Influence of Small Particles Inclusion on Selective Laser Melting of Ti-6al-4v Powder

The particle size distribution and powder morphology of metallic powders have an important effect on powder bed fusion based additive manufacturing processes, such as selective laser melting (SLM). The process development and parameter optimization require a fundamental understanding of the influence of powder on SLM. This study introduces a pre-alloyed titanium alloy Ti-6Al-4V powder, which has a certain amount of small particles, for SLM. The influence of small particle inclusion is investigated through microscopy of surface topography, elemental and microstructural analysis, and mechanical testing, compared to the Ti-6Al-4V powder provided by SLM machine vendor. It is found that the small particles inclusion in Ti-6Al-4V powder has a noticeable effect on extra laser energy absorption, which may develop imperfections and deteriorate the SLM fatigue performance

Effects of Powder Variation on the Microstructure and Tensile Strength of Ti6Al4V Parts Fabricated by Selective Laser Melting

Metallic powders are used as raw materials in the Selective Laser Melting (SLM) process. These metal powders are typically available from more than one powder vendor. Even when powders have the same nominal chemical compositions, powders produced by different companies typically result in different powder particle size distributions and morphologies. These powder differences result in different powder bed thermophysical properties, which affect how the powder melts and solidifies. This paper studies the effect of powder variation on the microstructure and tensile strength of as-built SLM Ti6Al4V parts. Ti6Al4V powders from different vendors were used to fabricate parts via SLM. Powder characteristics, such as particle size distribution, morphology, and flowability, were obtained. Powder bed densities and thermal conductivities were measured and compared. The microstructures and tensile strengths were investigated by standard metallographic and tensile testing methods. Based on the experimental results, a correlation between the powder characteristics and part properties are discussed

Single Track of Selective Laser Melting Ti-6Al-4V Powder on Support Structure

Melt pool shows inconsistency due to the varied heat conditions in selective laser melting (SLM) process, even if identical process parameters are used. The characterization of the actual melt pool shape is highly desired in order to eventually control the quality and property of additive manufacturing products. It has been well understood that base plate provides high thermal conduction while powder bed is low thermal condition for fusion energy to be dissipated. Based on former study of melt pool characterization on a base plate, this study creates single tracks on the support structure, which is considered the similar heat condition of the Ti-6Al-4V powder bed. Various patterns of the support structure are fabricated for single track deposition, in order to investigate the effect of the support structure on melt pool consistency and continuity. Different laser melting parameters are used in the experiments to understand their effects on the melt pool morphology

Simulating Melt Pool Shape and Lack of Fusion Porosity for Selective Laser Melting of Cobalt Chromium Components

Cobalt chromium is widely used to make medical implants and wind turbine, engine and aircraft components because of its high wear and corrosion resistance. The ability to process geometrically complex components is an area of intense interest to enable shifting from traditional manufacturing techniques to additive manufacturing (AM). The major reason for using AM is to ease design modification and optimization since AM machines can directly apply the changes from an updated STL file to print a geometrically complex object. Quality assurance for AM fabricated parts is recognized as a critical limitation of AM processes. In selective laser melting (SLM), layer by layer melting and remelting can lead to porosity defects caused by lack of fusion, balling, and keyhole collapse. Machine process parameter optimization becomes a very important task and is usually accomplished by producing a large amount of experimental coupons with different combinations of process parameters such as laser power, speed, hatch spacing, and powder layer thickness. In order to save the cost and time of these experimental trial and error methods, many researchers have attempted to simulate defect formation in SLM. Many physics-based assumptions must be made to model these processes, and thus, all the models are limited in some aspects. In the present work, we investigated single bead melt pool shapes for SLM of CoCr to tune the physics assumptions and then, applied to the model to predict bulk lack of fusion porosity within the finished parts. The simulation results were compared and validated against experimental results and show a high degree of correlation