Mechanics Modeling of Residual Stress Considering Effect of Preheating in Laser Powder Bed Fusion

Elham Mirkoohi,You-Cheng Chang,Hung-Yu Lin,Steven Y Liang,Hong-Chuong Tran,Yu-Lung Lo

doi:10.3390/jmmp5020046

Abstract

This study aimed at the investigation of the effect of substrate temperature on residual stress in laser powder bed fusion using a physics-based analytical model. In this study, an analytical model is proposed to predict the residual stress through the calculation of preheating affected temperature profile and thermal stress. The effect of preheating is super-positioned with initial temperature in the modeling of temperature profile using a moving heat source approach; the resultant temperature gradient is then employed to predict the thermal stress from a point body load approach. If the thermal stress exceeds the yield strength of the material, then the residual stress under cyclic heating and cooling will be calculated based on the incremental plasticity and kinematic hardening behavior of metal. IN718 is used as a material example to pursue this investigation. To validate the predicted residual stress, experimental measurements are conducted using X-ray diffraction on IN718 samples manufactured via laser powder bed fusion under different process conditions. Results showed that preheating of the substrate could reduce the residual stress in an additively manufactured part due to the reduction in temperature gradient and resultant shrinkage stresses. However, the excessive preheating could have an opposite impact on residual stress accumulation. Moreover, the results confirm that the proposed model is a valuable tool for the prediction of residual stress, eliminating the costly experiments and time-consuming finite element simulations.

Highlights

Metal additive manufacturing (AM), in which the near net shape parts and assemblies are built up from a high precision laser, has become an important technology in the past few years to manufacture 3D components [1]
The metal additive manufacturing can be divided into two main categories of powder feed (PF) system in which the powders are carried out via nozzles; and powder bed fusion (PBF-LB) in which the powders are sat on a bed to be melted selectively [2]
Sames et al indica3toefd11 that the highest stress concentration is located near the interface between substrate and SLM-processed part. These results indicate that the interface between substrate and part isintheelimloicnaattioionns owf hdeisrteortthioenpfarrotmha1s0.m6 morme p(wositshiboiulittyprteohedaetlianmg)in[1a8te]. dSuamrinegs eStLaMl. inpdroiccaetsesd [1t9h]a.t the highest stress concentration is located near the interface between substrate and SLMT-oprtohceebsseesdt opfatrht.eTahuetsheorress’uklntsoiwndleidcagtee, tthhaetrethies innotewrfaocrek bthetawt espenecsiufibcsatlrlyatemaonddelpsatrhteis eftfheectloocfaptiroenhseawtihnegreotfhseupbastrrtahteasomn orerseidpuosaslisbtirleitsys tion dmeelataml iAnaMteadnudrivnagliSdLaMtesptrhoactevssia[1e9x]-. perimeTnotathtieonb.est of the authors’ knowledge, there is no work that models the Tehffeecptuorfpposreehoefatthinegcuorfresuntbswtroartke iosntoreinsivdeustailgasttreetshseinimmpeatcatloAf Mpreahnedatvinaglidteamtepsetrhaa- t tuvriea eoxnpreersiimdeunatlasttiroens.s formation during additive manufacturing of Inconel 718 (IN718)

Summary

Introduction

Metal additive manufacturing (AM), in which the near net shape parts and assemblies are built up from a high precision laser, has become an important technology in the past few years to manufacture 3D components [1]. The simulation of residual stress considering multi-layer and multi-scan aspects of AM process using the proposed model takes less than two and a half minutes to be completed using a 2.3 GHz core i5 laptop compared to hours of calculations using finite element modeling since it involves no iteration, nor meshing. Such models can be extended to model the microstructure of the additively manufactured part. Alimardani et al [14] proposed a numerical model to investigate the effect of pre-heating on residual stress in additive manufacturing of 304 L stainless-steel. If Fyeild > 0, incremental plastic strains are calculated and accumulated during the stress history to determine the total plastic strains using modified McDowell algorithm [23]

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Results and Discussion