Real-Time Nonlinear Tracking Control of Photopolymerization for Additive Manufacturing

In the context of additive manufacturing (AM) and 3D Printing, vat photopolymerization is an established technique in which photopolymer is selectively solidified to form a near-net-shape part. Photopolymerization-based AM is increasingly being adopted by the high-tech industry, but the technology still faces several challenges in terms of consistency in product quality, understanding of the UV curing process, in-situ process monitoring, and real-time closed-loop control. This paper aims to demonstrate the potential of model-based control of the UV curing process. The curing process is modelled and anticipatively controlled with an optimal control law for nonlinear systems, derived via a sequential linearization strategy. The potential of this approach is proven by means of both simulations that illustrate a one-dimensional spatial optimal tracking problem and experiments that validate a zero-dimensional controlled system

Multi-scale process simulation for additive manufacturing through particle filled vat photopolymerization

The majority of research into vat photopolymerization (VP), has been focused on experimental investigations of the influence of process and material parameters. In a specific application of the VP technique, where the resin is filled with particles, this empirical approach has its limitations. In order to fully understand the relation between process parameters and the material properties a detailed numerical analysis is needed. In this paper we present a multi-scale and multi-physical simulation approach to unravel such relations in the complex production process. Using a homogenization approach, the influence of the filler particles, in this case alumina, on the light scattering, conversion characteristics and resulting effective thermal and mechanical properties is determined. The effective composite material and scattering properties are then used as input in a process simulation framework. This enables prediction of key filled-VP characteristics at a structural level. A mesh sensitivity analysis at the component scale reveals that adequate predictions may be obtained with a rather course discretization, facilitating multi-physics VP part simulations

Multiphysical modeling and optimal control of material properties for photopolymerization processes

Photopolymerization-based Additive Manufacturing (AM), a technique in which a product is built in a layerwise fashion by local curing of a liquid monomer, is increasingly being adopted by the high-tech sector. Nevertheless, industry still faces several challenges to improve the repeatability of product quality, as recognized by several authorities on AM standardization. It is commonly recognized that there is a need for an in-depth understanding, in-situ monitoring and real-time control of the curing process to work towards end-products of higher quality. This motivates the investigation on closed-loop control of the curing process and the build-up of material properties. This pioneering research contributes to the development of a control-oriented model in the form of a state-space description that describes the multiphysical photopolymerization process and connects curing kinetics, heat flow, strain and stress evolution. This work focuses on one spatial dimension and is extendable to higher dimensions. Moreover, an extension to existing control systems theory is proposed to anticipatively control the process through the quadratic tracking framework. The control strategy is based on sequential linearization of the nonlinear model obtained from multiphysical modelling. This theoretical-numerical approach demonstrates the potential of model-based control of the material property build-up during vat photopolymerization processes such as stereolithography and serves as a proof of principle

Influence of particle shape in the additive manufacturing process for ceramics

\u3cp\u3eAdditive manufacturing (AM) of ceramics through a vat photopolymerization (VP) process is a promising technique due to the high intrinsic resolution and the evanescence of stresses introduced during the layerwise additive manufacturing process. Compared to the regular vat photopolymerization process, the addition of ceramic powder increases physical complexity. Hence, large scale adoption and optimization of AM for ceramics requires a thorough understanding of the underlying physics. This work focuses on the light scattering introduced through a complex interplay between optical properties of different constituents and its effect on the photopolymerization. The effect of the shape of the ceramic particle is investigated for isolated and multiple particle cases using a parametric analysis with regular convex polygons. Although the analysis of two-dimensional isolated particle shapes indicates a preference for one shape over the other, this difference vanishes in a multiple-scattering situation. A three-dimensional analysis furthermore shows that a two-dimensional approximation of the three-dimensional scattering problem is relevant and can be used to further the process understanding of ceramic VP.\u3c/p\u3