Stress and Deformation Evaluations of Scanning Strategy Effect in Selective Laser Melting

2016 ◽  
Author(s):  
Bo Cheng ◽  
Subin Shrestha ◽  
Y. Kevin Chou
Keyword(s):  
Residual Stresses ◽  
Laser Beam ◽  
Selective Laser Melting ◽  
High Energy ◽  
Powder Layer ◽  
Stress Difference ◽  
Laser Melting ◽  
Scanning Strategy ◽  
Scanning Pattern ◽  
Stress And Deformation

Selective laser melting (SLM) is one of the Additive manufacturing (AM) processes that can build physical part in an added material method from digital data. In such a process, computer designed part model will be decomposed into hundreds of thousands of layers. The layered information is then transferred to SLM equipment and the part is built in a layer by layer fashion. Each powder layer will be scanned and melted in the required region by a high energy laser beam in a given scanning pattern so as to form a desired geometry. Finally, fully functional parts can be produced by repeatedly powder deposition, melting and solidification process. This process offers numerous advantages such as tooling-free productions and design freedom in geometry. In addition, SLM process is quite suitable for complicated parts such as customer designed medical implants and internal channels which are difficult to manufacture by conventional methods such as casting and machining. However, the localized heating and cooling process can lead to defects such as high residual stress, part distortion or delamination failure in SLM fabricated parts. These potential defects may impede the wide application of this technology. It is known that the laser beam scanning path will affect the thermomechanical behaviors of the build part, and thus, altering the scanning pattern may be a feasible strategy to reduce residual stresses and deformations by influencing the heat intensity input distribution. In this study, a 3D sequentially coupled finite element method (FEM) model, incorporating a volumetric moving Gaussian heat source, powder as well as solid material temperature dependent properties and layer addition features, was developed to study the complex thermomechanical process of SLM. The model was applied to evaluate six different scanning strategies effect on part temperature, stress and deformation. The major results have been summarized as follows. (1) Among all cases tested, the out-in scanning pattern has the maximum stresses along the X and Y directions; while the 45 degree inclined scanning may reduce residual stresses in both directions. (2) Large directional stress difference can be caused by back and forth line scanning strategy while minor directional stress difference is observed for other tested cases. (3) X and Y directional stress concentration is shown around the edge of deposited layers and the interface between deposited layers and substrate for all cases. (4) The 45 degree inclined scanning case has the smallest build direction deformation while the in-out scanning case has the largest deformation among the tested cases.

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

Materials ◽  
2018 ◽  
Vol 11 (10) ◽  
pp. 1821 ◽  
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.

Investigation of Sectoral Scanning in Selective Laser Melting

2010 ◽  
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.

scholarly journals Uncertainties Induced by Processing Parameter Variation in Selective Laser Melting of Ti6Al4V Revealed by In-Situ X-ray Imaging

Materials ◽  
2022 ◽  
Vol 15 (2) ◽  
pp. 530
Author(s):  
Zachary A. Young ◽  
Meelap M. Coday ◽  
Qilin Guo ◽  
Minglei Qu ◽  
S. Mohammad H. Hojjatzadeh ◽  
...  
Keyword(s):  
Laser Beam ◽  
Selective Laser Melting ◽  
Small Deviation ◽  
Processing Parameters ◽  
Powder Layer ◽  
Beam Size ◽  
Processing Parameter ◽  
Laser Melting ◽  
Melt Pool

Selective laser melting (SLM) additive manufacturing (AM) exhibits uncertainties, where variations in build quality are present despite utilizing the same optimized processing parameters. In this work, we identify the sources of uncertainty in SLM process by in-situ characterization of SLM dynamics induced by small variations in processing parameters. We show that variations in the laser beam size, laser power, laser scan speed, and powder layer thickness result in significant variations in the depression zone, melt pool, and spatter behavior. On average, a small deviation of only ~5% from the optimized/reference laser processing parameter resulted in a ~10% or greater change in the depression zone and melt pool geometries. For spatter dynamics, small variation (10 μm, 11%) of the laser beam size could lead to over 40% change in the overall volume of the spatter generated. The responses of the SLM dynamics to small variations of processing parameters revealed in this work are useful for understanding the process uncertainties in the SLM process.

