Search results

1 – 10 of 874
To view the access options for this content please click here
Article

Haihua Wu, Junfeng Li, Zhengying Wei and Pei Wei

To fabricate a selective laser melting (SLM)-processed AlSi10Mg part with almost full density and free of any apparent pores, this study aims to investigate the effect of…

Abstract

Purpose

To fabricate a selective laser melting (SLM)-processed AlSi10Mg part with almost full density and free of any apparent pores, this study aims to investigate the effect of ambient argon pressure and laser scanning speed on the particles splash during the AlSi10Mg powder bed laser melting.

Design/methodology/approach

Based on the discrete element method (DEM), a 3D model of random distribution of powder particles was established, and the 3D free surface of SLM forming process was dynamically tracked by the volume of fluid, where a Gaussian laser beam acts as the energy source melting the powder bed. Through the numerical simulation and process experimental research, the effect of the applied laser power and scanning speed on the operating laser melting temperature was studied.

Findings

The process stability has a fundamental role in the porosity formation, which is process-dependent. The effect of the processing conditions on the process stability and the resultant forming defects were clarified.

Research limitations/implications

The results shows that the pores were the main defects present in the SLM-processed AlSi10Mg sample, which decreases the densification level of the sample.

Practical implications

The optimal processing parameters (argon pressure of 1,000 Pa, laser power of 180 W, scan speed of 1,000 mm/s, powder layer thickness of 35 µm and hatch spacing of 50 µm ) applied during laser melting can improve the quality of selective laser melting of AlSi10Mg,

Social implications

It can provide a technological support for 3D printing.

Originality/value

Based on the analysis of the pore and balling formation mechanisms, the optimal processing parameters have been obtained, which were argon pressure of 1,000 Pa, laser power of 180 W, scan speed of 1,000 mm/s, powder layer thickness of 35 µm and hatch spacing of 50 µm. Then, a near-fully dense sample free of any apparent pores on the cross-sectional microstructure was produced by SLM, wherein the relative density of the as-built samples is larger than 97.5%.

Details

Rapid Prototyping Journal, vol. 26 no. 5
Type: Research Article
ISSN: 1355-2546

Keywords

To view the access options for this content please click here
Article

Di Wang, Yang Liu, Yongqiang Yang and Dongming Xiao

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…

Abstract

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.

Details

Rapid Prototyping Journal, vol. 22 no. 4
Type: Research Article
ISSN: 1355-2546

Keywords

To view the access options for this content please click here
Article

Swee Leong Sing, Wai Yee Yeong, Florencia Edith Wiria, Bee Yen Tay, Ziqiang Zhao, Lin Zhao, Zhiling Tian and Shoufeng Yang

This paper aims to provide a review on the process of additive manufacturing of ceramic materials, focusing on partial and full melting of ceramic powder by a high-energy…

Abstract

Purpose

This paper aims to provide a review on the process of additive manufacturing of ceramic materials, focusing on partial and full melting of ceramic powder by a high-energy laser beam without the use of binders.

Design/methodology/approach

Selective laser sintering or melting (SLS/SLM) techniques are first introduced, followed by analysis of results from silica (SiO2), zirconia (ZrO2) and ceramic-reinforced metal matrix composites processed by direct laser sintering and melting.

Findings

At the current state of technology, it is still a challenge to fabricate dense ceramic components directly using SLS/SLM. Critical challenges encountered during direct laser melting of ceramic will be discussed, including deposition of ceramic powder layer, interaction between laser and powder particles, dynamic melting and consolidation mechanism of the process and the presence of residual stresses in ceramics processed via SLS/SLM.

Originality/value

Despite the challenges, SLS/SLM still has the potential in fabrication of ceramics. Additional research is needed to understand and establish the optimal interaction between the laser beam and ceramic powder bed for full density part fabrication. Looking into the future, other melting-based techniques for ceramic and composites are presented, along with their potential applications.

Details

Rapid Prototyping Journal, vol. 23 no. 3
Type: Research Article
ISSN: 1355-2546

Keywords

To view the access options for this content please click here
Article

Abid Ullah, HengAn Wu, Asif Ur Rehman, YinBo Zhu, Tingting Liu and Kai Zhang

The purpose of this paper is to eliminate Part defects and enrich additive manufacturing of ceramics. Laser powder bed fusion (L-PBF) experiments were carried to…

Abstract

Purpose

The purpose of this paper is to eliminate Part defects and enrich additive manufacturing of ceramics. Laser powder bed fusion (L-PBF) experiments were carried to investigate the effects of laser parameters and selective oxidation of Titanium (mixed with TiO2) on the microstructure, surface quality and melting state of Titania. The causes of several L-PBF parts defects were thoroughly analyzed.

Design/methodology/approach

Laser power and scanning speed were varied within a specific range (50–125 W and 170–200 mm/s, respectively). Furthermore, varying loads of Ti (1%, 3%, 5% and 15%) were mixed with TiO2, which was selectively oxidized with laser beam in the presence of oxygen environment.

