Additive Manufacturing (AM) is prepared by layer by layer accumulation of material. This unique manufacturing approach enables the free &ldquo of highly complex structures; grows ” forms; greatly expands the design of “ space ” provides a powerful tool for the preparation of new structures and materials. However, most of the existing materials manufacturing structures still adopt the design configuration oriented to the traditional manufacturing process. In this way, the fabricated structures do not take full advantage of the new design space provided by the incremental manufacturing, and the performance can not be substantially improved. Even limited to the immaturity of the incremental manufacturing technology, the performance is inferior to the structure prepared by the traditional manufacturing process.
Topology optimization, because it does not depend on the initial configuration and the engineer's experience, can achieve completely unexpected innovative configuration, and has attracted widespread attention of scholars and engineers. generally speaking, topology optimization is the use of optimization methods to find the structure of the interior, where the materials need to be arranged and what materials are arranged, so as to obtain the optimal performance under certain constraints.
Fig. 1 Schematic diagram of topology optimization
However, the geometric structure of topology optimization is complex, and it is very difficult to prepare by traditional manufacturing process. Therefore, there is still a big gap between the topology optimization method and the actual engineering structure design. Designers often based on manufacturing technology and experience to optimize the results of the two design, to meet manufacturability, reduce manufacturing costs. This approach often damages the optimality of structures, and the resulting structural properties can not even reach the existing configuration. On the other hand, subject to the traditional concept of design and manufacturing process, the structure is often only macro topology design, broad design space did not make use of the structure in multi-scale changes or spatial gradient caused by changes of the product performance is very limited.
The appearance of wood based manufacturing technology makes geometric forms highly complex and makes possible the preparation of multiple geometric scale structures from micro to macro. It subverts the limitations of traditional manufacturing technology, solves the problem of &ldquo in product development, and decides the design of &rdquo.
Therefore, the integration of topology optimization (advanced design technology) with timber manufacturing (Advanced Manufacturing Technology) and the development of innovative design technology have broad prospects, and have attracted widespread attention in the academic community. Aviation structural innovation research and development has the characteristics of small batch, multi varieties, high performance and so on. Breaking through the existing design limits puts forward higher requirements for structural innovation design technology and rapid trial manufacture technology. As a kind of &ldquo, &rdquo has become the core technology of &ldquo. It can greatly reduce the R & D cycle and cost, and it is the core technology of &rdquo.
The integration of the whole structure, the gradient of material properties, the integration of functional structure and the multifunction of structure have become the important development direction of new structures and materials. Increase in material manufacturing process based on &ldquo, a breakthrough in the traditional design; limit ” overall, R & D, lightweight, low cost and high performance of the new structure and material is a new generation of major / high-end equipment and design demand. This section will mainly introduce the design of innovative high-quality structural configurations from 4 aspects based on topology optimization methods.
Composite materials have attracted much attention because of their unique properties and good design ability. It has become a hot spot in the field of materials to obtain periodic composites with specific or special properties by designing microstructures. The new materials obtained in this way are often referred to as structural materials. Topology optimization technology provides a powerful tool for the design of micro structure, and has carried out extensive research. The fabrication of high-performance structural materials based on wood based manufacturing technology has become a frontier issue of research.
Schematic diagram of micro structure configuration based on topology optimization
Multilayer structure design refers to the design of the structure at the macro and micro levels of the structure at the same time, as shown in the diagram, which can effectively expand the design space, and is conducive to obtain excellent structural configuration.
Schematic diagram of multilayer structure design
Ultra light metal lattice material
Skeletal reconstruction based on multilevel structure design
After 10 years' silence, the topology optimization design of multilayer structure has entered a new research upsurge because of the rapid development of timber manufacturing. However, the existing methods are still faced with many difficulties, such as design variables, such as high computational complexity, how to balance in the design space and computational efficiency, methods used for the design of engineering structures remains a challenge. In addition, most of the existing designs are based on homogenization methods, which are equivalent to homogeneous materials without considering the size effects of structures.
Through the rational layout of materials, the distribution of material properties according to the needs, can greatly improve the structural performance, as shown.
Schematic diagram of multi material structure
Example of flexible mechanism
Multi material topology optimization method has been mature gradually after 20 years of development. However, the research on the interface defects and the influence of the gradient layer is still lacking, which needs further study. In addition, due to technological limitations, the existing multi material topology optimization is mainly for homogeneous multi material partition configuration design, emerged in recent years, increasing material manufacturing technology can be changed by different materials in different locations of the component proportion change of material properties in space. Therefore, the technology of wood based manufacturing provides the possibility for the preparation of multi material configurations with arbitrary gradients, which greatly releases the design space of researchers. Therefore, how to make full use of the design space released by wood increment and take into account the fabrication process constraints of multi material configuration is an important research direction of multi material layout optimization in the future.
