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

Additive manufacturing is a form of powder metallurgy, which means the properties of the initial metal powders (chemical composition, powder morphology and size) impact the final properties of the resulting parts. A complete characterization, including thermodynamic effects and the behavior of the metal powders at elevated temperatures, is crucial when planning the manufacturing process. The analysis of the Fe-Mn and Fe-Mn-Ag powder mixtures, made from pure elemental powders, shows a high susceptibility to sintering in the temperature interval from 700 to 1000 °C. Here, numerous changes to the manganese oxides and the αMn to βMn transformation occurred. The problems of mechanically mixed powders, when using selective laser melting, were highlighted by the low flowability, which led to a less controllable process, an uncontrolled arrangement of the powder and a large percentage of burnt manganese. All this was determined from the altered chemical compositions of the produced parts. The impact of the increased manganese content on the decreased probability of the transformation from γ-austenite to ε-martensite was confirmed. The ε-martensite in the microstructure increased the hardness of the material, but at the same time, its magnetic properties reduce the usefulness for medical applications. However, the produced parts had comparable elongations to human bone.

Download Full-text

Deformations and stresses prediction of cantilever structures fabricated by selective laser melting process

Rapid Prototyping Journal ◽

10.1108/rpj-10-2019-0273 ◽

2021 ◽

Vol 27 (3) ◽

pp. 453-464

Author(s):

Lan Li ◽

Tan Pan ◽

Xinchang Zhang ◽

Yitao Chen ◽

Wenyuan Cui ◽

...

Keyword(s):

Residual Stress ◽

Residual Stresses ◽

Selective Laser Melting ◽

Thermal Distortion ◽

Cantilever Beams ◽

Support Structures ◽

Laser Melting ◽

Content Type ◽

Two Samples ◽

Validation Experiments

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.

Download Full-text

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.

Download Full-text

Numerical modelling of the impact of energy distribution and Marangoni surface tension on track shape in selective laser melting of ceramic material

Additive Manufacturing ◽

10.1016/j.addma.2018.03.003 ◽

2018 ◽

Vol 21 ◽

pp. 713-723 ◽

Cited By ~ 13

Author(s):

Qiang Chen ◽

Gildas Guillemot ◽

Charles-André Gandin ◽

Michel Bellet

Keyword(s):

Surface Tension ◽

Numerical Modelling ◽

Energy Distribution ◽

Ceramic Material ◽

Selective Laser Melting ◽

Laser Melting ◽

The Impact

Download Full-text

Influence of Scanning Strategies on Processing of Aluminum Alloy EN AW 2618 Using Selective Laser Melting

Materials ◽

10.3390/ma11020298 ◽

2018 ◽

Vol 11 (2) ◽

pp. 298 ◽

Cited By ~ 32

Author(s):

Daniel Koutny ◽

David Palousek ◽

Libor Pantelejev ◽

Christian Hoeller ◽

Rudolf Pichler ◽

...

Keyword(s):

Aluminum Alloy ◽

Selective Laser Melting ◽

Laser Melting ◽

Scanning Strategies

Download Full-text

Influence of Abrasive Materials in Fluidised Bed Machining of AlSi10Mg Parts Made through Selective Laser Melting Technology

Key Engineering Materials ◽

10.4028/www.scientific.net/kem.813.129 ◽

2019 ◽

Vol 813 ◽

pp. 129-134 ◽

Cited By ~ 2

Author(s):

Andrea El Hassanin ◽

Maurizio Troiano ◽

Alessia Teresa Silvestri ◽

Vincenzo Contaldi ◽

Fabio Scherillo ◽

...

Keyword(s):

