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New design strategy to reduce deformation in AM parts

Researchers have developed a design strategy that reduces the deformation caused by residual stresses in additively manufactured parts by up to 40%.

The improvements, verified through testing, could herald a remarkable development in 3D printing using LPBF fabrication, according to the researchers. 

As molten metal solidifies during laser powder bed fusion (LPBF), residual stresses accumulate with the formation of each layer, often leading to undesirable effects such as delamination, cracking, and warpage.

Such deformations are asymmetric in nature and scale with the size of the fabricated metal part, making the moulding of large metal parts – such as rocket nozzles – extremely challenging. Reduction in residual warping and deformation is therefore critical to moulding large metal components.

To address this, the team of researchers, led by Professor Akihiro Takezawa from Waseda University in Tokyo, Japan, have proposed and published an optimised design strategy in Additive Manufacturing.

“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,” Takezawa explained.

The scientists studied the reduction of residual warpage while focusing on layer-wise residual stacking and using a ‘lattice infill distribution technique’. A numerical ‘recurrent formula inherent strain method’ was also employed to analyse the residual deformation. In doing this, the researchers modelled the lattice based on the effective stiffness and anisotropic inherent strain using a gradient-based optimisation algorithm.

As mentioned by Takezawa, the team were able to simultaneously optimise two aspects of LPBF. The laser ‘hatching orientation’ (scanning direction) was optimised in a way that the asymmetry of residual stress could be utilised, while the internal structure of the fabricated material was optimised through consideration of layer-wise residual stress stacking.

Simultaneous optimisation of hatching orientations and lattice density distriubution for residual warpage redcution in LPBF considering layerwise residual stress stacking. (Image: Takezawa et al.)

The team performed experiments to verify their novel methodology using quasi-2D plates, 3D brackets, and 3D connecting rods. Compared to the standard benchmark designs in use, their design strategy reduced vertical edge deformations by 23-39% in quasi-2D plates, while for 3D brackets and connecting rods the warpage reductions ranged between 13-20%.

Overall, the methodology proposed in the study could herald a remarkable development in LPBF fabrication, according to the researchers. 

“Recent improvements in metal 3D printing technology have made it possible to produce larger moulded parts,” concluded Takezawa. “In this light, our methodology should ideally enable 3D printing of any large metal part.”