RESIDUAL STRESS IN TI6AL4V OBJECTS PRODUCED BY DIRECT METAL LASER SINTERING

Published ArticleDirect Metal Laser Sintering produces 3D objects using a layer-by-layer method in which powder is deposited in thin layers. Laser beam scans over the powder fusing powder particles as well as the previous layer. High-concentration of laser energy input leads to high thermal gradients which induce residual stress within the as-built parts. Ti6Al4V (ELI) samples have been manufactured by EOSINT M280 system at prescribed by EOS process-parameters. Residual stresses were measured by XRD method. Microstructure, values and directions of principal stresses inTi6Al4V DMLS samples were analysed

ON THE IMPACT OF DIFFERENT SYSTEM STRATEGIES ON THE MATERIAL PERFORMANCE OF SELECTIVE LASER MELTING- MANUFACTURED TI6AL4V COMPONENTS

Selective Laser Melting (SLM) is a powder-based additive manufacturing process that has gained substantial interest in recent years due to its feasibility of producing geometrically- complex metallic components for end-use in various industries, with or without post-treatment procedures. This paper presents recent research undertaken on different scanning strategies and process parameters with the purpose of providing an overview of the achievable material performance of Ti6Al4V components, and comparing its properties with the conventionally-produced parts. In order to understand their output, differences in the building strategies of the systems studied are analysed, and their influence on the resulting mechanical and metallurgical properties is highlighted

Effect of Process Parameters on Residual Stresses, Distortions, and Porosity in Selective Laser Melting of Maraging Steel 300

Published ArticleSelective laser melting (SLM) is one of the most well-known additive manufacturing methods available for the fabrication of functional parts from metal powders. Although SLM is now an established metal additive manufacturing technique, its widespread application in industry is still hindered by inherent phenomena, one of which is high residual stresses. Some of the e ects of residual stresses–such as warping and thermal stress-related cracking–cannot be corrected by post processing. Therefore, establishing input process parameter combinations that result in the least residual stress magnitudes and related distortions and/or cracking is critical. This paper presents the influence of laser power, scanning speed, and layer thickness on residual stresses, distortions and achievable density for maraging steel 300 steel parts in order to establish the most optimum input parameter combinations. An analysis of the interdependence between process outcomes shows that high residual stress magnitudes lead to high dimensional distortions in the finished parts, whilst porous parts su er relatively lower residual stresses and associated distortions

RESIDUAL STRESS IN TI6AL4V OBJECTS PRODUCED BY DIRECT METAL LASER SINTERING

Direct Metal Laser Sintering produces 3D objects using a layer-by- layer method in which powder is deposited in thin layers. Laser beam scans over the powder fusing powder particles as well as the previous layer. High-concentration of laser energy input leads to high thermal gradients which induce residual stress within the as- built parts. Ti6Al4V (ELI) samples have been manufactured by EOSINT M280 system at prescribed by EOS process-parameters. Residual stresses were measured by XRD method. Microstructure, values and directions of principal stresses inTi6Al4V DMLS samples were analysed

Characterization of 17-4ph single tracks produced at different parametric conditions towards increased productivity of lpbf systems—the effect of laser power and spot size upscaling

Global industrial adoption of laser-based powder bed fusion (LPBF) technology is still limited by the production speed, the size of the build envelope, and therefore the maximum part size that can be produced. The cost of LPBF can be driven down further by improving the build rates without compromising structural integrity. A common approach is that the build rate can be improved by increasing the laser power and beam diameter to instantly melt a large area of powder, thus reducing the scanning time for each layer. The aim of this study was to investigate the aspects of upscaling LPBF processing parameters on the characteristic formation of stable single tracks, which are the primary building blocks for this technology. Two LPBF systems operating independently, using different parameter regimes, were used to produce the single tracks on a solid substrate deposited with a thin powder layer. The results obtained indicate that higher laser power and spot size can be used to produce stable tracks while the linear energy input is increased. It was also shown statistically that the geometrical characteristics of single tracks are mainly affected by the laser power and scanning speed during the scanning of a thin powder layer.The Department of Science and Technology and National Research Foundation of South Africa (Grant number 97994).http://www.mdpi.com/journal/metalsam2018Materials Science and Metallurgical Engineerin

On the impact of different system strategies on the material performance of selective laser melting- manufactured TI6AL4V components

CITATION: Dimitrov, D., et al. 2016. On the impact of different system strategies on the material performance of selective laser melting- manufactured TI6AL4V components. South African Journal of Industrial Engineering, 27(3):84-191, doi:10.7166/27-3-1664.The original publication is available at http://sajie.journals.ac.za/pubENGLISH ABSTRACT: Selective Laser Melting (SLM) is a powder-based additive manufacturing process that has gained substantial interest in recent years due to its feasibility of producing geometrically- complex metallic components for end-use in various industries, with or without post-treatment procedures. This paper presents recent research undertaken on different scanning strategies and process parameters with the purpose of providing an overview of the achievable material performance of Ti6Al4V components, and comparing its properties with the conventionally-produced parts. In order to understand their output, differences in the building strategies of the systems studied are analysed, and their influence on the resulting mechanical and metallurgical properties is highlighted.AFRIKAANSE OPSOMMING: Selektiewe lasersmelting is ʼn poeiergebaseerde toevoegingsver-vaardigingsproses wat onlangs wesenlike belangstelling gewek het as gevolg van die vermoë om geometries ingewikkelde metaal komponente te produseer sonder dat daar agteraf verdere behan-delinge toegepas moet word. Navorsing oor verskillende skandeerstrategieë en proses parameters en hul invloed op die bereikbare materiaaleienskappe van Ti6Al4V komponente word voorgehou. Die materiaaleienskappe word vergelyk met dié van komponente wat met konvensionele tegnieke vervaardig is. Om die uitset beter te verstaan, word verskille in die bou-strategieë van die stelsels bestudeer en analiseer, om sodoende hul invloed op die gevolglike meganiese- en metallurgiese eienskappe te bepaal.http://sajie.journals.ac.za/pub/article/view/1664Publisher's versio

