Selective Laser Melting of Pre-Alloyed NiTi Powder: Single-Track Study and FE Modeling with Heat Source Calibration

Unique functional properties such as the low stiffness, superelasticity, and biocompatibility of nickel–titanium shape-memory alloys provide many applications for such materials. Selective laser melting of NiTi enables low-cost customization of devices and the manufacturing of highly complex geometries without subsequent machining. However, the technology requires optimization of process parameters in order to guarantee high mass density and to avoid deterioration of functional properties. In this work, the melt pool geometry, surface morphology, formation mode, and thermal behavior were studied. Multiple combinations of laser power and scanning speed were used for single-track preparation from pre-alloyed NiTi powder on a nitinol substrate. The experimental results show the influence of laser power and scanning speed on the depth, width, and depth-to-width aspect ratio. Additionally, a transient 3D FE model was employed to predict thermal behavior in the melt pool for different regimes. In this paper, the coefficients for a volumetric double-ellipsoid heat source were calibrated with bound optimization by a quadratic approximation algorithm, the design of experiments technique, and experimentally obtained data. The results of the simulation reveal the necessary conditions of transition from conduction to keyhole mode welding. Finally, by combining experimental and FE modeling results, the optimal SLM process parameters were evaluated as P = 77 W, V = 400 mm/s, h = 70 μm, and t = 50 μm, without printing of 3D samples.

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Numerical Simulation of Moving Heat Flux during Selective Laser Melting of AlSi25 Alloy Powder

Metals ◽

10.3390/met10070877 ◽

2020 ◽

Vol 10 (7) ◽

pp. 877

Author(s):

Cong Ma ◽

Xianshun Wei ◽

Biao Yan ◽

Pengfei Yan

Keyword(s):

Numerical Simulation ◽

Selective Laser Melting ◽

Process Parameters ◽

Molten Pool ◽

Laser Power ◽

Scanning Speed ◽

Powder Layer ◽

Maximum Temperature ◽

Three Dimensional Model ◽

Laser Melting

A single-layer three-dimensional model was created to simulate multi-channel scanning of AlSi25 powder in selective laser melting (SLM) by the finite element method. Thermal behaviors of laser power and scanning speed in the procedure of SLM AlSi25 powder were studied. With the increase of laser power, the maximum temperature, size and cooling rate of the molten pool increase, while the scanning speed decreases. For an expected SLM process, a perfect molten pool can be generated using process parameters of laser power of 180 W and a scanning speed of 200 mm/s. The pool is greater than the width of the scanning interval, the depth of the molten pool is close to scan powder layer thickness, the temperature of the molten pool is higher than the melting point temperature of the powder and the parameters of the width and depth are the highest. To confirm the accuracy of the simulation results of forecasting excellent process parameters, the SLM experiment of forming AlSi25 powder was carried out. The surface morphology of the printed sample is intact without holes and defects, and a satisfactory metallurgical bond between adjacent scanning channels and adjacent scanning layers was achieved. Therefore, the development of numerical simulation in this paper provides an effective method to obtain the best process parameters, which can be used as a choice to further improve SLM process parameters. In the future, metallographic technology can also be implemented to obtain the width-to-depth ratio of the SLM sample molten pool, enhancing the connection between experiment and theory.

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A Study of Keyhole Porosity in Selective Laser Melting: Single-Track Scanning With Micro-CT Analysis

Journal of Manufacturing Science and Engineering ◽

10.1115/1.4043622 ◽

2019 ◽

Vol 141 (7) ◽

Cited By ~ 12

Author(s):

Subin Shrestha ◽

Thomas Starr ◽

Kevin Chou

Keyword(s):

Selective Laser Melting ◽

Laser Power ◽

Scanning Speed ◽

Single Track ◽

Micro Computed Tomography ◽

Laser Melting ◽

Pore Characteristics ◽

Line Energy ◽

The Individual ◽

Pore Number

Porosity is an inherent attribute in selective laser melting (SLM) and profoundly degrades the build part quality and its performance. This study attempts to understand and characterize the keyhole pores formed during single-track scanning in SLM. First, 24 single tracks were generated using different line energy density (LED) levels, ranging from 0.1 J/mm to 0.98 J/mm, by varying the laser power and the scanning speed. The samples were then scanned by micro-computed tomography to measure keyhole pores and analyze the pore characteristics. The results show a general trend that the severity of the keyhole porosity increases with the increase of the LED with exceptions of certain patterns, implying important individual contributions from the parameters. Next, by keeping the LED constant in another set of experiments, different combinations of the power and the speed were tested to investigate the individual effect. Based on the results obtained, the laser power appears to have a greater effect than the scanning speed on both the pore number and the pore volume as well as the pore depth. For the same LED, the pore number and volume increase with increasing laser power until a certain critical level, beyond which, both the pore number and volume will decrease, if the power is further increased. For the LED of 0.32 J/mm, 0.4 J/mm, and 0.48 J/mm, the critical laser power that reverses the trend is about 132 W, 140 W, and 144 W, respectively.

