Multi material powder delivering systems for selective laser melting

Published ArticleSelective Laser Melting (SLM) is a powder bed fusion process which is an additive manufacturing (AM) process, whereby a laser beam selectively fuses regions of a powder bed to form complex objects. Growth in the SLM field has revealed the need for parts containing multiple materials for applications in the medical, tool making, aerospace and other hi-tech industries. By applying multiple materials, regions with different mechanical properties, thermal conductivity zones or corrosion-resistant coatings can be achieved in a single manufacturing cycle utilizing the SLM process. With the SLM process physical bonds can be formed between different materials by creating an interlocking interface due to the rapid solidification of the molten materials. With the current SLM equipment, multi material objects are possible but only with material differences between the layers. New approaches are needed to develop a method that allows multi material parts not only in the Z axis, but also allow material differences on a single layer (X-Y axis). Approaches such as powder feeding through a capillary tube, auger feed system, electrostatic charge or masks have all been proposed as solutions to multi material deposition. Multi material objects produced in a single cycle with complex geometry and prescribed properties has the opportunity of further growing the AM market

NON-DESTRUCTIVE TESTING OF THE PARTS MANUFACTURED BY DIRECT METAL LASER SINTERING

Published Conference ProceedingsInterest in Additive Manufacturing (AM) has grown considerably in the past decades. The industry has gained the great benefits from this type of technologies. The main advantages being geometrical freedom that allows designing parts with complex shape, which are difficult or impossible to produce by conventional technology, shortened design to product time, customization and possible use of several materials in one process. Direct Metal Laser Sintering (DMLS) is one of the most promising AM techniques that utilize metal materials. Due to the complex nature of the DMLS process, one of the drawbacks is the high residual stress in the manufactured parts. This can result to the formation of internal cracks and eventually to a substantial deterioration of the mechanical properties of the products and their application properties. For this reason it is very important to identify defective parts before enrolling into service. Non-destructive testing (NDT) is effective for detection of internal defects without causing damage. NDT also covers a wide group of methods of analysis used to evaluate the properties of a material. NDT techniques like ultrasonic inspection, acoustic emission, visual inspection, thermography, X-ray and 3D computed tomography (CT) inspection, etc. are now widely used for various industrial applications. For the detection of defects and to study the properties of the material each of these methods uses different physical principles that have their advantages and disadvantages. In this study some of the NDT techniques in terms of their applicability to the inspection of parts manufactured by DMLS technology are considered

IN-SITU ALLOYING PROCESS OF TI6AL4V-xCU STRUCTURES BY DIRECT METAL LASER SINTERING

Published Conference ProceedingsIn this paper the fabrication of in-situ Ti6Al4V-xCu alloy structures by DMLS are investigated. Ti6Al4V is a commonly used biomedical alloy because of it suitable mechanical and biocompatible properties. Copper is a proven anti-bacterial agent and in small amounts is not toxic to the human body. Ti6Al4V-xCu implants can be constructed to have a biocompatible structure with copper additions to reduce the risk of bacterial infection and implant failure. Infection at the bone–implant interface is the most probable reason for implant failure directly after implantation. Ti6Al4V powder was mixed with Cu powder to form a master alloy. Optimal process parameters need to be established for in-situ alloying of Ti6Al4V-xCu to form dense parts with suitable surface quality. The effect of laser scanning speeds and hatch distance on surface characteristics was investigated. The surface roughness, chemical composition and distribution of Cu near the surface and within the synthesized layer, as well as micro hardness were considered. A rescanning strategy was employed and showed improved alloy homogeneity and surface quality

METAL ADDITIVE MANUFACTURING OF BLENDED ELEMENTAL Ti-6Al-4V POWDERS

ArticleSouth Africa primarily produces titanium raw material as a TiO2 rich slag of which most is exported, without further value addition to the mineral. Therefore, powder development becomes a significant aspect of research with possibilities of growth within the titanium metal industry in South Africa. Commercially pure titanium has been successfully blended in conventional powder metallurgy processing, but the use of blended elemental powder to produce Ti-6Al-4V powder for metal additive manufacturing alloy parts has not been demonstrated yet. The objective of this study is to determine the feasibility of using blended elemental Ti-6Al-4V powder for use in a powder bed additive manufacturing (AM) system. In this paper a literature review and proposed methodology are presented and the expected outcomes are discussed

Qualification of Ti6Al4V ELI Alloy Produced by Laser Powder Bed Fusion for Biomedical Applications

Published ArticleTi6Al4V ELI samples were manufactured by Laser Powder Bed Fusion (LPBF) in vertical and horizontal directions and subjected to various heat treatments. Detailed analyses of porosity, microstructure, residual stress, tensile properties, fatigue and fractured surfaces were performed based on X-ray micro computed tomography, scanning electron microscopy and X-ray diffraction methods. Types of fractures and tensile fracture mechanisms in LPBF Ti6Al4V ELI alloy were studied. Detailed analysis of the microstructure and the corresponding mechanical properties were compared with standard specifications for conventional Ti6Al4V alloy (grade 5 and 23) for surgical implant applications. Conclusions regarding mechanical properties and heat treatment of LPBF Ti6Al4V ELI for biomedical applications were made

