# Lightweight Research in Engineering: A Review
## 4 Lightweight Pathways and Research Progress
### Structure Lightweight
#### 4.2.1 Size Lightweight  
Size lightweight refers to the optimization of the basic dimension structure by means of mechanical analysis. It means that the basic shape and size of the components have been determined, and the functions of the products have also been realized in order to improve performance and reduce costs. Many different types of sizes can be selected for optimization, and we can optimize the critical size (dimensions) of the product. Generally, the optimal size selection is based on the required functional and mechanical properties constraints to select the optimal combination from a certain limited range. A lightweight design method for automobile body structure based on sensitivity analysis and side collision was proposed [27]. The thickness of the body structure parts is taken as the design variable, the modality and rigidity of the body-in-white are the constraints, and the body-in-white mass is the minimum. The sensitivity of the part thickness to the modality and stiffness of the body is analyzed. The thickness of the body parts that are insensitive to the modality and stiffness of the vehicle body and the crashworthiness are selected to optimize the calculation with the minimum body mass. The result of the optimization reduced the body by 14.8 kg. The simulation calculation of the side collision is carried out on the lightweight vehicle and occupant restraint system, and compared with the results before the lightweight, the vehicle crashworthiness and the safety of the occupant are compared and checked, according to the collision result. The thickness of the body parts was readjusted. The results show that the lightweight body meets the requirements of collision safety, and the dummy's C-NCAP score is acceptable. In 2014, [PERSON] et al. [28] established the multidisciplinary design optimization model of the vehicle door, analyzed the sensitivity of the design variables, removed the design variables that had less influence on the structure, constructed the approximate response surface of each performance, and applied the genetic algorithm based on the response surface for multidisciplinary optimization. [PERSON] et al. [29] used the three-dimensional SolidWorks drawing software to establish a three-dimensional model of the gantry machining center. The key dimension sensitivity analysis of the V-shaped rib beam structure was carried out, and the beam size design was carried out by the extreme dimension adjustment method. During 2015, the shape and size of the ship's bottom slab and the upper building slab were optimized, to seek the optimal distribution of materials. Based on the above mentioned data, the volume fraction is set as the restriction condition of the model, and the structural natural frequency is set as the objective function [30]. [PERSON] et al. [31] took the wall thickness length and transition angle of each section of hollow half-axle of automobile steering drive axle as design variables, the minimized quality of half-axle as optimization objective, and the second-order constrained mode frequency and equivalent stress at the end corner transition of half-axle spline as constraints, established a lightweight optimization model of half-axle. A combination of 10 design variables and three levels of numerical simulation tests was obtained by using an orthogonal experimental design. The response surface approximation model was established by the least-squares method, and the model was optimized by the sequence quadratic programming algorithm. [PERSON] et al. [32] carried out a study on the optimization of the machine tool column topology. According to the results of the material distribution, the basic shape of the machine tool column was designed. Five different types of stiffened plate structures were compared. It was found that the material consumption of the W-type stiffened plate structure was less and the comprehensive mechanical properties were better.