Fundamentals of radiation heat transfer in AlSi10Mg powder bed during selective laser melting

2019 ◽  
Vol 25 (9) ◽  
pp. 1506-1515 ◽  
Author(s):  
Pei Wei ◽  
Zhengying Wei ◽  
Zhne Chen ◽  
Jun Du ◽  
Yuyang He ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Energy Density ◽  
Negative Impact ◽  
Laser Energy ◽  
Melting Process ◽  
Laser Energy Density ◽  
Granular System ◽  
Laser Melting ◽  
Content Type ◽  
Powder Bed

Purpose This paper aims to study numerically the influence of the applied laser energy density and the porosity of the powder bed on the thermal behavior of the melt and the resultant instability of the liquid track. Design/methodology/approach A three-dimensional model was proposed to predict local powder melting process. The model accounts for heat transfer, melting, solidification and evaporation in granular system at particle scale. The proposed model has been proved to be a good approach for the simulation of the laser melting process. Findings The results shows that the applied laser energy density has a significantly influence on the shape of the molten pool and the local thermal properties. The relative low or high input laser energy density has the main negative impact on the stability of the scan track. Decreasing the porosity of the powder bed lowers the heat dissipation in the downward direction, resulting in a shallower melt pool, whereas pushing results in improvement in liquid track quality. Originality/value The randomly packed powder bed is calculated using discrete element method. The powder particle information including particle size distribution and packing density is taken into account in placement of individual particles. The effect of volumetric shrinkage and evaporation is considered in numerical model.

Theoretical and experimental study on surface roughness of 316L stainless steel metal parts obtained through selective laser melting

2016 ◽  
Vol 22 (4) ◽  
pp. 706-716 ◽  
Author(s):  
Di Wang ◽  
Yang Liu ◽  
Yongqiang Yang ◽  
Dongming Xiao
Keyword(s):  
Surface Roughness ◽  
Energy Density ◽  
Surface Quality ◽  
Theoretical Foundation ◽  
Laser Energy ◽  
Melting Zone ◽  
Laser Energy Density ◽  
Single Track ◽  
Laser Melting ◽  
Content Type

Purpose The purpose of this paper is to provide a theoretical foundation for improving the selective laser melting (SLM) surface roughness. To improve the part’s surface quality during SLM process, the upper surface roughness of SLM parts was theoretically studied and the influencing factors were analyzed through experiments. Design/methodology/approach The characteristics of single track were first investigated, and based on the analysis of single track, theoretical value of the upper surface roughness would be calculated. Two groups of cubic sample were fabricated to validate SLM parts’ surface roughness, the Ra and relative density of all the cubic parts was measured, and the difference between theoretical calculation and experiment results was studied. Then, the effect of laser energy density on surface roughness was studied. At last, the SLM part’s surface was improved by laser re-melting method. At the end of this paper, the curved surface roughness was discussed briefly. Findings The SLM upper surface roughness is affected by the width of track, scan space and the thickness of powder layer. Measured surface roughness Ra value was about 50 per cent greater than the theoretical value. The laser energy density has a great influence on the SLM fabrication quality. Different laser energy density corresponds to different fabricating characteristics. This study divided the SLM fabrication into not completely melting zone, balling zone in low energy density, successfully fabricating zone and excessive melting zone. The laser surface re-melting (LSR) process can improve the surface roughness of SLM parts greatly without considering the fabricating time and stress accumulation. Originality/value The upper surface roughness of SLM parts was theoretically studied, and the influencing factors were analyzed together; also, the LSR process was proven to be effective to improve the surface quality. This study provides a theoretical foundation to improve the surface quality of SLM parts to promote the popularization and application of metal additive manufacturing technology.

scholarly journals Machinability of INCONEL718 Alloy with a Porous Microstructure Produced by Laser Melting Powder Bed Fusion at Higher Energy Densities