Manufacturing, microstructure and mechanical properties of selective laser melted Ti6Al4V-Cu

Conference ProceedingsTi6Al4V is a commonly used biomedical alloy because of its suitable mechanical and biocompatible properties. Infection at the bone–implant interface is the most probable reason for implant failure directly after implantation. Copper is a proven anti-bacterial agent and in small amounts is not toxic to the human body. Copper additions reduce the risk of bacterial infection and implant failure. Thus advanced implants can be constructed to have a biocompatibility and antibacterial properties. Optimal process parameters are needed to be established for in-situ alloying of Ti6Al4V-Cu to form dense parts with suitable mechanical properties. The effect of laser scanning speeds and hatch distance on morphology of single layers was investigated. The surface roughness, chemical composition and distribution of Cu near the surface and within the synthesized layer, as well as micro hardness were considered. An employed rescanning strategy showed improved alloy homogeneity and surface quality. On the base of these data 3D samples were produced. Microstructure and mechanical properties of as-built parts were analysed

Thermal stability of the cellular structure of an austenitic alloy after selective laser melting

Published ArticleThe thermal stability of the cellular structure of an austenitic Fe–17% Cr–12% Ni–2% Mo–1% Mn–0.7% Si–0.02% C alloy produced by selective laser melting in the temperature range 20–1200°C is investigated. Metallographic analysis, transmission electron microscopy, and scanning electron microscopy show that structural changes in the alloy begin at 600-700°C and are fully completed at ~1150°C. Differential scanning calorimetry of the alloy with a cellular structure reveals three exothermic processes occurring upon annealing within the temperature ranges 450–650, 800–1000, and 1050–1200°

Oxygen and nitrogen concentrations in the Ti-6Al-4V alloy manufactured by direct metal laser sintering (DMLS) process

Published ArticleTwo machines from two scientific centers (Russia and South Africa) were used for the manufacturing of the Ti6Al4V alloys by the direct metal laser sintering. The chemical composition of powders complies with the ASTM F-136 (grade 5), ASTM B348 (grade 23) standard for medical applications. Analysis of the oxygen and nitrogen contamination in DMLS alloys was done with Van de Graaff accelerator with two Mega Volts. It is found that structures of the samples manufactured with two different machines used the same regimes are close to each other. TEM studies found the metastable martensitic structure and silicon nitride Si3N4. It was found that the oxygen and nitrogen contents in both samples are within the normal range for medical grade titanium alloys

Influence Of Large Artificial Porosity On Bending Behaviour Of Ti6Al4V Eli Additively Manufactured Specimens Subjected To Typical Loads During Mastication

ArticleEffective quality control of implants made using additive manufacturing is an important task for suppliers to comply fully with existing regulations and certifications. To study the influence of porosity on the mechanical behaviour of mandibular implants produced by additive manufacturing, preliminary tests with longitudinal flat samples were performed with 3D point bending tests. Ti6Al4V Extra Low Interstitial (ELI) specimens with artificial porosity were designed and subjected to typical loads during mastication. In this work, a finite element simulation was constructed to investigate the bending behaviour of samples, which was consistent with the experimental results. The work shows that even large artificial cavities (designed up to 0.42 mm) do not significantly affect the strength of additively manufactured 2.5 mm-thick Ti6Al4V ELI specimens under typical static loads of mandibular implants, in the considered loading conditions, and for samples subjected to appropriate surface finishing and annealing heat treatment

Monitoring of Laser Powder Bed Fusion by Acoustic Emission: Investigation of Single Tracks and Layers

Quality concerns in laser powder bed fusion (L-PBF) include porosity, residual stresses and deformations during processing. Single tracks are the fundamental building blocks in L-PBF and their shape and geometry influence subsequent porosity in 3D L-PBF parts. The morphology of single tracks depends primarily on process parameters. The purpose of this paper is to demonstrate an approach to acoustic emission (AE) online monitoring of the L-PBF process for indirect defect analysis. This is demonstrated through the monitoring of single tracks without powder, with powder and in layers. Gas-borne AE signals in the frequency range of 2–20 kHz were sampled using a microphone placed inside the build chamber of a L-PBF machine. The single track geometry and shape at different powder thickness values and laser powers were studied together with the corresponding acoustic signals. Analysis of the acoustic signals allowed for the identification of characteristic amplitudes and frequencies, with promising results that support its use as a complementary method for in-situ monitoring and real-time defect detection in L-PBF. This work proves the capability to directly detect the balling effect that strongly affects the formation of porosity in L-PBF parts by AE monitoring