Mechanical Properties Of Parts Research Articles

Grain growth prediction in selective electron beam melting of Ti-6Al-4V with a cellular automaton method

An integrated modeling framework coupling the discrete element method for powder spreading, finite volume method for powder bed melting, and an extended cellular automaton method for grain structure evolution during solidification is proposed. In this framework, the initial grain structure of both the substrate and metal powders can be taken into account and used to capture epitaxial and competitive grain growth. The framework is used to provide an in-depth understanding of microstructure development in Ti-6Al-4V during the selective electron beam melting process. The complex process of grain growth during deposition of multiple tracks and multiple layers is modeled through an analysis restarting scheme. The epitaxial growth of grains from pre-existing grains, in particular the grains of partially melted powders, is reproduced. The mechanism of microstructure development within the overlap region of consecutive tracks and layers for various scan strategies is revealed. The simulation results are in qualitative agreement with experimental observation in the literature. The proposed modeling framework is a powerful tool to guide optimal process parameters that lead to designed, site-specific microstructure control and therefore to tailored mechanical properties of parts fabricated by the powder bed fusion additive manufacturing process.

New Grain Formation by Constitutional Undercooling Due to Remelting of Segregated Microstructures during Powder Bed Fusion.

A microstructure has significant influence on the mechanical properties of parts. For isotropic properties, the formation of equiaxed microstructures by the nucleation of new grains during solidification is necessary. For conventional solidification processes, nucleation is well-understood. Regarding powder bed fusion, the repeated remelting of previous layers can cause nucleation under some conditions that are not explainable with classical theories. Here, we investigate this nucleation mechanism with an unprecedented level of detail. In the first step, we built samples with single crystalline microstructures from Ni-base superalloy IN718 by selective electron beam melting. In the second step, single lines with different parameters were molten on top of these samples. We observed a huge number of new grains by nucleation at the melt-pool border of these single lines. However, new grains can only prevail if the alignment of their crystallographic orientation with respect to the local temperature gradient is superior to that of the base material. The current hypothesis is that nucleation at the melt-pool border happens due to remelting microsegregations from former solidification processes leading to constitutional undercooling directly at the onset of solidification. This study offers the opportunity to understand and exploit this mechanism for different manufacturing processes.

Additive manufacturing of non-planar layers with variable layer height

Abstract The freedom and potential gained by creating objects layer-by-layer using additive manufacturing technologies is offset by the limitations the 2.5D process holds. Currently, surface quality and mechanical properties of parts are limited by path planning algorithms. This study presents an algorithm for non-planar path planning with variable layer height, enabling the accurate representation of freeform surfaces and introducing the potential for increasing the parts’ mechanical properties by tailoring the layers to the load-case. By using mathematical functions to describe non-planar layers and calculating the amount of material to be extruded, layer thickness may vary inside the same layer, enabling transitions between different curved layers without introducing air gaps. In addition, means for selecting a beneficial nozzle geometry for non-planar additive manufacturing are presented. Finally, manufactured parts are evaluated, showing the benefits of the presented method. Specifically, it is shown that surface roughness can be reduced by 76% for curved top surfaces and indications for improved mechanical properties can be derived from performed tests.

Impact of sintering time and temperature on mechanical properties in projection sintering of Polyamide-12

Abstract In powder bed fusion additive manufacturing (AM), the fusing process is temperature and time dependent. However, little work has been done to understand how different processing temperatures and times might impact the mechanical properties at longer sintering times than are typical in laser sintering (LS) systems. Prior results with projection sintering have shown that heating for longer times (>1 s) improves part toughness compared to laser sintering. In this work, Large Area Projection Sintering (LAPS) is used to sinter entire layers of material simultaneously over the course of a few seconds with spatial control of layer temperature. This work evaluates the effect of time and temperature on the mechanical properties of parts sintered from PA 2202 (Polyamide 12) powder. Toughness is shown to increase significantly with longer sintering times (5–8 s) and higher temperatures (195–205 °C) with elongations at break (EaB) over 100% and strengths of up to 51.7 MPa. This represents a small increase in strength and an order of magnitude increase in elongation at break relative to LS datasheet values for the material. Peak mechanical properties are achieved sintering at lower temperature (195 °C) and longer times (5–8 s). The density of the samples that maximize toughness and strength is greater than 1.02 g/cm3 compared to datasheet values of 0.98 g/cm3. Porosity elimination could be a mechanism for improved performance though it does not fully explain the improvements in strength and ductility.

Investigation of the Mechanical Properties of Parts Fabricated with Ultrasonic Micro Injection Molding Process Using Polypropylene Recycled Material.

