Porosity formation and gas bubble retention in laser metal deposition

Ng, Gary; Jarfors, Anders E. W.; Bi, Guijun; Zheng, Hong

doi:10.1007/s00339-009-5266-3

Cited by 172 publications

(92 citation statements)

References 15 publications

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“…The amount of powder delivered due to scanning speed will affect the quality of the part similar to changing the powder feed rate. The laser energy will affect the quality of a part as more melting helps to reduce porosity due to incomplete fusion, whereas too much energy can create entrapped gases in the melted zone (Ng et al, 2009). One powder will be used and the processing parameters optimised for this powder.…”

Section: Optimise the Processing Parametersmentioning

confidence: 99%

“…However, in most manufacturing situations it is desired to produce a fully dense part, as porosity can weaken the part and lead to early failure and reduced strength. Research has shown that there are two main forms of porosity in AM parts (Mertens et al, 2014) (Ng et al, 2009). For example, Mertens et al (2014) found two different forms of porosity in selective laser melted samples.…”

Section: Porosity In Ammentioning

confidence: 99%

“…The 'lack of melting' defects, also known as lack of fusion defects were attributed to insufficient melting of the newly deposited layer or insufficient remelting of the previous layer and can be noticed as lack of fusion between layers and around melt pools (Mertens et al, 2014). Entrapped gases porosity occurs due to entrapped gases in the solidified part (Ng et al, 2009). In general, the lack of fusion porosities are much larger than the entrapped gases porosity (Ng et al, 2009).…”

Section: Porosity In Ammentioning

confidence: 99%

“…In general, the lack of fusion porosities are much larger than the entrapped gases porosity (Ng et al, 2009). The occurrence of both of these types of porosity will depend on the chosen processing parameters and will depend on the thermal history of the part (Ng et al, 2009) .…”

Section: Porosity In Ammentioning

confidence: 99%

“…The amount of laser energy will also clearly affect the occurrence of lack of fusion defects as it determines the amount of heating (Ng et al, 2009). The laser energy can also determine the amount of entrapped gases as higher energy can increase turbulence in the melt pool and cause gases to be entrapped (Ng et al, 2009). The effect of processing parameters on the quality of AMED parts is discussed in detail in section 2.10.…”

Section: Porosity In Ammentioning

confidence: 99%

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Investigation into the effect of subsequent layer addition on the microstructure and properties of previous layers during direct laser deposition of 316L stainless steel

Robinson¹

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Additive manufacturing (AM) is a new and emerging technology in which further research is needed in order to make the most of its potential and unique benefits compared to conventional manufacturing. This current work helps to develop an understanding of AM processes by investigating the effect of subsequent layer addition on previous layers during direct laser deposition. As subsequent layers are added to a part, heat is transferred into previous layers, which may change the microstructure and properties of the pervious layers.There is no current research into the effect of these reheating cycles. In this work a new and innovative approach is used in which samples of different numbers of layers are produced and analysed, allowing the effect of reheating due to subsequent layer addition to be individually investigated. A LENS 450 system is used to produce samples of various numbers of layers (2 layer, 3 layer, 4 layer etc.) and the microstructure and hardness of the same layer in different samples is compared. Before the main research was performed the processing parameters were optimised for the LENS 450 system. It was determined that a powder feed rate of 5rpm, scanning speed of 18ipm and laser power of 300W produced the best component for this system, with a minimum amount of porosity. The optimum sample had only 0.34% porosity and a hardness of 203HV ± 23HV. The overall outcome of the work was that a generation of new knowledge about direct laser deposition processes was obtained, which will thus help in future development and control of AM processes. It was concluded that there was no significant change in properties with the subsequent layer addition due to the austenitic stainless steel exhibiting no phase changes on heating or cooling, which is a property unique to the austenitic stainless steels. END ii Acknowledgement

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Section: Optimise the Processing Parametersmentioning

confidence: 99%

Section: Porosity In Ammentioning

confidence: 99%

Section: Porosity In Ammentioning

confidence: 99%

Section: Porosity In Ammentioning

confidence: 99%

Section: Porosity In Ammentioning

confidence: 99%

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Investigation into the effect of subsequent layer addition on the microstructure and properties of previous layers during direct laser deposition of 316L stainless steel

Robinson¹

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Extreme‐Value Statistics Reveal Rare Failure‐Critical Defects in Additive Manufacturing

et al. 2017

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Additive manufacturing enables the rapid, cost effective production of customized structural components. To fully capitalize on the agility of additive manufacturing, it is necessary to develop complementary high-throughput materials evaluation techniques. In this study, over 1000 nominally identical tensile tests are used to explore the effect of process variability on the mechanical property distributions of a precipitation hardened stainless steel produced by a laser powder bed fusion process, also known as direct metal laser sintering or selective laser melting. With this large dataset, rare defects are revealed that affect only %2% of the population, stemming from a single build lot of material. The rare defects cause a substantial loss in ductility and are associated with an interconnected network of porosity. The adoption of streamlined test methods will be paramount to diagnosing and mitigating such dangerous anomalies in future structural components.

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Selective Laser Melting and Remelting of Pure Tungsten

et al. 2020

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The processing of pure tungsten encounters a substantial challenge due to its high melting point and intrinsic brittleness. Selective laser melting (SLM) technique is gaining popularity and offers an excellent processing approach for refractory metals. Herein, dense pure tungsten specimens are produced by optimizing SLM processing parameters. The mechanical property of the SLM‐produced tungsten with an ultimate compressive strength of about 1200 MPa, which is obviously superior to that reported in other literature, is achieved. The increased laser energy input is instrumental in raising density and surface roughness of tungsten specimens. Interestingly, additional remelting of processed layers during SLM improves the surface quality and the microstructure and achieves the highest relative density (98.4% ± 0.5%). After laser remelting, the surface roughness is reduced by 28% and a large number of fine grains are obtained. The flow of fluids caused by remelting plays a decisive role in the formation of fine grains and the defect level. Therefore, these findings offer a new insight into SLM of pure tungsten.

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Porosity formation and gas bubble retention in laser metal deposition

Cited by 172 publications

References 15 publications

Investigation into the effect of subsequent layer addition on the microstructure and properties of previous layers during direct laser deposition of 316L stainless steel

Investigation into the effect of subsequent layer addition on the microstructure and properties of previous layers during direct laser deposition of 316L stainless steel

Extreme‐Value Statistics Reveal Rare Failure‐Critical Defects in Additive Manufacturing

Selective Laser Melting and Remelting of Pure Tungsten

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