Materials ◽  
2020 ◽  
Vol 13 (24) ◽  
pp. 5730
Author(s):  
Paul Wood ◽  
Antonio Díaz-Álvarez ◽  
José Díaz-Álvarez ◽  
María Henar Miguélez ◽  
Alexis Rusinek ◽  
...  
Keyword(s):  
Energy Density ◽  
Laser Energy ◽  
Cutting Speed ◽  
Machining Process ◽  
Laser Energy Density ◽  
Powder Bed Fusion ◽  
Laser Melting ◽  
Powder Bed ◽  
Orthogonal Turning ◽  
Different Levels

Products produced by additive manufacturing (AM) seek to exploit net shape manufacturing by eliminating or minimizing post-process stages such as machining. However, many applications which include turbo machinery components with tight dimensional tolerances and a smooth surface finish will require at least a light machine finishing stage. This paper investigates the machinability of the additively fabricated INCONEL718 (IN718) alloy produced by laser melting powder bed fusion (LM-PBF) with different levels of spherical porosity in the microstructure. The literature suggests that the band width for laser energy density, which combines the various scan process parameters to obtain a low spherical type porosity in the LM-PBF IN718 alloy (~1%), has wide breadth. With the increasing laser energy density and above a threshold, there is a rapid increase in the spherical pore size. In this paper, three tube samples each with different levels of spherical porosity were fabricated by varying the laser energy density for LM-PBF of the IN718 alloy within the stable and higher energy density range and the porosity measured. A low laser energy density was avoided due to balling up, which promotes highly irregular lack of fusion defects and poor consolidation within the alloy microstructure. An orthogonal turning test instrumented, with a three-component dynamometer to measure the cutting forces, was performed on AM produced IN718 tube samples under light cut conditions to simulate a finish machining process. The orthogonal turning tests were also performed on a tube sample obtained from the wrought extruded stock. The machining process parameters, which were studied include varying the cutting speed at three levels, at a fixed feed and under dry cut conditions for a short duration to avoid the tool wear. The results obtained were discussed and a notable finding was the higher rate of built-up-edge formation on the tool tip from the AM samples with a higher porosity and especially at a higher cutting speed. The paper also discusses the mechanisms that underpin the findings.

Inhibition of phase transformation from β- to α-tricalcium phosphate with addition of poly (L-lactic acid) in selective laser sintering

2014 ◽  
Vol 20 (5) ◽  
pp. 369-376 ◽  
Author(s):  
Cijun Shuai ◽  
Jingyu Zhuang ◽  
Shuping Peng ◽  
Xuejun Wen
Keyword(s):  
Phase Transformation ◽  
Lactic Acid ◽  
Liquid Phase ◽  
Energy Density ◽  
Porous Structure ◽  
Laser Energy ◽  
Selective Laser Sintering ◽  
Transient Liquid Phase ◽  
Laser Energy Density ◽  
Content Type

Purpose – The paper aims to fabricate an α-tricalcium phosphate (TCP) scaffold with an interconnected porous structure via selective laser sintering (SLS). To inhibit the phase transformation from β- to α-TCP in fabrication process of porous scaffolds, a small amount (1 weight per cent) of poly (L-lactic acid) (PLLA) is added into β-TCP powder to introduce the transient liquid phase. Design/methodology/approach – The paper opted for the transient liquid phase of melting PLLA to decrease the sintering temperature in SLS. Meanwhile, the densification of β-TCP is enhanced with a combined effect of the capillary force caused by melting PLLA and the surface energy of β-TCP particles. Moreover, the PLLA will gradually decompose and completely disappear with laser irradiation. Findings – The testing results show the addition of PLLA enables the scaffolds to achieve a higher β-TCP content of 77 ± 1.49 weight per cent compared with the scaffold sintered from β-TCP powder (60 ± 1.65 weight per cent), when the laser energy density is 0.4 J/mm2. The paper provides the mechanism of PLLA inhibition on the phase transformation from β- to α-TCP. And the optimum sintering parameters are obtained based on experimental results, which are used to prepare a TCP scaffold with an interconnected porous structure via SLS. Research limitations/implications – This paper shows that the laser energy density is an important sintering parameter that can provide the means to control the micro-porous structure of the scaffold. If the laser energy density is too low, the densification is not enough. On the other hand, if the laser energy density is too high, the microcracks are observed which are attributed to the volume expansion during the phase transformation from β- to α-TCP. Therefore, the laser energy density must be optimized. Originality/value – The paper provides a feasible method for fabricating TCP artificial bone scaffold with good biological and mechanical properties.