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A Sensitivity Analysis Study on the Material Properties and Process Parameters for Selective Laser Melting of Inconel 625

Volume 1: Processing ◽

10.1115/msec2015-9321 ◽

2015 ◽

Cited By ~ 2

Author(s):

Luis E. Criales ◽

Yiğit M. Arısoy ◽

Tuğrul Özel

Keyword(s):

Additive Manufacturing ◽

Selective Laser Melting ◽

Process Parameters ◽

Scanning Speed ◽

Inconel 625 ◽

Pool Data ◽

Temperature Profiles ◽

Laser Melting ◽

Melt Pool ◽

Laser Heat Source

A prediction of the 2-D temperature profile and melt pool geometry for Selective Laser Melting (SLM) of Inconel 625 metal powder with a numerically-based approach for solving the heat conduction-diffusion equation was established in this paper. A finite element method solution of the governing equation was developed. A review of the current efforts in numerical modeling for laser-based additive manufacturing is presented. Initially, two-dimensional (2-D) temperature profiles along the scanning (x-direction) and hatch direction (y-direction) are calculated for a moving laser heat source to understand the temperature rise due to heating during SLM. The effects of varying laser power, scanning speed and the powder material’s density are analyzed. Based on the predicted temperature distributions, melt pool geometry, i.e. the locations at which melting of the powder material occurs, is determined. The results are chiefly compared against the published literature on melt pool data. The main goal of this research is to develop a computational tool with which investigation of the importance of various laser, material, and process parameters on the built dimensional quality in laser-based additive manufacturing becomes not only possible but also practical and reproducible.

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Experimental Investigation into the Single-Track of Selective Laser Melting of IN625

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.233-235.2844 ◽

2011 ◽

Vol 233-235 ◽

pp. 2844-2848 ◽

Cited By ~ 11

Author(s):

Li Wang ◽

Qing Song Wei ◽

Yu Sheng Shi ◽

Jin Hui Liu ◽

Wen Ting He

Keyword(s):

Energy Density ◽

Relative Density ◽

Surface Quality ◽

Selective Laser Melting ◽

Laser Power ◽

Laser Energy ◽

Scanning Speed ◽

Single Track ◽

Laser Melting ◽

Metallic Parts

Selective laser melting(SLM) is driven by the need to fabricate functional metallic parts and tools with near shape and density. The method of process to fabricate a metal part will save materials, time and energy compared to the traditional manufacturing methods. Unlike the selective laser sintering (SLS), the metal powder particles are molten by the laser beam during the process of selective laser melting. In this paper, IN625 powders were adopted to investigate the characters of single molten track. The factors that affect the surface quality and relative density are the process parameters such as the laser energy, scan speed and so on. They were studied to find out the correlation between the parameters and formation of single-track. It has been found that Optimal ratio between laser power and scanning speed (P/v) is 1-1.5 for IN625 SLM. P/v is the linear energy density. It also has been found that the width and height of single-track can be calculated when the linear energy density is given. In this study the laser power, scan spacing and the hatch spacing which affect the surface quality and the relative density of the metallic parts were optimized.