Surface Roughness ◽

Selective Laser Melting ◽

Impact Angle ◽

Fluidised Bed ◽

Laser Melting ◽

Abrasive Material ◽

Melting Technology ◽

Post Process ◽

The Impact ◽

Complex Parts

Metal Additive Manufacturing technologies development is increasing in a remarkable way due to their great potential concerning the production of complex parts with tailored characteristics in terms of design, material properties, usage and applications. Among all, the most widespread technologies are the Powder Bed Fusion based technologies such as Selective Laser Melting and Electron Beam Melting. However, the high surface roughness of the as-built parts still represents one of the major limitations, making necessary the adoption of post-process finishing to match the technological requirements for most of the fields of application. In this scenario, Fluidised Bed Machining represents an emerging finishing technology that could overcome some of the limitations of the most common methods, especially in terms of feasibility for the treatment of complex parts thanks to the fluid-like mobility of the abrasive material. This work deals with the preliminary tests of the Fluidised Bed Machining of additive manufactured samples using alumina as the abrasive material, investigating the effects of a high abrasive/substrate hardness ratio condition. The experiments were carried out on small plates of AlSi10Mg alloy made through Selective Laser Melting technology, built in the vertical direction with respect to the building plate. The influence of the impact angle and treatment time were investigated under bubbling fluidization conditions. Surface morphology evaluations were carried out pre and post process by means of Confocal Microscopy and Scanning Electron Microscopy (SEM). Weight loss measurements were conducted to evaluate the material removal rates as well. Results show a small influence of the specific impact angle, a slight reduction of the surface roughness and an asymmetrical effect of treatment, acting mostly on the sintered powders forming the peaks of the as-built surface.

Download Full-text

The Effect of a Scanning Strategy on the Residual Stress of 316L Steel Parts Fabricated by Selective Laser Melting (SLM)

Materials ◽

10.3390/ma11101821 ◽

2018 ◽

Vol 11 (10) ◽

pp. 1821 ◽

Cited By ~ 13

Author(s):

Di Wang ◽

Shibiao Wu ◽

Yongqiang Yang ◽

Wenhao Dou ◽

Shishi Deng ◽

...

Keyword(s):

Residual Stress ◽

Selective Laser Melting ◽

Laser Scanning ◽

Effective Means ◽

Laser Melting ◽

Scanning Strategy ◽

Deformation Degree ◽

316L Steel ◽

Stress And Deformation ◽

Scanning Strategies

The laser scanning strategy has an important influence on the surface quality, residual stress, and deformation of the molten metal (deformation behavior). A divisional scanning strategy is an effective means used to reduce the internal stress of the selective laser melting (SLM) metal part. In order to understand and optimize the divisional scanning strategy, three divisional scanning strategies and an S-shaped orthogonal scanning strategy are used to produce 316L steel parts in this study. The influence of scanning strategy on the produced parts is verified from the aspects of densification, residual stress distribution and deformation. Experiments show that the 316L steel alloy parts adopted spiral divisional scanning strategy can not only obtain the densification of 99.37%, but they also effectively improve the distribution of residual stress and control the deformation degree of the produced parts. Among them, the spiral divisional scanning sample has the smallest residual stress in plane direction, and its σx and σy stress are controlled within 204 MPa and 103 MPa. The above results show that the spiral divisional scanning is the most conducive strategy to obtain higher residual stress performance of SLM 316L steel parts.

Download Full-text

Thermal Modeling of 304L Stainless Steel for Selective Laser Melting: Laser Power Input Evaluation

Volume 2: Advanced Manufacturing ◽

10.1115/imece2017-72224 ◽

2017 ◽

Cited By ~ 4

Author(s):

Diego Augusto de Moraes ◽

Aleksander Czekanski

Keyword(s):

Stainless Steel ◽

Temperature Distribution ◽

Selective Laser Melting ◽

Laser Power ◽

Laser Scanning ◽

Power Input ◽

304L Stainless Steel ◽

Laser Melting ◽

Powder Bed ◽

The Impact

Selective Laser Melting (SLM) process is a Powder Bed Fusion (PBF) technique, which has shown significantly growth in the recent years. The demand for this process is justified by the versatility and ease in manufacturing the parts from 3D models as well for the increased complexity of engineered parts generated from topology or shape optimization. Automotive, aerospace, medical and aviation industries are taking great advantage of this process due the unique geometry characteristics found in the components. To enhance the benefits of SLM, a vital task is to analyze the laser power input impact on the temperature distribution through the powder bed, important for posterior residual stresses analysis. The Finite Element Method proposed in this study is a transient thermal model, able to predict temperature distribution through different sections of the powder bed when performing a single track of the laser scanning. Furthermore, the impact of the laser power input is carried out utilizing SS 304L, a low cost Stainless Steel alloy that can be employed in the SLM process, in order to determine the influence on the temperature distribution along the different cross sections.

Download Full-text