Rapid Steel Tooling Via Solid Freeform Fabrication

With increasing part complexity and requirements for long production runs, tooling has become an expensive process that requires long lead times to manufacture. This lengthens the amount oftime from "art to part". Rapid tooling via stereolithography (SLA), filled epoxies, etc. have been stopgap measures to produce limited prototyping runs from (10 to 500 parts). This gives poor dimensional analysis and does not allow for limited production runs of 1000+ parts. The method ofproducing prototype tooling with a powdered metal process has been developed that produces tooling with a hardness greater than 35 HRC and total shrinkage less than 0.5%. This tooling process manufactures production ready tooling that will perform extended cycle runs (100,000+). Manufacturing ofthis tooling takes 1 to 2 weeks and will compare favorably with production grade steel tooling. Originals drawn in 3D CAD can be used to prototype the master that will allow for the production ofthe rapid metal tool set. process starts with a rapid prototyped model made by whatever process is desired or a machined master. For this paper a Sander's Model Maker II® rapid prototyping machine was used to fabricate the model. After the model ofthe tool set is made, a silicone rubber negative is cast around that model. After the silicone rubber model is made, a heated slurry ofmetal powders and polymers is poured into the mold to create the green tool set. The tool set is left to cool, and then removed from the silicone rubber mold. The tool set is then debound and sintered to produce a final tool set with properties approaching hardened tool steel.Mechanical Engineerin

Effects of Hot Isostatic Pressing on the Properties of Laser-Powder Bed Fusion Fabricated Water Atomized 25Cr7Ni Stainless Steel

25Cr7Ni stainless steel (super duplex stainless steels) exhibits a duplex microstructure of ferrite and austenite, resulting in an excellent combination of high strength and corrosion resistance. However, Laser-Powder Bed Fusion fabrication of a water-atomized 25Cr7Ni stainless steel of novel chemical composition resulted in a purely ferritic microstructure and over 5% porosity. The current study investigated the effects of two hot isostatic pressing parameters on the physical, mechanical, and corrosion properties as well as microstructures of water-atomized 25Cr7Ni stainless steel of novel composition fabricated by L-PBF for the first time in the literature. The corrosion behaviour was studied using linear sweep voltammetry in a 3.5% NaCl solution. The Hot Isostatic Pressing-treated sample achieved over 98% densification with a corresponding reduction in porosity to less than 0.1% and about 3 similar to 4% in annihilation of dislocation density. A duplex microstructure of ferrite 60% and austenite 40%was observed in the X-Ray Diffraction and etched metallography of the HIP-treated samples from a purely ferritic microstructure prior to the HIP treatment. With the evolution of austenite phase, the HIP-treated samples recorded a decrease in Ultimate Tensile Strength, yield strength, and hardness in comparison with as-printed samples. The variation in the morphology of the evolved austenite grains in the HIP-treated samples was observed to have a significant effect on the elongation. With a reduction in porosity and the evolution of the austenite phase, the HIP-treated samples showed a higher corrosion resistance in comparison with the as-printed samples

Powder Injection Molding of Ceria-Stabilized, Zirconia-Toughened Mullite Parts for UAV Engine Components

Powder injection molding (PIM) of ceria-stabilized, zirconia-toughened mullite composites were investigated in the present article with the goal of obtaining performance enhancement in complex geometries for energy and transportation applications. A powder-polymer mixture (feedstock) was developed and characterized to determine its suitability for fabricating complex components using the PIM process. Test specimens were injection molded and subsequently debound and sintered. The sintered properties indicated suitable properties for engine component applications used in unmanned aerial vehicles (UAVs). The measured feedstock properties were used in computer simulations to assess the mold-filling behavior for a miniature turbine stator. The results from the measurements of rheological and thermal properties of the feedstock combined with the sintered properties of the ceria-stabilized, zirconia-toughened mullite strongly indicate the potential for enhancing the performance of complex geometries used in demanding operating conditions in UAV engines

Effects of atomizing media and post processing on mechanical properties of 17-4 PH stainless steel manufactured via selective laser melting

Water-atomized and gas-atomized 17-4 PH stainless steel powder were used as feedstock in selective laser melting process. Gas atomized powder revealed single martensitic phase after printing and heat treatment independent of energy density. As-printed water atomized powder contained dual martensitic and austenitic phase regardless of energy density. The H900 heat treatment cycle was not effective in enhancing mechanical properties of the water-atomized powder after laser melting. However, after solutionizing at 1315 degrees C and aging at 482 degrees C fully martensitic structure was observed with hardness (40.2 HRC), yield strength (1000 MPa) and ultimate tensile strength (1261 MPa) comparable to those of gas atomized (42.7 HRC, 1254 MPa and 1300 MPa) and wrought alloy (39 HRC, 1170 MPa and 1310 MPa), respectively. Improved mechanical properties in water-atomized powder was found to be related to presence of finer martensite and higher volume fraction of fine Cu-enriched precipitates. Our results imply that water-atomized powder is a promising cheaper feedstock alternative to gas-atomized powder

The Effects of Nanoparticle Addition on Binder Removal from Injection Molded Aluminum Nitride

The effects of nanoparticle addition on the multi-step debinding of injection molded aluminum nitride (AlN) samples were studied. Experiments varying the solvent debinding conditions (time, temperature and aspect ratio) were performed on monomodal, microscale (μ) and bimodal, micro-nanoscale (μ-n) AlN samples. Variations in the solvent debinding kinetics as a result of the reduced particle size and increased powder content were examined. The bimodal μ-n AlN samples showed a slower solvent extraction of binder components compared to monomodal μ-AlN samples. The activation energy for solvent extraction estimated from diffusion coefficients (Arrhenius equation) was in close agreement with the value estimated by the master debinding curve (MDC) method. An activation value around 50 kJ/mole was estimated by both the methods for μ and μ-n AlN samples. The thermal debinding behavior of dewaxed samples was also studied and the trends correlated with the solvent debinding behavior.Keywords: Master debinding curves, Diffusion coefficients, Solvent debinding, Bimodal, Activation energy, Monomoda

