Experimental Analysis of Residual Stresses on AlSi10Mg Parts Produced by Means of Selective Laser Melting (SLM)

Purpose During the powder bed fusion process, thermal distortion is one big problem owing to the thermal stress caused by the high cooling rate and temperature gradient. For the purpose of avoiding distortion caused by internal residual stresses, support structures are used in most selective laser melting (SLM) process especially for cantilever beams because they can assist the heat dissipation. Support structures can also help to hold the work piece in its place and reduce volume of the printing materials. The mitigation of high thermal gradients during the manufacturing process helps to reduce thermal distortion and thus alleviate cracking, curling, delamination and shrinkage. Therefore, this paper aims to study the displacement and residual stress evolution of SLMed parts. Design/methodology/approach The objective of this study was to examine and compare the distortion and residual stress properties of two cantilever structures, using both numerical and experimental methods. The part-scale finite element analysis modeling technique was applied to numerically analyze the overhang distortions, using the layer-by-layer model for predicting a part scale model. The validation experiments of these two samples were built in a SLM platform. Then average displacement of the four tip corners and residual stress on top surface of cantilever beams were tested to validate the model. Findings The validation experiments results of average displacement of the four tip corners and residual stress on top surface of cantilever beams were tested to validate the model. It was found that they matched well with each other. From displacement and residual stress standpoint, by introducing two different support structure, two samples with the same cantilever beam can be successfully printed. In terms of reducing wasted support materials, print time and high surface quality, sample with less support will need less post-processing and waste energy. Originality/value Numerical modeling in this work can be a very useful tool to parametrically study the feasibility of support structures of SLM parts in terms of residual stresses and deformations. It has the capability for fast prediction in the SLMed parts.

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Effect of Process Parameters and High-Temperature Preheating on Residual Stress and Relative Density of Ti6Al4V Processed by Selective Laser Melting

Materials ◽

10.3390/ma12060930 ◽

2019 ◽

Vol 12 (6) ◽

pp. 930 ◽

Cited By ~ 12

Author(s):

Martin Malý ◽

Christian Höller ◽

Mateusz Skalon ◽

Benjamin Meier ◽

Daniel Koutný ◽

...

Keyword(s):

Residual Stress ◽

High Temperature ◽

Residual Stresses ◽

Relative Density ◽

Selective Laser Melting ◽

Process Parameters ◽

Stress Reduction ◽

Laser Melting ◽

Preheating Temperature ◽

Laser Velocity

The aim of this study is to observe the effect of process parameters on residual stresses and relative density of Ti6Al4V samples produced by Selective Laser Melting. The investigated parameters were hatch laser power, hatch laser velocity, border laser velocity, high-temperature preheating and time delay. Residual stresses were evaluated by the bridge curvature method and relative density by the optical method. The effect of the observed process parameters was estimated by the design of experiment and surface response methods. It was found that for an effective residual stress reduction, the high preheating temperature was the most significant parameter. High preheating temperature also increased the relative density but caused changes in the chemical composition of Ti6Al4V unmelted powder. Chemical analysis proved that after one build job with high preheating temperature, oxygen and hydrogen content exceeded the ASTM B348 limits for Grade 5 titanium.

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Evaluation of the impact of scanning strategies on residual stresses in selective laser melting

The International Journal of Advanced Manufacturing Technology ◽

10.1007/s00170-019-03396-9 ◽

2019 ◽

Vol 102 (5-8) ◽

pp. 2441-2450 ◽

Cited By ~ 19

Author(s):

L. Mugwagwa ◽

D. Dimitrov ◽

S. Matope ◽

I. Yadroitsev

Keyword(s):

Residual Stresses ◽

Selective Laser Melting ◽

Laser Melting ◽

Scanning Strategies ◽

The Impact

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Improvement of the bridge curvature method to assess residual stresses in selective laser melting

Additive Manufacturing ◽

10.1016/j.addma.2018.05.025 ◽

2018 ◽

Vol 22 ◽

pp. 320-329 ◽

Cited By ~ 9

Author(s):

Sabine Le Roux ◽

Mehdi Salem ◽

Anis Hor

Keyword(s):

Residual Stresses ◽

Selective Laser Melting ◽

Laser Melting

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Investigation of Sectoral Scanning in Selective Laser Melting

ASME 2010 10th Biennial Conference on Engineering Systems Design and Analysis, Volume 4 ◽

10.1115/esda2010-24621 ◽

2010 ◽

Cited By ~ 10

Author(s):

Evren Yasa ◽

Jan Deckers ◽

Jean-Pierre Kruth ◽

Marleen Rombouts ◽

Jan Luyten

Keyword(s):

Mechanical Properties ◽

Residual Stresses ◽

Laser Beam ◽

Surface Quality ◽

Selective Laser Melting ◽

Random Order ◽

Laser Source ◽

Metal Powders ◽

Laser Melting ◽

Powder Bed

Selective laser melting (SLM), a powder metallurgical (PM) additive manufacturing (AM) technology, is able to produce fully functional parts directly from standard metal powders without using any intermediate binders or any additional post-processing steps. During the process, a laser beam selectively scans a powder bed according to the CAD data of the part to be produced and completely melts the powder particles together. Stacking and bonding two-dimensional powder layers in this way, allows production of fully dense parts with any geometrical complexity. The scanning of the powder bed by the laser beam can be achieved in several different ways, one of which is island or sectoral scanning. In this way, the area to be scanned is divided in small square areas (‘sectors’) which are scanned in a random order. This study is carried out to explore the influence of sectoral scanning on density, surface quality, mechanical properties and residual stresses formed during SLM. The experiments are carried out on a machine with an Nd:YAG laser source using AISI 316L stainless steel powder. As a result of this experimental study, it is concluded that sectoral scanning has some advantages such as lower residual stresses and better surface quality. However, the selection of parameters related to sectoral scanning is a critical task since it may cause aligned porosity at the edges between sectors or scanned tracks, which is very undesired in terms of mechanical properties.

