Additively manufactured parts experience many more heating and cooling cycles than traditionally manufactured materials [1]. This effect is even more pronounced in processes such as Directed Energy Deposition (DED) due to their higher thermal gradients. One of the adverse consequences of these repeated heat cycles is reduced geometrical accuracy [2]. This can lead to issues such as the need for larger tolerances that increase material costs or excessive deformation that makes the produced part unusable. Therefore, achieving near-net-shape parts remains a major challenge in additive manufacturing.

Changing the laser mode from the usual continuous wave (CW) to pulsed wave (PW) significantly influences the amount of heat generated and absorbed by the material [3]. Adjusting the frequency and duty cycle of the PW laser mode allows further control over the heat input during deposition [4, 5]. However, limited research has focused on how PW laser parameters affect thermal behaviour, distortion, and residual stress formation in DED-fabricated parts.

This study aims to understand how using a PW laser affects parts fabricated via the DED process, with the goal of identifying PW as a fast and straightforward alternative to CW mode for achieving higher geometrical accuracy. Multiple thin-wall samples are first deposited under identical conditions and then heat treated to remove residual stresses. These stress-free walls serve as reference bases for Digital Image Correlation (DIC) analysis, enabling a direct comparison of deformation across samples. Each wall is then repositioned, and a post-wall is deposited under different PW laser settings (varying frequency and duty cycle). By analysing how each post-wall deposition affects deformation, we assess whether the use PW laser can effectively reduce distortion and what implications this has for residual stress.

As shown in Figure 1, DIC strain measurements indicate a reduction in strain in both the scanning and build directions. These preliminary results suggest that PW laser operation can effectively reduce distortion in DED-fabricated parts. Ongoing work will further quantify these effects and assess their implications for distortion and residual stress. 

References

[1] N. S. Rossini; Materials & Design, 2012, 35, 572-588.

[2] Y. Liu; Advanced Engineering Materials, 2023, 25.

[3] M. Cheng; Materials, 2023, 16, 6610.

[4] X. Zou; Optics & Laser Technology, 2022, 150, 107910.

[5] Z. Yan; Materials, 2024, 17, 5231.