Manufacturing-oriented topology optimization has been extensively studied the past two decades, in particular for the conventional manufacturing methods, for example, machining and injection molding or casting. Both design and manufacturing engineers have benefited from these efforts because of the close-to-optimal and friendly-to-manufacture design solutions. Recently, additive manufacturing (AM) has received significant attention from both academia and industry. AM is characterized by producing geometrically complex components layer-by-layer, and greatly reduces the geometric complexity restrictions imposed on topology optimization by conventional manufacturing. In other words, AM can make near-full use of the freeform structural evolution of topology optimization. Even so, new rules and restrictions emerge due to the diverse and intricate AM processes, which should be carefully addressed when developing the AM-specific topology optimization algorithms. Therefore, the motivation of this perspective paper is to summarize the state-of-art topology optimization methods for a variety of AM topics. At the same time, this paper also expresses the authors' perspectives on the challenges and opportunities in these topics. The hope is to inspire both researchers and engineers to meet these challenges with innovative solutions.

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Current and future trends in topology optimization for additive manufacturing

Topology optimization is a highly developed tool for structural design and is by now being extensively used in mechanical, automotive and aerospace industries throughout the world. Gradient-based topology optimization algorithms may efficiently solve fine-resolution problems with thousands and up to millions of design variables using a few hundred (finite element) function evaluations (and even less than 50 in some commercial codes). Nevertheless, non-gradient topology optimization approaches that require orders of magnitude more function evaluations for extremely low resolution examples keep appearing in the literature. This forum article discusses the practical and scientific relevance of publishing papers that use immense computational resources for solving simple problems for which there already exist efficient solution techniques.

On the usefulness of non-gradient approaches in topology optimization

Delamination formation, evaluation and suppression during drilling of composite laminates: A review

Concurrent topology optimization design of material and structure within FE2 nonlinear multiscale analysis framework

A review of topology optimization for additive manufacturing: Status and challenges

Ultra-light cellular materials exhibit high stiffness/strength to weight ratios and bring opportunity for multifunctional performance. One of their potential applications is to build structure with optimum dynamic performance, which is extremely important for some structural parts in vehicle engineering and attracts a great attention. This paper presents a two-scale optimization method and aims at finding optimal configurations of macro structures and micro-structures of cellular material with maximum structural fundamental frequency. In this method macro and micro densities are introduced as independent design variables for macrostructure and microstructure. Optimizations at two scales are integrated into one system through homogenization theory and base material is distributed between the two scales automatically with optimization model. Microstructure of materials is assumed to be homogeneous at the macro scale to meet today’s manufacture practice and reduce manufacturing cost. Plane structure with homogeneous cellular material and perforated plate are studied. Numerical experiments validate the proposed method and computational model.

Optimum structure with homogeneous optimum cellular material for maximum fundamental frequency

Drilling holes on CFRP components is inevitable for assembling process in the aviation industry. The drilling-induced damages frequently occur and affect not only the load carrying capacity of components but also the reliability. Therefore, it is of great urgency to enhance drilling quality on CFRP components. The article aims to propose a novel drill structure to change the cutting conditions at the drill exit and effectively reduce damages in drilling CFRP. Considering the drilling-exit constraint condition, a unique two-dimensional cutting model is established to represent the axial cutting of the main cutting edge at the drill exit. Based on the model, the effects of point of action and cutting direction on material removal at the exit are investigated, and the result indicates that cutting CFRP in the upward direction has positive effects on deflection limitation and damage reduction. In order to perform the upward cutting, a novel intermittent-sawtooth drill structure is proposed on the one-shot drill. The theoretical and geometrical analyses of the drilling process reveal that the cutting lips of the structure could reverse the cutting direction from downward to upward and thereby, reduce the drill-exit damages. Furthermore, drilling experiments are conducted and the drill structure is proved to be effective to reduce drilling damages as expected.

Novel drill structure for damage reduction in drilling CFRP composites

Discrete material optimization of vibrating laminated composite plates for minimum sound radiation

Carbon fiber reinforced polymer composite laminates are anisotropic, inhomogeneous, and mostly prepared in laminate form before undergoing the finishing operations. The edge trimming process is considered as one of the most common finishing operations in the industrial applications. However, the laminate surface is especially prone to damage in the chip formation process, and the most common damage mode is burrs. Burrs may increase cost and production time because of additional machining; they can also damage the surface integrity. Many studies have been done to address this problem, and techniques for reducing burr size in material removal process has been the focus of the research. Nonetheless, the combined effects of the cutting edge radius and the fiber cutting angle on the burr formation have seldom been conducted, which in turn restricts to find out the mechanism of burr formation. The purpose of the present paper is to study the particular mechanism that leads to burr formation in edge trimming of CFRP laminates and investigate the effects of fiber cutting angle and cutting edge radius on burr formation. The results indicate that the burrs are prone to form in the fiber cutting angle range of 0° < χ < 90° when a large cutting edge radius of the tool is used for both milling and drilling of CFRP composites.

Bin Niu

Papers

Optimum structure with homogeneous optimum cellular material for maximum fundamental frequency

Novel drill structure for damage reduction in drilling CFRP composites

Discrete material optimization of vibrating laminated composite plates for minimum sound radiation

Effects of cutting edge radius and fiber cutting angle on the cutting-induced surface damage in machining of unidirectional CFRP composite laminates

Optimum design of band-gap beam structures