal dissipation and distortion, are influenced by the fabrication sequence These aspects in turn affect the (mechanical) performance of the structure at both the intermediate and final stages. We impose general constraints on intermediate structures, regarding fabrication continuity and process speed This general formulation is demonstrated by integrating a few simplified yet meaningful aspects that are associated with the fabrication sequence, including self-weight of the intermediate structures, process-dependent loads, and timedependent mechanical properties (e.g., in a curing process). Allaite et al (2017a, b) proposed a novel mechanical constraint functional, which mimics the layer by layer construction process featured by additive manufacturing technologies This constraint aggregates the selfweights of all the intermediate structures.
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