Findings

Part defects such as cracks, pores and uneven grains growth were widely reduced in TiO2 L-PBF specimens. Increasing the laser power and decreasing the scanning speed shown significant improvements in the surface morphology of TiO2 ceramics. The amount of Ti material was fully melted and simultaneously changed into TiO2 by the application of the laser beam. The selective oxidation of Ti material also improved the melting condition, microstructure and surface quality of the specimens.

Originality/value

TiO2 ceramic specimens were produced through L-PBF process. Increasing the laser power and decreasing the scanning speed is an effective way to sufficiently melt the powders and reduce parts defects. Selective oxidation of Ti by a high power laser beam approach was used to improve the manufacturability of TiO2 specimens.

To view the access options for this content please click here
Article

Chi Chung Ng, Monica Savalani and Hau Chung Man

Magnesium has been considered as a new generation of bioactive and biodegradable implant for orthopaedic applications because of its prominent properties including…

Abstract

Purpose

Magnesium has been considered as a new generation of bioactive and biodegradable implant for orthopaedic applications because of its prominent properties including superior biocompatibility, biodegradability and proper mechanical stiffness. For the direct production of custom biomedical implants, selective laser melting (SLM) has been investigated to fabricate pure magnesium and its resultant properties. The primary objective of this paper is to identify the most appropriate mode of irradiation for the melting of pure magnesium powders due to its reactive properties. This study focuses on investigating the interaction between the laser source and the magnesium powders by varying the SLM parameters of the laser power and scan speed under continuous or pulse mode conditions.

Design/methodology/approach

Single magnesium tracks were fabricated under different processing conditions using SLM, in order to evaluate the effects of processing parameters on the dimension and surface morphology of the achieved parts. The digital images of the tracks were used to analyze the geometrical features in terms of melting width and depth. In addition, scanning electron images were also studied to understanding the selective melting mechanism.

Findings

Magnesium tracks were successfully fabricated using SLM. Results showed that the dimension, surface morphology and the oxygen pick‐up of the lasermelted tracks are strongly dependent on the mode of irradiation and processing parameters.

Originality/value

This work is a first step towards magnesium fabrication using SLM technique. The experimental results represent an important step in understanding the magnesium under an Nd:YAG laser irradiation, which provides the basis of behavior for follow‐on research and experiments.

Details

Rapid Prototyping Journal, vol. 17 no. 6
Type: Research Article
ISSN: 1355-2546

Keywords

To view the access options for this content please click here
Article

Evren Yasa, Jan Deckers and Jean‐Pierre Kruth

Selective laser melting (SLM) is a powder metallurgical (PM) additive manufacturing process whereby a three‐dimensional part is built in a layer‐wise manner. During the…

Abstract

Purpose

Selective laser melting (SLM) is a powder metallurgical (PM) additive manufacturing process whereby a three‐dimensional part is built in a layer‐wise manner. During the process, a high intensity laser beam selectively scans a powder bed according to the computer‐aided design data of the part to be produced and the powder metal particles are completely molten. The process is capable of producing near full density (∼98‐99 per cent relative density) and functional metallic parts with a high geometrical freedom. However, insufficient surface quality of produced parts is one of the important limitations of the process. The purpose of this study is to apply laser re‐melting using a continuous wave laser during SLM production of 316L stainless steel and Ti6Al4V parts to overcome this limitation.

Design/methodology/approach

After each layer is fully molten, the same slice data are used to re‐expose the layer for laser re‐melting. In this manner, laser re‐melting does not only improve the surface quality on the top surfaces, but also has the potential to change the microstructure and to improve the obtained density. The influence of laser re‐melting on the surface quality, density and microstructure is studied varying the operating parameters for re‐melting such as scan speed, laser power and scan spacing.

Findings

It is concluded that laser re‐melting is a promising method to enhance the density and surface quality of SLM parts at a cost of longer production times. Laser re‐melting improves the density to almost 100 per cent whereas 90 per cent enhancement is achieved in the surface quality of SLM parts after laser re‐melting. The microhardness is improved in the laser re‐molten zone if sufficiently high‐energy densities are provided, probably due to a fine‐cell size encountered in the microstructure.

Originality/value

There has been extensive research in the field of laser surface modification techniques, e.g. laser polishing, laser hardening and laser surface melting, applied to bulk materials produced by conventional manufacturing processes. However, those studies only relate to laser enhancement of surface or sub‐surface properties of parts produced using bulk material. They do not aim at enhancement of core material properties, nor surface enhancement of (rough) surfaces produced in a PM way by SLM. This study is carried out to cover the gap and analyze the advantages of laser re‐melting in the field of additive manufacturing.