Optimization of parameters for SLS of WC-Co

2017 ◽  
Vol 23 (6) ◽  
pp. 1202-1211 ◽  
Author(s):  
Sanjay Kumar ◽  
Aleksander Czekanski
Keyword(s):  
Energy Density ◽  
Process Parameters ◽  
Laser Power ◽  
Laser Energy ◽  
Beam Diameter ◽  
Content Type ◽  
Powder Bed ◽  
Scan Speed ◽  
New Equation ◽  
Hatch Spacing

Purpose WC-Co is a well-known material for conventional tooling but is not yet commercially available for additive manufacturing. Processing it by selective laser sintering (SLS) will pave the way for its commercialization and adoption. Design/methodology/approach It is intended to optimize process parameters (laser power, hatch spacing, scan speed) by fabricating a bigger part (minimum size of 10 mm diameter and 5 mm height). Microstructural analysis, EDX and hardness testing is used to study effects of process parameters. Optimized parameter is ascertained after fabricating 49 samples in preliminary experiment, 27 samples in pre-final experiment and 9 samples in final experiment. Findings Higher laser power gives rise to cracks and depletion of cobalt while higher scan speed increases porosity. Higher hatch spacing is responsible for delamination and displacement of parts. Optimized parameters are 270 W laser power, 500 mm/s scan speed, 0.04 mm layer thickness, 0.04 mm hatch spacing (resulting in energy density of 216 J/mm3) and 200°C powder bed temperature. A part comprising of small hole of 2 mm diameter, thin cylindrical pin of 0.5 mm diameter and thin wall of 2 mm width bent up to 30° angle to the base plate is fabricated. In order to calculate laser energy density, a new equation is introduced which takes into account both beam diameter and hatch spacing unlike old equation does. In order to calculate laser energy density, a new equation is formulated which takes into account both beam diameter and hatch spacing unlike old equation does. WC was not completely melted as intended giving rise to partial melting-type binding mechanism. This justified the name SLS for process in place of SLM (Selective Laser Melting). Research limitations/implications Using all possible combination of parameters plus heating the part bed to maximum shows limitation of state-of-the-art commercial powder bed fusion machine for shaping hardmetal consisting of high amount of WC (83 wt. per cent). Practical implications The research shows that microfeatures could be fabricated using WC-Co which will herald renewed interest in investigating hardmetals using SLS for manufacturing complex hard tools, molds and wear-resistance parts. Originality/value This is the first time micro features are successfully fabricated using WC-Co without post-processing (infiltration, machining) and without the help of additional binding material (such as Cu, Ni, Fe).

Study on the selective laser sintering of a low-isotacticity polypropylene powder

2016 ◽  
Vol 22 (4) ◽  
pp. 621-629 ◽  
Author(s):  
Wei Zhu ◽  
Chunze Yan ◽  
Yunsong Shi ◽  
Shifeng Wen ◽  
Changjun Han ◽  
...  
Keyword(s):  
Particle Size ◽  
Tensile Strength ◽  
Energy Density ◽  
Laser Energy ◽  
Selective Laser Sintering ◽  
Laser Energy Density ◽  
Content Type ◽  
Crystalline Polymers ◽  
Polyamide 12 ◽  
Degradation Temperature

