Waseda University
Deformation caused by residual stress in metal additive manufacturing fabrication technology is a major concern.
A multinational team of researchers at Waseda University have proposed a design strategy to address the challenge. The strategy involves a simultaneous optimisation of the laser scanning direction and the internal structure of the fabricated material in laser powder bed fusion-based fabrication.
According to the team, the proposed strategy has demonstrated reduction in residual deformation by up to 40% compared to benchmark designs.
In laser powder bed fusion, the molten metal generates a negative thermal stress following solidification, producing an in-plane residual stress. This can accumulate towards the upper layer with the repetitive formation process on each layer and can lead to effects such as delamination, cracking and warpage. This can make the integrated moulding of large metal parts such as rocket nozzles, challenging.
The team of Japan and USA-based researchers was led by Professor Akhiro Takezawa of Waseda University.
Takezawa said: “LPBF metal 3D printing, which has been the focus of much attention in recent years, suffers from large warping of moulded parts. In this study, we developed a method to reduce residual deformation by simultaneously optimising the internal structure of the fabricated part and the laser scanning direction.”
The study, which was made available online in October, involved Dr. Qian Chen and Professor Albert C. To from University of Pittsburgh, USA, who studied the reduction of residual warpage while focusing on layer-wise residual stacking, utilising the lattice infill distribution technique.
To analyse the residual deformation, the two employed a numerical methodology called “recurrent formula inherent strain method”. During this, they modelled the lattice based on the effective stiffness and anisotropic inherent strain using a gradient-based optimisation algorithm.
The team optimised two aspects of the fabrication process, the scanning direction that utilises asymmetry of residual stress, and the internal structure of the fabricated material with layer-wise residual stress stacking. The team says they fine-tuned the methodology to ensure the synergetic influence of simultaneous optimisation.
Compared to the standard benchmark designs in use, the design strategy reduced vertical edge deformations by 23-39% in quasi-2D plates according to the team. In cases of 3D brackets and connecting rods, the team said the warpage reductions ranged between 13-20%.
The team believes that the methodology could herald a remarkable development in 3D printing with LPBF fabrication.
Takezawa said: “Recent improvements in metal 3D printing technology have made it possible to produce larger moulded parts. In this light, our methodology should ideally enable 3D printing of any large metal part.”