This research focuses on investigating how physical and mechanical properties of polypropylene (PP) recycled material are modified when ultrasonic micro injection molding (UMIM) technology is used to produce material specimens. Experimental characterization by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), Fourier transform infrared (FTIR) spectra, and rheology tests show that the fabricated PP samples were able to withstand up to five times recycled processing before some signs of mechanical and physical properties degradation are observed. Surprisingly, uniaxial extension tests show an increase of 3.07%, 10.97% and 27.33% for Young’s modulus, yield stress and ultimate stress values, respectively, and a slight reduction of 1.29% for the samples elongation at break when compared to the experimental data collected from virgin material samples. The improvement of these mechanical properties in the recycled samples suggests that ultrasonic microinjection produces a mechano-chemical material change.

Comparative analysis of structure and mechanical properties of parts produced by electron-beam additive manufacturing and cold metal transfer

Currently, the most prospective industry development areas are prototyping and additive manufacturing. In contrast to more precise powder technologies, faster wire technologies providing non-porous products are of great interest. This paper contains a comparative analysis of the effect of two wire technologies – electron-beam additive manufacturing and cold metal transfer – on the structure and mechanical properties of Aluminum Alloy 5056. Electron beam power is close to arc power at optimal printing parameters, but cold metal transfer is cheaper due to the impulse nature of the arc. In addition, the arc method is implemented in an argon atmosphere, and this accelerates the applied layer cooling. In general, the grain structure of the material is refined due to the lower heat transfer and accelerated cooling. This results in increased strength and microhardness. The constant heat removal from the substrate and the increase in the product weight change thermal conditions of the following layer. This is controlled by beam/arc powder reduction, but each layer has its own thermal history affecting the structure and properties. In particular, the more heat is transferred to the layer from the previous layers, the less strong it is. When a certain height (about 30 mm) is passed, cooling is intensified by the large mass of the product and the strength is increased again. This is most characteristic for cold metal transfer. However, these fluctuations are rather small. Mechanical properties along the growth direction are highly stable in both technologies. Cold metal transfer also shows less alloying magnesium burn-off. In general, currently the cold metal transfer technology is more cost effective and provides better quality products.

Design and verification of enhanced CFRTPCs fabrication technique using fused deposition modeling

Research shows that mechanical properties of parts produced using fused deposition modeling (FDM) are inferior when compared to parts produced using conventional techniques such as injection molding. Efforts have been made in recent years to improve mechanical properties by reinforcing the parts with high strength fibers. This has been achieved by either modifying FDM setups to extrude fibers with thermoplastics and fabricate continuous fiber reinforced thermoplastic composites (CFRTPCs) or employing manual techniques subsequent to part production. Existing CFRTPCs fabrication procedures have limitations of fiber exposure to environment, no direct control method for volume fraction, and poor surface finish. This research work is focused on improving the process of producing CFRTPCs by addressing these limitations using a dual extruder FDM setup. The process developed was tested for its feasibility using Kevlar fiber as reinforcement for commercially available ABS, PLA, PLA-C, and PLA-Cu thermoplastic fibers. Taguchi L16 orthogonal array was used to design experiments, while tensile and flexural testing was performed to determine mechanical properties achieved. Tensile strength was improved up to 3 times the baseline value of thermoplastics, while flexural strength was improved up to 1.6 times. This technique can further the goal of developing CFRTPCs, on industrial level, using FDM with better control over volume fraction and fiber layup.

Mechanical Properties of 3D Printed Polylactic Acid Product for Various Infill Design Parameters: A Review

3D printing is widely used for various applications as it offers many benefits. The mechanical property of the part manufactured by using 3D printing is very critical. For that reason, it is important to understand how different values of 3D printing process parameters impact the mechanical properties of the part. As Polylactic Acid (PLA) is most widely used as 3D printing material, it is chosen as the material discussed in this research. The purpose of this research is to provide information related to the influence of various parameters of 3D printing to the mechanical properties of the PLA part. A literature review was performed based on the current research that investigates the 3D printing process of PLA. Based on the literature review, the infill design parameters are considered as important parameters and discussed in this research. The infill design parameters referred in this research are layer thickness, infill pattern, infill density, infill width, and infill deposition speed. The mechanical properties discussed in this research are tensile strength and yield strength, ductility, elasticity or young modulus, compression strength, flexural strength, and stiffness.

EFFECT OF INFILL PARAMETERS ON MECHANICAL PROPERTIES IN ADDITIVE MANUFACTURING

The purpose of this paper is to study and outline the effects of infill parameters (percentage and pattern) using fused deposition manufacturing on mechanical properties of PLA printed samples. Three infill patterns were tested (rectilinear, honeycomb and Hilbert curve) while infill percentage was tested at three levels (20, 60 and 90 per cent). The properties examined were tensile strength, tensile modulus, elongation, Charpy impact test, morphology of the fractures of tensile and impact test and thermo mechanical analysis. Also, a thermal analysis was done using differential scanning calorimetry to the raw polymer in order to determine the processing temperature. Results showed the influence of the filling parameters in 3D printing on the mechanical properties of the obtained part. The filling pattern greatly influences the mechanical properties of parts with low filling percentages. Honeycomb filling pattern is the one with better mechanical results. The complexity of the filling pattern influences on the processing time. Nozzle direction changes in complex patterns lengthen processing time. Results can significantly influence custom design and manufacturing of parts using material fused deposition modeling.