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The Influence of Selective Laser Melting Process Parameters on the Property of TiAlN/TiN Multilayer Coating on the 316L Steel

Coatings ◽

10.3390/coatings9060377 ◽

2019 ◽

Vol 9 (6) ◽

pp. 377 ◽

Cited By ~ 2

Author(s):

Yueling Lyu ◽

Jingwei Wang ◽

Yulin Wan ◽

Yangzhi Chen

Keyword(s):

Selective Laser Melting ◽

Process Parameters ◽

Laser Power ◽

Orthogonal Experiment ◽

Multilayer Coating ◽

Melting Process ◽

Scanning Speed ◽

Laser Melting ◽

Wear Rates ◽

Comprehensive Property

Selective laser melting (SLM) is an important advanced additive manufacturing technology. The existing SLM products cannot fully meet the requirements of high-precision and strength of the mechanical component because of their defects. The TiAlN/TiN multilayer coating can improve the surface property of SLM products. The present work aims to explore the influences of different process parameters of SLM on the property of TiAlN/TiN multilayer coating plating on the 361L specimen and the mechanism of these influences. Taking laser power, scanning speed, and scanning space as factors, an orthogonal experiment was designed. The TiAlN/TiN multilayer coating specimens can be obtained by plating on the 361L specimen, fabricated by the process parameters of SLM on the orthogonal experiment. The surface topographies and properties of TiAlN/TiN multilayer coating were tested, the influences of SLM process parameters on TiAlN/TiN multilayer coating were analyzed, and the optimal process parameter was obtained. The electron microscope images revealed that the surface morphology of TiAlN/TiN multilayer coating plating on the SLM specimen was relatively flat, and there were some macro-particles in different sizes and pin holes dispersed on it. The thickness of the TiAlN/TiN multilayer coating was 2.77–3.29 μm. The microhardness value of coating SLM specimen was more than four times that of the uncoated SLM specimen and the wear rates of the uncoated specimen were 2–4 times that of the corresponding coating specimen. The comprehensive analysis shows that the laser power had the greatest influence on the comprehensive property of the coating. The primary cause of the influence of SLM process parameters on the properties of the TiAlN/TiN multilayer coating was preliminarily discussed. When the laser power was 170 W, the scanning speed was 1,100 mm/s, and the scanning space was 0.08mm, the TiAlN/TiN multilayer coating plating on the SLM specimen had the best comprehensive property.

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The Thermo-Mechanical Coupling Effect in Selective Laser Melting of Aluminum Alloy Powder

Materials ◽

10.3390/ma14071673 ◽

2021 ◽

Vol 14 (7) ◽

pp. 1673

Author(s):

Xianyin Duan ◽

Xinyue Chen ◽

Kunpeng Zhu ◽

Tao Long ◽

Shiyang Huang ◽

...

Keyword(s):

Aluminum Alloy ◽

Stress Distribution ◽

Heat Source ◽

Laser Power ◽

Alloy Powder ◽

Scanning Speed ◽

Laser Melting ◽

Spot Diameter ◽

Melt Pool ◽

Aluminum Alloy Powder

In the selective laser melting process, metal powder melted by the laser heat source generates large instantaneous energy, resulting in transient high temperature and complex stress distribution. Different temperature gradients and anisotropy finally determine the microstructure after melting and affect the build quality and mechanical properties as a result. It is important to monitor and investigate the temperature and stress distribution evolution. Due to the difficulties in online monitoring, finite element methods (FEM) are used to simulate and predict the building process in real time. In this paper, a thermo-mechanical coupled FEM model is developed to predict the thermal behaviors of the melt pool by using Gaussian moving heat source. The model could simulate the shapes of the melt pool, distributions of temperature and stress under different process parameters through FEM. The influences of scanning speed, laser power, and spot diameter on the distribution of the melt pool temperature and stress are investigated in the SLM process of Al6063, which is widely applied in aerospace, transportation, construction and other fields due to its good corrosion resistance, sufficient strength and excellent process performance. Based on transient analysis, the relationships are identified among these process parameters and the melt pool morphology, distribution of temperature and thermal stress. It is shown that the maximum temperature at the center point of the scanning tracks will gradually increase with the increment of laser power under the effect of thermal accumulation and heat conduction, as the preceded scanning will preheat the subsequent scanning tracks. It is recommended that the parameters with optimized laser power (P = 175–200 W), scanning speed (v = 200–300 mm/s) and spot diameter (D = 0.1–0.15 mm) of aluminum alloy powder can produce a high building quality of the SLM parts under the pre-set conditions.