In addition to the load-bearing function, the complex component stage structure also includes heat dissipation, vibration reduction, stealth and conduction. It is an effective way to improve the structure performance by reasonably designing the structure configuration and realizing the multi functions. Based on the technology of wood based manufacturing, a new structure with complex cavities and multiple materials can be prepared, so that components with bearing and other functions are expected to be realized. In view of this, many scholars have carried out the research of topology optimization design of multi-function structure, such as vibration reduction, noise reduction, bearing heat dissipation, conduction and antenna structure design.
Antenna design of ground penetrating radar
Although multi function structure design based on topology optimization has been developed vigorously, it is difficult to analyze and solve multiple physical fields. Most of the existing designs focus on 2~3 independent physical fields. Considering the multi physics field coupling and multi-objective topological optimization design method is still in the initial stage of research. In order to realize the engineering application of design results, this direction will become the focus of the next research.
Compared with the traditional manufacturing process, the wood based manufacturing technology can realize the fabrication of complex geometric configurations because of its unique manufacturing methods. However, additive manufacturing is not completely free of “ ” manufacturing, there are still constraints unique, mainly include the following categories: maximum / minimum structure size, supporting structure, manufacturing defects (surface roughness and material anisotropy) and connectivity constraints etc.. It has become the focus of scholars both at home and abroad that how to consider the process constraints and realize the rapid and direct preparation of the topology optimization results in the process of topology optimization.
Different 3D printing devices have different print accuracy, so it is necessary to control the feature size of topology optimization results to avoid the appearance of thin bars which can not be manufactured. Figure 10 shows the topology optimization results without considering the minimum size feature control and considering the minimum size feature control. As we can see, for the fine structure in Figure 10 (a), it is difficult to prepare [17-18] for some printers which are not of high precision. Since the dimension constraint exists in the traditional manufacturing process, the direction has been paid much attention to by scholars, and a relatively perfect method of dimension control system for topology optimization has been established.
Size characteristic control of topology optimization
In the process of incremental manufacturing, for large cantilever structures, it is often necessary to add support structures below them to prevent structural collapse in manufacturing engineering, as shown. The use of supporting structure will not only bring about the increase of printing time and cost, but also bring about the difficulty of process and influence the final surface precision of structure at the later stage. Therefore, the design of self support structure, in the optimization process, automatic identification of feature structure, avoid large cantilever structure, has become the focus of research.
Some scholars have made a preliminary exploration in this direction, however, the existing models are based on theoretical assumptions, structural collapse limit and material properties, overhanging angle and cantilever length, not by a lot of experiments obtained.
In recent years, although the technology of material gain has been developed rapidly, as a whole, the manufacturing process is still in the initial stage of technology, not yet mature. Due to process limitations, there are many defects in structural parts, such as material anisotropy, surface roughness, and uncertainty of material properties. In view of this problem, some scholars take the manufacturing defects into account in the topology optimization model,
Sketch of large cantilever structure and supporting structure
To reduce the effect of defects on structural properties. However, most of the defect models used in the calculation process are theoretical models, which do not agree with the uncertainty models caused by the incremental manufacturing process. Therefore, it is the future research target to establish the true defect model and introduce it into the topology optimization process based on the experimental study of the material forming mechanism of the material manufacturing.
The supporting structure can not be removed inside the enclosed structure
Design structure with consideration of different connectivity constraints
Increase in material manufacturing process, whether using fused deposition modeling (FDM) or selective laser sintering powder technology (SLS), all need to remove the support material in the structure after printing or metal powder does not melt, thus requires not internal structure with internal hole closed. The structure containing internal hole, because the metal powder can not be removed or support material does not melt, often need two amendment or partition structure manufacturing, greatly increasing the difficulty of manufacture process, increase the cost of.
With the rapid development of increase in material manufacturing process, for increasing innovation design theory and method of material manufacturing, with manufacturing (Design for manufacturing) quality configuration (configuration design quality), has become a new topic faced by today's designers and researchers. Topology optimization technology after decades of development, has been in the high quality design configuration (structural material, multilayer structure, material structure and multifunctional structure) to carry out extensive research, can make full use of additional material manufacturing technology innovation design release great space. How will the topology optimization (advanced design tools) and additional material manufacturing technology (advanced tool preparation) combined with the rapid promotion of architecture innovation ability, will become a hot point in the next 10 years of research.