Prediction of mechanical performance of Ti6Al4V cast alloy based on microCT-based load simulation

Published ArticleThe effect of porosity on the mechanical properties of cast titanium alloy was investigated in this work, specifically for investment-cast Ti6Al4V. X-ray micro computed tomography (microCT) was used to nondestructively analyse pores in 10 samples prior to mechanical testing. A finite element analysis was done on the microCT data providing a 3D view and quantitative values for maximum stress areas. All 10 samples were again analysed by X-ray microCT after physical testing. This allowed the location of failure to be correlated to pores and regions of high stress from the calculations. All samples showed high tensile strength with little effect of the pore size or simulated stress, most likely due to the simplified casting geometry. Irrespective of the microstructure, it was found that an increasing pore size results in increasing simulated stresses around the pores, which correlate strongly with a decrease in the measured ductility of the samples. This result indicates that induced stresses when a sample is put under load affects the ductility, since ductility depends on stress state of the material. Moderate correlation of the simulated stresses with ultimate tensile strength was found for samples with homogeneous microstructure

Effect of Heat Treatment on Osteoblast Performance and Bactericidal Behavior of Ti6Al4V(ELI)-3at.%Cu Fabricated by Laser Powder Bed Fusion

Cu addition to alloys for biomedical applications has been of great interest to reduce bac-terial growth. In situ-alloyed Ti6Al4V(ELI)-3at.%Cu was successfully manufactured by laser pow-der bed fusion (L-PBF). Even so, post-heat treatments are required to avoid distortions and/or achieve required/desired mechanical and fatigue properties. The present study is focused on the investigation of microstructural changes in L-PBF Ti6Al4V(ELI)-3at.%Cu after stress relieving and annealing treatments, as well as their influence on osteoblast and bactericidal behavior. After the stress relieving treatment, a homogenously distributed β phase and CuTi2 intermetallic precipitates were observed over the αʹ matrix. The annealing treatment led to the increase in amount and size of both types of precipitates, but also to phase redistribution along α lamellas. Although microstruc-tural changes were not statistically significant, such increase in β and CuTi2 content resulted in an increase in osteoblast proliferation after 14 days of cell culture. A significant bactericidal behavior of L-PBF Ti6Al4V(ELI)-3at.%Cu by means of ion release was found after the annealing treatment, provably due to the easier release of Cu ions from β phase. Biofilm formation was inhibited in all on Cu-alloyed specimens with stress relieving but also annealing treatment

Investigation of the effect of scan vector length on residual stresses in selective laser melting of maraging steel 300

CITATION: Mugwagwa, L., et al. 2019. Investigation of the effect of scan vector length on residual stresses in selective laser melting of maraging steel 300. South African Journal of Industrial Engineering, 30(4):60-70, doi:10.7166/30-4-2096.The original publication is available at http://sajie.journals.ac.zaENGLISH ABSTRACT: Selective laser melting scanning strategies influence the quality characteristics of parts, such as form accuracy and residual stresses. Previous research on the effect of laser scanning strategy parameters (such as scan vector length) demonstrates that residual stresses decrease with scan vector length reduction. However, most of these studies overlook the associated porosity and how this can contribute to stress relief. In this work, three scan vector lengths were compared to evaluate their impact on residual stresses, achievable part density, and scanning time. Reducing the scan vector length generally lowers residual stresses magnitudes, but introduces porosity as a result of localised overheating.AFRIKAANSE OPSOMMING: Selektiewe lasersmelt skanderingstrategieë beïnvloed die gehalte eienskappe van onderdele, soos vorm akkuraatheid en res-spannings. Vorige navorsing oor die invloed van laserskandeerstrategie parameters (soos vektorlengte) demonstreer dat res-spannings verminder met ʼn toename in skandeervektor lengte. Die meeste van hierdie studies neem egter nie die gepaardgaande poreusheid (en hoe dit kan bydra tot spanningverligting) in ag nie. In hierdie studie word drie skandeervektor lengtes vergelyk om die invloed daarvan op resspannings, bereikbare onderdeeldigtheid en skandeertyd te evalueer. Deur die skandeervektor lengte te verkort het oor die algemeen gelei tot verlaagde res-spannings, maar veroorsaak poreusheid as gevolg van lokale oorverhitting.http://sajie.journals.ac.za/pub/article/view/2096Publisher's versio

Evaluation of Residual Stress in Selective Laser Melting of 316L Steel

Selective Laser Melting (SLM) has great potential in additive manufacturing methods because it allows producing full density complex parts with desired inner structure and surface morphology. Mechanical properties of SLM objects depend strongly on the material properties as well as strength of the connections between tracks and layers since all objects made by SLM are superposition of the single tracks and single layers. High temperature gradient as a result of the locally concentrated energy input can lead to residual stresses, crack formation and part deformations both during laser processing and after cutting objects from the substrate. X-ray diffraction method was used for investigation of residual stress in SLM samples from 316L steel fabricated by one-zone strategy with 50% overlap of the tracks. Samples had rectangular shape and different thickness: 50 µm (one layer), 0.2 mm (5 layers) and 1 mm (25 layers). All as-made samples attached to the substrate had the tensile stress. Normal residual stress along the scan direction was 1.2-1.7 times higher than perpendicular direction. In some areas residual stress was about and exceeded the yield strength of 316L wrought material.Published versio