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Residual stresses in selective laser sintering and selective laser melting

Rapid Prototyping Journal ◽

10.1108/13552540610707013 ◽

2006 ◽

Vol 12 (5) ◽

pp. 254-265 ◽

Cited By ~ 700

Author(s):

Peter Mercelis ◽

Jean‐Pierre Kruth

Keyword(s):

Residual Stresses ◽

Selective Laser Melting ◽

Selective Laser Sintering ◽

Laser Sintering ◽

Laser Melting

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A Method to Estimate Residual Stress in Metal Parts Made by Selective Laser Melting

Volume 2A: Advanced Manufacturing ◽

10.1115/imece2015-52386 ◽

2015 ◽

Cited By ~ 5

Author(s):

Xiaoqing Wang ◽

Y. Kevin Chou

Keyword(s):

Residual Stress ◽

Additive Manufacturing ◽

Residual Stresses ◽

Selective Laser Melting ◽

Inconel 718 ◽

Plane Surface ◽

Texture Evolution ◽

Large Temperature ◽

Indentation Hardness ◽

Laser Melting

Accurate evaluation of residual stresses in structures is very important because they play a crucial role in the mechanical performance of the components. As residual stresses can be introduced into mechanical components during various thermal or mechanical processes such as heat treatment, forming, welding and additive manufacturing. As an additive manufacturing method, selective laser melting (SLM) has become a powerful tool for the direct manufacturing of three dimensional nano-composite components with complex configurations directly from powders using 3D CAD data as a digital information source and energy in the form of a high-power laser beam. Therefore, the application of the SLM technology is necessary to manufacture Inconel 718 superalloy, which has been widely employed in industrial applications due to its remarkable properties. Hence, it is critical to measure and reduce the residual stress in the Inconel 718 parts formed by SLM due to rapid cooling and reheating. In this study, the process-induced residual stress in Inconel 718 parts produced by selective laser melting (SLM) has been investigated using the model established by Carlsson et al., which is an instrumented indentation technique based on the experimental correlation between the indentation characteristic and the residual stress. The samples were sectioned from an Inconel 718 block along its build direction, and subsequently prepared with general metallographic methods for Vickers indentation and measurements by optical microscopy. The residual stress on the scanning surface (Z-plane) and side surface (X-plane) at different build heights have been evaluated in micro-scale with the contact area, indentation hardness and the equai-biaxial residual stress and strain fields. The results show that the residual stress is unevenly distributed in the SLMed parts with some areas have an maximum absolute value around 350 MPa, about 30 percent of the yield strength of Inconel 718. The average residual stresses in the Z-plane and X-plane samples are tensile and compressive, respectively. Besides, the residual stress does not change significantly along the building direction of the part. Moreover, the Vickers hardness of the parts built with the SLM process is comparable to the literature, and the X-plane surface has a higher hardness than the Z-plane surface. The microstructures and texture evolution of the SLM processed Inconel 718 alloy are also investigated. The X-plane shows the columnar structure due to the large temperature gradient while the Z-plane presents the equiaxed structures. The random texture is shown in the SLM processed specimens.

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Utilização da técnica de difração de raios-X para o estudo de amostras de Ti-6Al-4V forjadas e fabricadas por fusão seletiva a laser

Ciência e Natura ◽

10.5902/2179460x35528 ◽

2019 ◽

Vol 40 ◽

pp. 249

Author(s):

Max Amorim Brum ◽

Fábio Beck ◽

Oreci Escobar da Silva ◽

Gustavo Luiz Callegari ◽

Marcos André Carara ◽

...

Keyword(s):

Residual Stresses ◽

Selective Laser Melting ◽

Structural Characteristics ◽

Lattice Parameter ◽

Manufacturing Processes ◽

X Ray Diffraction ◽

Laser Melting ◽

Engineering Project ◽

X Ray ◽

Great Relevance

The search for materials with well-defined characteristics is very important for any engineering project. In addition, it is known that the various types of manufacturing processes directly influence in properties of the parts. In this work, the X-ray diffraction technique was used to study the structural characteristics of Ti-6Al-4V samples manufactured by the forging and Selective Laser Melting techniques. We found that the samples made by FSL were able to present a reduction of 1% in the lattice parameter perpendicular to the studied plane, when compared with the forged samples. Since most of the parts manufactured by Selective Laser Melting meet the demands of aeronautical and aerospace projects, where residual stresses are generally undesirable for making the parts more fragile, studies like these acquire great relevance.

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