Minting Wang, Renjie Cao, HuiChao Chang and Dong Liang
Laser-based powder bed fusion (LPBF) is a new method for forming thin-walled parts, but large cooling rates and temperature gradients can lead to large residual stresses and…
Abstract
Purpose
Laser-based powder bed fusion (LPBF) is a new method for forming thin-walled parts, but large cooling rates and temperature gradients can lead to large residual stresses and deformations in the part. This study aims to reduce the residual stress and deformation of thin-walled parts by a specific laser rescanning strategy.
Design/methodology/approach
A three-dimensional transient finite element model is established to numerically simulate the LPBF forming process of multilayer and multitrack thin-walled parts. By changing the defocus amount, the laser in situ annealing process is designed, and the optimal rescanning parameters are obtained, which are verified by experiments.
Findings
The results show that the annealing effect is related to the average surface temperature and scan time. When the laser power is 30 W and the scanning speed is 20 mm/s, the overall residual stress and deformation of the thin-walled parts are the smallest, and the in situ annealing effect is the best. When the annealing frequency is reduced to once every three layers, the total annealing time can be reduced by more than 60%.
Originality/value
The research results can help better understand the influence mechanism of laser in situ annealing process on residual stress and deformation in LPBF and provide guidance for reducing residual stress and deformation of LPBF thin-walled parts.
Details
Keywords
Huichao Wang, Qin Lian, Dichen Li, Chenghong Li, Tingze Zhao and Jin Liang
Reconstructing multi-layer tissue structure using cell printing to repairing complex tissue defect is a challenging task, especially using in situ bioprinting. This study aims to…
Abstract
Purpose
Reconstructing multi-layer tissue structure using cell printing to repairing complex tissue defect is a challenging task, especially using in situ bioprinting. This study aims to propose a method of in situ bioprinting multi-tissue layering and path planning for complex skin and soft tissue defects.
Design/methodology/approach
The scanned three-dimensional (3D) point cloud of the skin and soft tissue defect is taken as the input data, the depth value of the defect is then calculated using a two-step grid division method, and the tissue layer is judged according to the depth value. Then, the surface layering and path planning in the normal direction are performed for different tissue layers to achieve precise tissue layering filling of complex skin soft tissue defects.
Findings
The two-step grid method can accurately calculate the depth of skin and soft tissue defects and judge the tissue layer accordingly. In the in situ bioprinting experiment of the defect model, the defect can be completely closed. The defect can be reconstructed in situ, and the reconstructed structure is basically the same as the original skin tissue structure, proving the feasibility of the proposed method.
Originality/value
This study proposes an in situ bioprinting multi-tissue layering and path planning method for complex skin and soft tissue defects, which can directly convert the scanned 3D point cloud into a multi-tissue in situ bioprinting path. The printed result has a similar structure to that of the original skin tissue, which can make cells or growth factors act on the corresponding tissue layer targets.
Details
Keywords
Xuemei Li, Shiwei Zhou, Kedong Yin and Huichao Liu
The purpose of this paper is to measure the high-quality development level of China's marine economy and analyze corresponding spatial and temporal distribution characteristic.
Abstract
Purpose
The purpose of this paper is to measure the high-quality development level of China's marine economy and analyze corresponding spatial and temporal distribution characteristic.
Design/methodology/approach
Design and optimize the index system of high-quality development level of marine economy and use entropy and TOPSIS method for comprehensive evaluation.
Findings
The research finds that from 2017 to 2019, the high-quality development tendency of China's marine economy is on the rise, but the overall level is still low. The level of each subsystem has different distribution characteristics in different provinces and cities. Guangdong, Shandong and Shanghai have a high comprehensive level. According to the comprehensive level of high-quality development of marine economy, 11 coastal provinces are divided into three types: leading, general and backward.
Research limitations/implications
This paper clarifies the temporal and spatial distribution law of high-quality development level of China's marine economy, providing basis for promoting comprehensive and coordinated improvement of coastal provinces and cities.
Originality/value
An indicator system for the high-quality development level of the marine economy has been established, including social development guarantee, marine economic foundation, marine science and technology drive and green marine sustainability.