Composites Part B: Engineering

Coronary artery disease (CAD) is the narrowing or blockage of the coronary arteries, usually caused by atherosclerosis. An interventional procedure using stents is a promising approach for treating CAD because stents can effectively open narrowed coronary arteries to improve blood flow to the heart. However, stents often suffer from catastrophic failures, such as fractures and migration of ligaments, resulting in fatal clinical events. In this work, we report a new type of tubular lattice metamaterial with enhanced mechanical resilience under radial compression, which can be used as an alternative for the current stent design. We begin by comparing the radial mechanical performance of the proposed auxetic tubular lattice (ATL) with the conventional diamond tubular lattice (DTL). Our results show that the ductility of ATL increases by 72.7% compared with that of the DTL structure. The finite element simulations reveal that the stress is more uniformly spread on the sinusoidal ligaments for ATL, while rather concentrated on the joints of straight ligaments for DTL. This phenomenon is intrinsically due to the bending of sinusoidal ligaments along both radial and axial directions, while straight beams bend mainly along the radial direction. We then investigated the effects of the geometrical parameters of the sinusoidal ligament on radial mechanical performance. Experimental results indicate that the beam depth h/l has the most significant effect on the stiffness and peak load. The stiffness and maximum load surge by 789% and 1131%, respectively, when h/l increases from 0.15 to 0.30. In contrast, the beam amplitude A/l has a minor effect on the stiffness and peak load compared to beam depth and beam thickness. However, increasing the amplitude of the sinusoidal ligament can enlarge the ductility strikingly. The ductility can increase by 67.5% if the amplitude is augmented from A/l=0.1 to A/l=0.35. The findings from this work can provide guidance for designing more mechanically robust stents for medical engineering

Modelling of Failure Behaviour of 3D-Printed Composite Parts

Failure in 3D-printed composite parts is complex due to anisotropic properties, which are mainly governed by printing parameters, printing strategy, and materials. Understanding the failure behaviour of materials is crucial for the design calculations of parts. Effective computational methodologies are yet not available for accurately capturing the failure behaviour of 3D-printed parts. Therefore, we proposed two different computational methodologies for modelling the failure behaviour of 3D-printed parts. 3D-printed parts subjected to uniaxial tensile loading were considered for modelling. In the first method, the computational model employed nonlinear properties of virgin material, and the model predicted higher values than the experimental results. This method provided idealistic nonlinear behaviour of 3D-printed parts. The difference in the results of experimental and computational is significant, especially in the case of 3D-printed composites. In the second method, the computational model utilized nonlinear material data from mechanical testing results and the model predicted accurate nonlinear behaviour of 3D-printed parts. This method provided realistic material behaviour of 3D-printed parts. Therefore, for effective design and analysis, it is suggested to use the latter computational methodology to capture the failure behaviour of 3D-printed parts accurately

Effect of Post Processing Heat Treatment Routes on Microstructure and Mechanical Property Evolution of Haynes 282 Ni-Based Superalloy Fabricated with Selective Laser Melting (SLM)

Selective laser melting (SLM) is one of the most widely used additive manufacturing technologies. Fabricating nickel-based superalloys with SLM has garnered significant interest from the industry and the research community alike due to the excellent high temperature properties and thermal stability exhibited by the alloys. Haynes-282 alloy, a γ′-phase strengthened Ni-based superalloy, has shown good high temperature mechanical properties comparable to alloys like R-41, Waspaloy, and 263 alloy but with better fabricability. A study and comparison of the effect of different heat-treatment routes on microstructure and mechanical property evolution of Haynes-282 fabricated with SLM is lacking in the literature. Hence, in this manuscript, a thorough investigation of microstructure and mechanical properties after a three-step heat treatment and hot isostatic pressing (HIP) has been conducted. In-situ heat-treatment experiments were conducted in a transmission electron microscopy (TEM) to study γ′ precipitate evolution. γ′ precipitation was found to start at 950 °C during in-situ heat-treatment. Insights from the in-situ heat-treatment were used to decide the aging heat-treatment for the alloy. The three-step heat-treatment was found to increase yield strength (YS) and ultimate tensile strength (UTS). HIP process enabled γ′ precipitation and recrystallization of grains of the as-printed samples in one single step

Printability studies of Ti-6Al-4V by metal fused filament fabrication (MF3)

Predicting the influence of material composition on the printability of highly filled metal powder-polymer systems present a significant challenge in metal fused filament fabrication (MF3). The current work presents an approach to evaluate new material compositions used to fabricate filaments for their printability. In this study, filaments with 59 vol.% (87 wt.%) of Ti-6Al-4V powder with two particle size distributions {fine (D-50 = 13 mu m) and coarse (D-50 = 30 mu m)} dispersed in a polymer matrix were examined. The respective forces to overcome the pressure drop, for successful printing, were found to increase with an increase in the feed rate, and were also dependent on the feedstock viscosity. In addition, shear forces estimated from the filament shear strength were found to be limiting conditions for successful printing. Based on these observations, a criterion has been proposed to evaluate filament printability from the predicted limiting force for filament failure and the required force to achieve continuous material flow for successful printing. Under present experimental conditions, successful printing was achieved up to 2 mm/s and 8 mm/s for fine and coarse powder filaments, in good agreement with the model predictions. The model was experimentally tested and found to be applicable for other compositions. The results demonstrate a new printability criterion to design novel materials for MF3