Coupling Analysis on Microstructure and Residual Stress in Selective Laser Melting (SLM) with Varying Key Process Parameters.

Yongjian Zhang,Chunchang Wang,Kewei Xu,Fangxia Ye,Peiying Bian,Lei Li

doi:10.3390/ma15051658

Yongjian Zhang, Chunchang Wang + Show 4 more

Open Access

https://doi.org/10.3390/ma15051658

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Abstract

With the application of Selective Laser Melting (SLM) technology becoming more and more widespread, it is important to note the process parameters that have a very important effect on the forming quality. Key process parameters such as laser power (P), scan speed (s), and scanning strategy (μ) were investigated by determining the correlation between the microstructure and residual stress in this paper. A total of 10 group 316L specimens were fabricated using SLM for comprehensive analysis. The results show that the key process parameters directly affect the morphology and size of the molten pool in the SLM deposition, and the big molten pool width has a direct effect on the larger grain size and crystal orientation distribution. In addition, the larger grain size and misorientation angle also affect the size of the residual stress. Therefore, better additive manufacturing grain crystallization can be obtained by reasonably adjusting the process parameter combinations. The transfer energy density can synthesize the influence of four key process parameters (P, v, the hatching distance (δ), and the layer thickness (h)). In this study, it is proposed that the accepted energy density will reflect the influence of five key process parameters, including the scanning trajectory (μ), which can reflect the comprehensive effect of process parameters more accurately.

Highlights

Additive manufacturing (AM) has a unique forming concept and several advantages; selective laser melting (SLM) is increasingly being used in small batches of parts that are difficult to machine [1]; because of the high requirements of SLM process parameter matching, it is difficult to directly control these parameters for better product performance [2]
According to the literature [3], there are more than 130 process parameters that affect product performance, but there are five key parameters—laser power (P), scan speed (s), scanning strategy (μ), hatching distance (δ), and layer thickness (h)
As the laser power and the scanning speed were varied, the energy density imposed on the powder could be naturally changed [38]

Summary

Introduction

Additive manufacturing (AM) has a unique forming concept and several advantages; selective laser melting (SLM) is increasingly being used in small batches of parts that are difficult to machine [1]; because of the high requirements of SLM process parameter matching, it is difficult to directly control these parameters for better product performance [2]. The mismatch of these process parameters forms an unbalanced temperature field, and the resulting large temperature gradient generates high thermal stress, resulting in corresponding defects such as air gaps [4], warpage [5], cracks [6], and geometric error [7], which lead to a decrease in the mechanical properties or to the deposition failure of the formed parts. In our previous study [13], the influence of laser power and scanning strategy on residual stress distribution in 316L steel had been confirmed with a simulation combined experiment. It can be seen from the literature that the performance of the formed parts varies greatly under different combinations of processes

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