Model of Radiation and Heat Transfer in Laser-Powder Interaction Zone at Selective Laser Melting

2009 ◽  
Vol 131 (7) ◽  
Author(s):  
A. V. Gusarov ◽  
I. Yadroitsev ◽  
Ph. Bertrand ◽  
I. Smurov
Keyword(s):  
Laser Beam ◽  
Selective Laser Melting ◽  
Metallic Powder ◽  
Single Line ◽  
Powder Layer ◽  
Width Ratio ◽  
Beam Diameter ◽  
Laser Melting ◽  
Scanning Velocity ◽  
Melt Pool

A model for coupled radiation transfer and thermal diffusion is proposed, which provides a local temperature field. Single-line scanning of a laser beam over a thin layer of metallic powder placed on a dense substrate of the same material is studied. Both the laser beam diameter and the layer thickness are about 50 μm. The typical scanning velocity is in the range of 10–20 cm/s. An effective volumetric heat source is estimated from laser radiation scattering and absorption in a powder layer. A strong difference in thermal conductivity between the powder bed and dense material is taken into account. The above conditions correspond to the technology of selective laser melting that is applied to build objects of complicated shape from metallic powder. Complete remelting of the powder in the scanned zone and its good adhesion to the substrate ensure fabrication of functional parts with mechanical properties close to the ones of the wrought material. Experiments with single-line melting indicate that an interval of scanning velocities exists, where the remelted tracks are uniform. The tracks become “broken” if the scanning velocity is outside this interval. This is extremely undesirable and referred to as the “balling” effect. The size and the shape of the melt pool and the surface of the metallurgical contact of the remelted material to the substrate are analyzed in relation to the scanning velocity. The modeling results are compared with experimental observation of laser tracks. The experimentally found balling effect at scanning velocities above ∼20 cm/s can be explained by the Plateau–Rayleigh capillary instability of the melt pool. Two factors destabilize the process with increasing the scanning velocity: increasing the length-to-width ratio of the melt pool and decreasing the width of its contact with the substrate.

Analytical Solution of Temperature Distribution in a Nonuniform Medium Due to a Moving Laser Beam and a Double Beam Scanning Strategy in the Selective Laser Melting Process

2018 ◽  
Vol 140 (8) ◽  
Author(s):  
Loong-Ee Loh ◽  
Jie Song ◽  
Fenglin Guo ◽  
Guijun Bi
Keyword(s):  
Temperature Distribution ◽  
Analytical Solution ◽  
Laser Beam ◽  
Selective Laser Melting ◽  
Melting Process ◽  
Laser Melting ◽  
Scanning Strategy ◽  
Beam Scanning ◽  
Double Beam ◽  
Scanning Strategies

Selective laser melting (SLM) has received increasing attention in recent years as an innovative manufacturing technique. The present SLM process only uses a single laser beam to melt and consolidate the powder, which may result in excessive evaporation. In this paper, a double beam scanning strategy is investigated in which the first laser beam preheats the powder just below the sintering point while the second laser beam completely melts the powder. An analytical solution on the temperature distribution heated by a moving laser beam in the powder-bulk domain is derived and is used to determine the critical radius of the first laser beam. The single and double beam scanning strategies are compared numerically and it is found that double beam scanning can effectively reduce material evaporation and increase the amount of powder melted in the SLM process.

scholarly journals Investigation of Performance and Residual Stress Generation of AlSi10Mg Processed by Selective Laser Melting

2018 ◽  
Vol 2018 ◽  
pp. 1-12 ◽  
Author(s):  
Lianfeng Wang ◽  
Xiaohui Jiang ◽  
Yihong Zhu ◽  
Zishan Ding ◽  
Xiaogang Zhu ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Residual Stress ◽  
Residual Stresses ◽  
Selective Laser Melting ◽  
Tilt Angle ◽  
Side Surface ◽  
Stress Generation ◽  
Laser Melting ◽  
Scanning Strategy ◽  
Preheating Temperature

During the selective laser melting (SLM) process, the scanned layers are subjected to rapid thermal cycles. By working on the mechanical properties, residual stress, and microstructure, the high-temperature gradients can have significant effect on the proper functioning and the structural integrity of built parts. This work presents a comprehensive study on the scanning path type and preheating temperature for AlSi10Mg alloy during SLM. According to the results, SLM AlSi10Mg parts fabricated in chessboard scanning strategy have higher mechanical properties or at least comparable to the parts fabricated in uniformity scanning strategy. In the SLM processing, the residual stress in different parts of the specimen varies with temperature gradient, and the residual stress at the edge of the specimen is obviously larger than that at the center. Under the chessboard scanning and preheating temperature 160°C, the residual stress in each direction of the specimens reaches the minimum. Under different forming processes, the morphology of the microstructure is obviously different. With the increase of preheating temperature, the molten pool in the side surface is obviously elongated and highly unevenly distributed. From the coupling relationship between the residual stress and microstructure, it can be found that the microstructure of top surface is affected by residual stresses σx and σy. But the side surface is mainly governed by residual stress σy; moreover, the greater the residual stress, the more obvious the grain tilt. In the XY and XZ surfaces, the scanning strategy has little influence on the tilt angle of the grain. But, the tilt angle and morphology of the microstructure are obviously affected by the preheating temperature. The results show that the residual stresses can effectively change the properties of the materials under the combined influence of scanning strategy and preheating temperature.

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