Purpose Semi-crystalline polymers such as polyamide-12 can be used for selective laser sintering (SLS) to make near-fully dense plastic parts. At present, however, the types of semi-crystalline polymers suitable for SLS are critically limited. Therefore, the purpose of this paper is to investigate the processibility of a new kind of semi-crystalline polypropylene (PP) with low isotacticity for SLS process. Design/methodology/approach The SLS processibility of the PP powder, including particle size and shape, sintering window, degree of crystallinity and degradation temperature, was evaluated. Effects of the applied laser energy density on the surface micromorphology, density, tensile strength and thermal properties of SLS-built PP specimens were studied. Findings The results show that the PP powder has a nearly spherical shape, smooth surfaces, an appropriate average particle size of 63.6 μm, a broad sintering window of 21 oC and low crystalline degree of 30.4 per cent comparable to that of polyamide-12, a high degradation temperature of 381.8°C and low part bed temperature of 105°C, indicating a very good SLS processibility. The density and the tensile strength first increase with increasing laser energy density until they reach the maximum values of 0.831 g/cm3 and 19.9 MPa, respectively, at the laser energy density of 0.0458 J/mm2, and then decrease when the applied laser energy density continue to increase owing to the degradation of PP powders. The complex PP components have been manufactured by SLS using the optimum parameters, which are strong enough to be directly used as functional parts. Originality/value This paper provides a new knowledge for this field that low-isotacticity PPs exhibit good SLS processibility, therefore increasing material types and broadening the application of SLS technology.

Selective Laser Melting Additive Manufacturing of Novel Aluminum Based Composites With Multiple Reinforcing Phases

2015 ◽  
Vol 137 (2) ◽  
Author(s):  
Dongdong Gu ◽  
Fei Chang ◽  
Donghua Dai
Keyword(s):  
Mechanical Properties ◽  
Additive Manufacturing ◽  
Energy Density ◽  
Selective Laser Melting ◽  
Laser Energy ◽  
Laser Energy Density ◽  
Wear Property ◽  
Laser Melting ◽  
Sic Particles

The selective laser melting (SLM), due to its unique additive manufacturing (AM) processing manner and laser-induced nonequilibrium rapid melting/solidification mechanism, has a promising potential in developing new metallic materials with tailored performance. In this work, SLM of the SiC/AlSi10Mg composites was performed to prepare the Al-based composites with the multiple reinforcing phases. The influence of the SLM processing parameters on the constitutional phases, microstructural features, and mechanical performance (e.g., densification, microhardness, and wear property) of the SLM-processed Al-based composites was studied. The reinforcing phases in the SLM-processed Al-based composites included the unmelted micron-sized SiC particles, the in situ formed micron-sized Al4SiC4 strips, and the in situ produced submicron Al4SiC4 particles. As the input laser energy density increased, the extent of the in situ reaction between the SiC particles and the Al matrix increased, resulting in the larger degree of the formation of Al4SiC4 reinforcement. The densification rate of the SLM-processed Al-based composite parts increased as the applied laser energy density increased. The sufficiently high density (∼96% theoretical density (TD)) was achieved for the laser linear energy density larger than 1000 J/m. Due to the generation of the multiple reinforcing phases, the elevated mechanical properties were obtained for the SLM-processed Al-based composites, showing a high microhardness of 214 HV0.1, a considerably low coefficient of friction (COF) of 0.39, and a reduced wear rate of 1.56 × 10−5 mm3 N−1 m−1. At an excessive laser energy input, the grain size of the in situ formed Al4SiC4 reinforcing phase, both the strip- and particle-structured Al4SiC4, increased markedly. The significant grain coarsening and the formation of the interfacial microscopic shrinkage porosity lowered the mechanical properties of the SLM-processed Al-based composites. These findings in the present work are applicable and/or transferrable to other laser-based powder processing processes, e.g., laser cladding, laser metal deposition, or laser engineered net shaping.

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