Fabrication of X-Graded H13 and Cu Powder Mix Using High Power Pulsed Nd:YAG Laser

The manufacturing of Functionally Graded Material (FGM) parts using Solid Free Form manufacturing technologies has been carried out since early 1980. At present, most of the powder manufacturing techniques are being focused on layering powder with different powder blend compositions with Z gradients (graded in direction of layer build). Although, there are a few researchers working on multi powder feeder and deposition system, the study of laser fusion of the deposited powder (by a powder deposition system) is minimum or not known to date. Consequently, the manufacturing of functionally graded structures is still geometry limited. This work was focused on the manufacturing of X-graded (graded along the powder bed plane) specimens with H13 tool steel and Cu mix. Five bimodal powder blends were used with a multi-container feed hopper to spread powder layers for the selective laser fusion of the powder. The powder was fused using a high power Nd:YAG pulsed laser using a specific scanning strategy to reduce porosity. Specimens were produced with graded Cu within the H13 matrix. The specimens were analysed for dimensional accuracy, microstructure, porosity, cracks and micro hardness of the FGM.Mechanical Engineerin

A Fluid-Dynamic Numerical Model for the Selective Laser Melting of High-Thickness Metallic Layers

Productivity in the Selective Laser Melting Process (SLM) is directly related with the thickness of the powder bed that is repeatedly applied, at every increment, in the growing of consolidated material in the additive manufacturing process. Although most of the relevant phenomena (limited diffusivity associated to particles contact, phase changes, gradients of surface tension associated with Marangoni convection, or even recoil pressure) are considered in the models with small bed thicknesses (roughly 20 µm ? 40 µm), in the case of larger thicknesses (between 100 µm and 200 µm) these factors strongly influence the size and shape of the fusion bath leading to a non trivial geometry of the final consolidated material. The present work proposes the use of the Arbitrary Lagrangean-Eulerian method (ALE method) to solve the thermal and Navier-Stokes equations in the frame of a free-moving discretization to predict simultaneously the space-time temperature evolution and the associated fusion bath dynamics. It allows for using a continuous domain to represent the powder bed, which, instead of a particle model approach, is advantageously compatible with realistic process parameters, where long paths are covered by the laser. The model was validated with experimental data using Inconel as working material, showing a good degree of agreement

Laser diode area melting for high speed additive manufacturing of metallic components

Additive manufacturing processes have been developed to a stage where they can now be routinely used to manufacture net-shape high-value components. Selective Laser Melting (SLM) comprises of either a single or multiple deflected high energy fibre laser source(s) to raster scan, melt and fuse layers of metallic powdered feedstock. However this deflected laser raster scanning methodology is high cost, energy inefficient and encounters significant limitations on output productivity due to the rate of feedstock melting. This work details the development of a new additive manufacturing process known as Diode Area Melting (DAM). This process utilises customised architectural arrays of low power laser diode emitters for high speed parallel processing of metallic feedstock. Individually addressable diode emitters are used to selectively melt feedstock from a pre-laid powder bed. The laser diodes operate at shorter laser wavelengths (808 nm) than conventional SLM fibre lasers (1064 nm) theoretically enabling more efficient energy absorption for specific materials. The melting capabilities of the DAM process were tested for low melting point eutectic BiZn2.7 elemental powders and higher temperature pre-alloyed 17-4 stainless steel powder. The process was shown to be capable of fabricating controllable geometric features with evidence of complete melting and fusion between multiple powder layers

High cycle fatigue and ratcheting interaction of laser powder bed fusion stainless steel 316L:Fracture behaviour and stress-based modelling

Variations in the physical and mechanical properties of parts made by laser power bed fusion (L-PBF) could be affected by the choice of processing or post-processing strategies. This work examined the influence of build orientation and post-processing treatments (annealing or hot isostatic pressing) on the fatigue and fracture behaviours of L-PBF stainless steel 316L in the high cycle fatigue region, i.e. 104 – 106 cycles. Experimental results show that both factors introduce significant changes in the plastic deformation properties, which affect fatigue strength via the mechanism of fatigue-ratcheting interaction. Cyclic plasticity is characterised by hardening, which promotes mean stress insensitivity and improved fatigue resistance. Fatigue activities, involving the initiation of crack at defects and microstructural heterogeneities, are of greater relevance to the longer life region where the global deformation mode is elastic. As the simultaneous actions of ratcheting and fatigue generate complex nonlinear interactions between the alternating stress amplitude and mean stress, the fatigue properties could not be effectively predicted using traditional stress-based models. A modification to the Goodman relation was proposed to account for the added effects of cyclic plasticity and was demonstrated to produce good agreement with experimental results for both cyclic hardening and softening materials.EDB (Economic Devt. Board, S’pore)Accepted versio

