# Lightweight Research in Engineering: A Review
## 4 Lightweight Pathways and Research Progress
### Lightweight Manufacturing Technology and 3D Printing  
Lightweight materials are only one aspect of research. When new materials are identified, new production processing conditions are needed to reduce weight. The organic integration of new material and new technology into product development not only improves the product performance, but also effectively shortens the production time and material consumption of the product and shortens the whole life cycle of the product. The development and research of new technology has pointed out a new way for lightweight. The optimization of lightweight manufacturing technology can be divided into cutting, welding, and improvement of other processes of Tox connection. Cutting technology is mainly considered to adopt advanced equipment or improved process method to improve the machining accuracy and efficiency. In welding technology, besides using advanced welding equipment, good welding technology can not only improve the welding strength, but also make the appearance of welding neat and beautiful. The 3D Kagome lattice structure, 3D pyramid structure, and hexagonal diamond structure were designed. The selected material was fabricated by using an Objet 350 3D printer and a polypropylene-based photopolymer called Objet Durus White RGD430 in 2014 [135]. In 2016, [PERSON] et al. [136] proposed a density-aware internal support structure modeling scheme in order to realize the lightweight modeling of 3D-printing model which conforms to the mechanical characteristics. The Density-Controllable internal support structure was generated according to the structural analysis. Simultaneously, [PERSON] et al. [137] proposed a \"weak balance\" lightweight modeling scheme, to generate the internal filling structure of 3D printing model. The scheme can generate internal density-varying fillings based on structural analysis automatically. The lattice structure has many properties superior to solid materials and traditional structures. It can integrate many functions. [PERSON] and [PERSON] [138] used AM technology to make a computer-aided design model, which is more complex than the traditional program, by adding materials layer by layer. In 2017, [PERSON] et al. [139] introduced a new type of additive manufacturing technology for fiber reinforced thermoplastic composites, namely ultra-lightweight continuous lattice manufacturing, and demonstrated its ability to characterize anisotropic materials in digital manufacturing structures. [PERSON] et al. [140] used topology optimization as an innovative design tool, to facilitate additives manufacturing, by adding materials layer by layer, to achieve complex geometry. Almost any product can be manufactured, and the best product structure can be created with the least amount of materials, but can still ensure the product attributes of machinery. [PERSON] et al. [35] applied topological optimization method and size optimization to find the best path of force transmission and the optimum cross-section size of truss members for the lightweight design of satellite structures. Considering the optimum rod size of truss members and the constraints of structural processing, geometric reconstruction was carried out to obtain the structural design scheme for material-added manufacturing to achieve lightweight design. [PERSON] et al. [141] generated honeycomb path trajectories with controllable parameters based on material and compressive stress analysis. An adaptive generation technology of lightweight honeycomb 3D-printing path was proposed, which provided a new idea for direct printing generation of lightweight structure with improved local load-carrying performance in 2018. A novel compression-resistant lattice composite material by introducing a novel optimization method and metallization method was proposed [142], which made a great contribution to lightweight in 2019. Based on the bionics principle, [PERSON] et al. [131] designed the bionic robot thigh according to the CT scan human-femur surface.