29 research outputs found
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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
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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
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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
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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
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The Effect of Nanoparticle Addition on SiC and AlN Powder-Polymer Mixtures: Part I. Packing & Flow Behavior
The development of methods to increase sintered density and improve dimensional tolerances is
a crucial issue in powder metallurgy and ceramic processing. Increasing the packing density of
starting powders is one effective route to achieve high sintered density and dimensional
precision. The current paper presents an in-depth study on the effect of nanoparticle addition on
the powder content of SiC and AlN powder-polymer mixtures. In particular, bimodal mixtures of
nanoscale and sub-micrometer particles were found to have significantly increased powder
volume fraction (solids loading) in the mixtures for injection molding. This observation to
increasing packing density by using nanoparticles is surprising and novel since nanoparticles are
known to inherently exhibit poor packing behavior. Additionally, for a given volume fraction of
powder, the bimodal μ-n suspensions had a lower viscosity at any shear rate compared to the
monomodal μ- suspensions. The ability to lower the suspension viscosity by adding
nanoparticles to micron-sized particles has important implications for processing of particulate
suspensions by powder injection molding (PIM), extrusion, slip casting and tape casting.
Samples made from bimodal powders exhibited slower polymer removal during debinding and
higher densification with lower shrinkage on sintering compared to the corresponding samples
made from monomodal powder mixtures.Keywords: Rheology, Packing fraction, Aluminum nitride, Nanoparticles, Silicon carbide, Bimodal mixturesKeywords: Rheology, Packing fraction, Aluminum nitride, Nanoparticles, Silicon carbide, Bimodal mixture
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
Estimating Powder-Polymer Material Properties Used in Design for Metal Fused Filament Fabrication (DfMF(3))
Metal fused filament fabrication (MF3) combines fused filament fabrication and sintering processes to fabricate complex metal components. In MF3, powder-polymer mixtures are printed to produce green parts that are subsequently debound and sintered. In the design for MF3 (DfMF(3)), it is important to understand how material properties of the filament affect processability, part quality, and ensuing properties. However, the materials property database of powder-polymer materials to perform DfMF(3) simulations is very limited, and experimental measurements can be expensive and time-consuming. This work investigates models that can predict the powder-polymer material properties that are required as input parameters for simulating the MF3 using the Digimat-AM process design platform for fused filament fabrication. Ti-6Al-4V alloy (56-60 vol.%) and a multicomponent polymer binder were used to predict properties such as density, specific heat, thermal conductivity, Young's modulus, and viscosity. The estimated material properties were used to conduct DfMF(3) simulations to understand material-processing-geometry interactions
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
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 3~4% 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