Details

Rapid Prototyping Journal, vol. 17 no. 5
Type: Research Article
ISSN: 1355-2546

Keywords

To view the access options for this content please click here
Article

Barry Haworth, John R. Tyrer and Zhou Zhou

There is a requirement to match selective laser melting (SLM) technologies to a wider range of polymeric materials, as the existing market for SLM powders is dominated by…

Abstract

Purpose

There is a requirement to match selective laser melting (SLM) technologies to a wider range of polymeric materials, as the existing market for SLM powders is dominated by polyamide PA12. Drivers include the tailoring of physical properties to individual applications or cost reduction. Polypropylene (PP) currently has limited use in SLM; so, this paper aims to explore the potential use of PP materials of varying molecular weight (Mw).

Design/methodology/approach

PP polymers of differing Mw were characterised using a range of analytical techniques, including differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), rotational rheometry and real-time hot-stage (optical) microscopy.

Findings

The techniques are sufficiently sensitive to distinguish Mw effects, notably in terms of material viscosity. The stable sintering region for SLM has been defined clearly. Some success was achieved in melting parts using all grades of PP, including higher Mw grades, which potentially offer improved mechanical performance.

Research limitations/implications

The range of techniques (DSC, oxidative induction time and TGA) form an effective analytical package with which to consider new polymeric materials for SLM.

Practical implications

High-Mw PP polymers, in tape or powder form, have potential use in SLM processes, providing scope to enhance part properties in future.

Originality/value

This is believed to be the first in-depth study noting the influence of PP Mw on important physical performance in a proprietary SLM process, using holographic beam manipulation.

Details

Rapid Prototyping Journal, vol. 24 no. 1
Type: Research Article
ISSN: 1355-2546

Keywords

To view the access options for this content please click here
Article

Mushtaq Khan and Phill Dickens

Different metals have been processed using laser‐based solid freeform fabrication (SFF) processes but very little work has been published on the selective laser melting

Abstract

Purpose

Different metals have been processed using laser‐based solid freeform fabrication (SFF) processes but very little work has been published on the selective laser melting (SLM) of gold (Au). The purpose of this paper is to check the properties of gold powder and identify suitable processing parameters for SLM of 24 carat gold powder.

Design/methodology/approach

A full factorial approach was used to vary the processing parameters and identify suitable processing region for gold powder. The effects of laser processing parameters on the internal porosity of the multi‐layer parts were examined.

Findings

The gold powder was found to be cohesive in nature with apparent and tap densities of 9.3 and 10.36 g/cm3, respectively. The reflectance of gold powder was found to be 85 per cent in the infrared range. A very narrow good melting region was identified for gold powder. The balling phenomenon was observed at both low and high scan speeds. The size of droplets in the balling region tended to increase with increasing laser power and decreasing scan speeds. The porosity in gold multi‐layer parts was found to be the minimum for a laser power of 50 W and scan speed of 65 mm/s where most of the porosity was found to be inter‐layer porosity.

Originality/value

This research is the first of its kind directly processing 24 carat gold using SLM, identifying the suitable processing parameters and its effect on the internal porosity and structure of multi‐layer parts.

Details

Rapid Prototyping Journal, vol. 18 no. 1
Type: Research Article
ISSN: 1355-2546

Keywords

To view the access options for this content please click here
Article

Pei Wei, Zhengying Wei, Zhne Chen, Jun Du, Yuyang He and Junfeng Li

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…

Abstract

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.

Details

Rapid Prototyping Journal, vol. 25 no. 9
Type: Research Article
ISSN: 1355-2546

Keywords

To view the access options for this content please click here
Article

J‐P. Kruth, P. Mercelis, J. Van Vaerenbergh, L. Froyen and M. Rombouts

This paper provides an overview of the different binding mechanisms in selective laser sintering (SLS) and selective laser melting (SLM), thus improving the understanding…

Abstract

Purpose

This paper provides an overview of the different binding mechanisms in selective laser sintering (SLS) and selective laser melting (SLM), thus improving the understanding of these processes.

Design/methodology/approach

A classification of SLS/SLM processes was developed, based on the binding mechanism occurring in the process, in contrast with traditional classifications based on the processed material or the application. A broad range of commercial and experimental SLS/SLM processes – found from recent articles as well as from own experiments – was used to explain the different binding mechanism categories.

Findings

SLS/SLM processes can be classified into four main binding mechanism categories, namely “solid state sintering”, “chemically induced binding”, “liquid phase sintering – partial melting” and “full melting”. Most commercial processes can be classified into the latter two categories, which are therefore subdivided. The binding mechanism largely influences the process speed and the resulting part properties.

Research limitations/implications

The classification presented is not claimed to be definitive. Moreover some SLM/SLM processes could be classified into more than one category, based on personal interpretation.

Originality/value

This paper can be a useful aid in understanding existing SLS/SLM processes. It can also serve as an aid in developing new SLS/SLM processes.

Details

Rapid Prototyping Journal, vol. 11 no. 1
Type: Research Article
ISSN: 1355-2546

Keywords

1 – 10 of 874