Solidification Morphology Analysis of SLM of Cu Powder

The solidification morphology analysis of fine Cu powder melted by a raster scanned energy beam from a focused Nd:YAG laser is presented here. The powder was processed inside of sealed chamber where it was subjected to a high vacuum cycle. The laser fusion process consisted raster scanning a narrow rectangular pattern with a high density of scanning lines, the chamber was purged with inert gas during the process. Up to a 3.3 mm/s laser travel speed and maximum laser power level of 240 W were used to melt a 2 mm thick bed of loose powder. The resulting solidified ingots were separated into categories based on their shape integrity. Metallographic analysis by means of optical microscopy and scanning electron microscopy was performed on the cross section and longitudinal section of the ingots with homogeneous surface and complete shape integrity. Characterization revealed an elongated columnar grain structure with a grain orientation along the direction of the laser travel direction, some degree of porosity was observed too in some of the specimens. It was observed that grains diameter ranged from 10 to 100 µm and contained a two phase eutectic microstructure of copper and it oxides. Oxygen content was accounted from a 5.5 up to 8.1 atomic percent, a small percentage of chlorine was present, too. A 2 to 8 percent variation in the Vickers microhardness values were found between the different specimens when measured along the longitudinal section. These HV values corresponded to approximate 20-25% cold rolled oxygen free copper (80-90 HV). The ingots thus produced suggest that a multilayer structure from Cu powder could be build by the SLM process having sufficiently adequate compositional, microstructure and mechanical properties for functional applications.Mechanical Engineerin

A scalable parallel finite element framework for growing geometries. Application to metal additive manufacturing

This work introduces an innovative parallel, fully-distributed finite element framework for growing geometries and its application to metal additive manufacturing. It is well-known that virtual part design and qualification in additive manufacturing requires highly-accurate multiscale and multiphysics analyses. Only high performance computing tools are able to handle such complexity in time frames compatible with time-to-market. However, efficiency, without loss of accuracy, has rarely held the centre stage in the numerical community. Here, in contrast, the framework is designed to adequately exploit the resources of high-end distributed-memory machines. It is grounded on three building blocks: (1) Hierarchical adaptive mesh refinement with octree-based meshes; (2) a parallel strategy to model the growth of the geometry; (3) state-of-the-art parallel iterative linear solvers. Computational experiments consider the heat transfer analysis at the part scale of the printing process by powder-bed technologies. After verification against a 3D benchmark, a strong-scaling analysis assesses performance and identifies major sources of parallel overhead. A third numerical example examines the efficiency and robustness of (2) in a curved 3D shape. Unprecedented parallelism and scalability were achieved in this work. Hence, this framework contributes to take on higher complexity and/or accuracy, not only of part-scale simulations of metal or polymer additive manufacturing, but also in welding, sedimentation, atherosclerosis, or any other physical problem where the physical domain of interest grows in time

Selective laser sintering of hydroxyapatite reinforced polyethylene composites for bioactive implants and tissue scaffold development

Selective laser sintering (SLS) has been investigated for the production of bioactive implants and tissue scaffolds using composites of high-density polyethylene (HDPE) reinforced with hydroxyapatite (HA) with the aim of achieving the rapid manufacturing of customized implants. Single-layer and multilayer block specimens made of HA-HDPE composites with 30 and 40 vol % HA were sintered successfully using a CO2 laser sintering system. Laser power and scanning speed had a significant effect on the sintering behaviour. The degree of particle fusion and porosity were influenced by the laser processing parameters, hence control can be attained by varying these parameters. Moreover, the SLS processing allowed exposure of HA particles on the surface of the composites and thereby should provide bioactive products. Pores existed in the SLS-fabricated composite parts and at certain processing parameters a significant fraction of the pores were within the optimal sizes for tissue regeneration. The results indicate that the SLS technique has the potential not only to fabricate HA-HDPE composite products but also to produce appropriate features for their application as bioactive implants and tissue scaffolds

Powder Bed Fusion Additive Manufacturing of JBK-75

JBK-75 is an iron-nickel derivative alloy of A-286 that has been of interest to NASAs propulsion community for use in fuel injectors and other components that are used in hot, corrosive environments. To enable the rapid production of these components in JBK-75, Marshall Space Flight Center has developed parameters for manufacturing fully dense JBK-75 components using powder bed fusion additive manufacturing (PBFAM). These parameters were developed in a two-step development. First, the depth of laser penetration in the powdered material was measured across a spectrum of laser powers to determine the optimal power necessary for generating the desired meltpool depth. The parameter sets vector-to-vector spacing was then then tailored to guarantee the full densification of the desired area. The results of this development was a readily implementable parameter that produced 99.6% dense material when using a 147W power running at 600mm/s with a 85m(32%) vector-to-vector spacing

Latest Developments in Industrial Hybrid Machine Tools that Combine Additive and Subtractive Operations

Hybrid machine tools combining additive and subtractive processes have arisen as a solution to increasing manufacture requirements, boosting the potentials of both technologies, while compensating and minimizing their limitations. Nevertheless, the idea of hybrid machines is relatively new and there is a notable lack of knowledge about the implications arisen from their in-practice use. Therefore, the main goal of the present paper is to fill the existing gap, giving an insight into the current advancements and pending tasks of hybrid machines both from an academic and industrial perspective. To that end, the technical-economical potentials and challenges emerging from their use are identified and critically discussed. In addition, the current situation and future perspectives of hybrid machines from the point of view of process planning, monitoring, and inspection are analyzed. On the one hand, it is found that hybrid machines enable a more efficient use of the resources available, as well as the production of previously unattainable complex parts. On the other hand, it is concluded that there are still some technological challenges derived from the interaction of additive and subtractive processes to be overcome (e.g., process planning, decision planning, use of cutting fluids, and need for a post-processing) before a full implantation of hybrid machines is fulfilledSpecial thanks are addressed to the Industry and Competitiveness Spanish Ministry for the support on the DPI2016-79889-R INTEGRADDI project and to the PARADDISE project H2020-IND-CE-2016-17/H2020-FOF-2016 of the European Union's Horizon 2020 research and innovation program