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Edge and corner effects in selective laser melting of IN 625 alloy

Manufacturing Review ◽

10.1051/mfreview/2020008 ◽

2020 ◽

Vol 7 ◽

pp. 8 ◽

Cited By ~ 1

Author(s):

Gheorghe Matache ◽

Mihai Vladut ◽

Alexandru Paraschiv ◽

Raluca Mihaela Condruz

Keyword(s):

Selective Laser Melting ◽

Laser Power ◽

Scanning Speed ◽

Experimental Investigations ◽

Laser Melting ◽

Scanning Strategy ◽

Melt Pool ◽

Corner Effects ◽

Different Levels ◽

Surface Changes

Experimental investigations on top surface of prismatic specimens, manufactured by Selective Laser Melting of IN 625 alloy, were carried out in order to assess the influence of laser power and scanning speed on edge and corner effects. Since the melt-pool behaviour is strongly influenced by the process parameters, all specimens were manufactured with no contour using the same layer thickness, hatch distance and scanning strategy at different levels of laser powers and scanning speeds. 3D laser surface scanning was performed in order to measure surface changes. The experimental results have revealed that melt-pool behaviour during solidification generates elevated ridges on both specimen sides and corners that are strongly influenced by the energy input. The edge ridges width increases with increasing the laser power and decrease with increasing the scanning speed, the rising of corners being much more pronounced. On the contrary, at constant laser power and variable scanning speeds the edge and corner ridges decrease.

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Mechanical Properties of High-Strength Cu–Cr–Zr Alloy Fabricated by Selective Laser Melting

Materials ◽

10.3390/ma13215028 ◽

2020 ◽

Vol 13 (21) ◽

pp. 5028

Author(s):

Fujia Sun ◽

Ping Liu ◽

Xiaohong Chen ◽

Honglei Zhou ◽

Pengfei Guan ◽

...

Keyword(s):

Tensile Strength ◽

Selective Laser Melting ◽

Process Parameters ◽

Laser Power ◽

High Efficiency ◽

High Strength ◽

Scanning Speed ◽

Laser Melting ◽

Ansys Simulation ◽

Zr Alloy

The approximate process range for preparing the Cu–Cr–Zr alloy by selective laser melting (SLM) was determined by ANSYS simulation, and the influence of the SLM process parameters on the comprehensive properties of the SLM-formed alloy was studied by the design of experiments. The Cu–Cr–Zr alloy with optimum strength and hardness was prepared with high efficiency by optimizing the process parameters for SLM (i.e., laser power, scanning speed, and hatching distance). It is experimentally shown that tensile strength and hardness of the SLM alloy are increased by increasing laser power and decreasing scanning speed, whereas they are initially increased and then decreased by increasing the hatching distance. Moreover, strength, roughness and hardness of the SLM alloy are optimized when laser power is 460 W, scanning speed is 700 mm/s and hatching distance is 0.06 mm. The optimized properties of the SLM alloy are a tensile strength of 153.5 MPa, hardness of 119 HV, roughness of 31.384 μm and relative density of 91.62%.

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Effect of Process Parameters and Layer Thickness on the Quality and Performance of Ti-6Al-4V Fabricated by Selective Laser Melting

Coatings ◽

10.3390/coatings11111323 ◽

2021 ◽

Vol 11 (11) ◽

pp. 1323

Author(s):

Yanlong Jing ◽

Peng Wang ◽

Xiaoling Yan

Keyword(s):

Surface Quality ◽

Selective Laser Melting ◽

Exposure Time ◽

Process Parameters ◽

Laser Power ◽

Single Track ◽

Laser Melting ◽

Powder Bed ◽

Point Distance

To improve the quality of thick powder bed and realize the matching of thick powder bed and thin powder bed in the later stage, the influence of process parameters for the single-track, multi-layer fabrication, relative density, surface quality, defect, remelting, and boundary optimization performance of different layer thicknesses of Ti-6Al-4V fabricated by selective laser melting were investigated. It is more conducive to the stable forming of single-track when the point distance is half the diameter of the laser beam, and the exposure time is appropriately extended. The thin powder bed needs the corresponding point distance and exposure time under the laser power of 280–380 W to obtain high-density specimens. The thick powder bed needs to be able to ensure the formation of high-quality specimens under the smaller point distance and longer exposure time under higher laser power of 380 W. Both thick powder bed and thin powder bed will cause un-melted defects between molten pools, spheroidization defects caused by splashing, and microporous defects. The remelting process can significantly improve the surface quality of the formed specimen, but the surface quality of the thick powder bed is worse than that of the thin powder bed. The boundary quality of thick powder bed is worse than that of thin powder bed, and the boundary shape has a greater influence on the quality of the SLM forming boundary. Different strategies should be adopted to form the boundary of different shapes. Increasing the boundary count and increasing the laser power are more conducive to the improvement of boundary quality.

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