Improvement of Microcathode Arc Thruster Lifetime by Deposition of Boron-Containing Coating

Boron-containing coatings are actively used to improve the surface properties of mechanical parts of various devices and cutting tools. In this Paper, we demonstrate that deposition of boron-containing coatings by direct electron-beam evaporation of a boron target with a fore-vacuum plasma-cathode electron source can be used to substantially (by a factor of approximately 6–17) improve the lifetime of miniature (centimeter-sized), low-power (several watts), micronewton thrust level microcathode arc thrusters. Such improvement is a result of slowing down the interelectrode film degradation that occurs after numerous arc pulses. This improvement is observed after applying a hard (resistant to shock by plasma in a single pulse) sputter-resistant (able to maintain its protective properties for numerous pulses) boron coating on the interelectrode dielectric (alumina ceramic). This finding opens up a new way to improve the performance and lifetime of low-power vacuum-arc based propulsion devices for small satellites.

Effect of Material Segregations Due to Squeeze Parameters on Mechanical Properties of High Pressure Diecast Parts

Abstract This article is a research on the effect of material segregations due to squeeze parameters on mechanical properties of high pressure die cast parts. The technology of squeezing is applied in high pressure die casting technology with the aim to improve the internal material health of the castings from aluminium alloys, such as AlSi9Cu3(Fe), components incorporated in assemblies as mechanical and hydraulic parts. The objective of this article is to determinate the influence of the secondary effects of squeeze technology on the mechanical properties of parts produced from AlSi9Cu3(Fe) alloys, with HPDC technology.

Optimization of the Sintering Parameters for Materials Manufactured by Powder Injection Molding

The properties of sintered and heat-treated steels produced from the Catamold 8740 material by powder injection molding were examined. Parts made of the Catamold 8740 low-alloy mild carbon steel are used in the military, automotive, and other industries where high reliability and resistance to dynamic loads are required. The Catamold 8740 chemical homogeneity was studied as a function of powder injection molding parameters: heating rate, sintering temperature, holding time, and subsequent heat treatment. Microscopic analysis showed that Catamold 8740 was a mechanical mixture of powders in various sizes (carbonyl iron, nickel, Fe–Mo, Fe–Cr, Fe–Si-Mo, Fe–Si). When the heating rate of the Catamold 8740 powder mixture increased from 2 to 5 °C/min, the microstructural heterogeneity caused by uneven compaction decreased and the alloy formation process activated at 900–1340°C. The impact strength of Charpy V-notch test samples changed from 10.39 to 11.52 J/cm2 with higher sintering temperature and heating rate increasing from 2 °C/min (1270°C) to 5 °C/min (1340°C). When holding time increased from 30 to 90 min at a sintering temperature of 1340°C, the material became denser, the pores rounded, and the ferrite matrix homogeneous. However, the impact strength decreased by a factor of 1.4 because of coarser grain sizes and brittle fracture. Heat treatment processes reduced the impact strength after sintering. The results obtained were used to optimize the powder injection molding parameters. The influence of chemical and dimensional inhomogeneity of the starting Catamold 8740 powders and sintering kinetics on the structure and mechanical properties of parts operating under impact loads was established.

Effects of laser shock peening on microstructure and fatigue behavior of Ti–6Al–4V alloy fabricated via electron beam melting

Laser shock peening (LSP) is a post-treatment process that is widely used to modify the surface microstructure and mechanical properties of parts constructed by additive manufacturing (AM). In this study, the influence of LSP on the microstructure and fatigue behavior of Ti–6Al–4V alloy manufactured via electron beam melting (EBM), a popular method of AM, was investigated. The microstructure of the EBM sample consisted of the β phase (~6 vol%) and α lamellar phase. Grain refinement of the α phase occurred via both dislocation evolution and deformation twinning during LSP. A theoretical description of the microstructural evolution, particularly the distribution of deformation twins, was developed. The fatigue strength and micro-hardness of the EBM samples increased by approximately 17% and 11% after LSP treatment, respectively. The fatigue fracture morphologies at three defined damage stages (crack initiation, crack propagation, and instantaneous rupture) were examined for EBM samples before and after LSP. The dominant mechanism of fatigue strength enhancement by LSP was discussed. The effects of residual compressive stress assistant with adiabatic temperature increase and grain refinement of the α phase produced by LSP reduced the pre-existing crack size, suppressed crack initiation, and increased the required work for fatigue fracture.

Mechanical Properties of Duplex Treated Steels Obtained by Instrumented Indentation

Nowadays there is a growing need to reduce or control wear, corrosion and fatigue in order to extend the lifetime of mechanical parts, to make engines and devices more efficient, to develop new advanced products, to conserve material resources, to save energy and to improve the safety. The surface properties of mechanical parts may be improved through Duplex treatments. A Duplex treatment is a sequence of two treatments, combining their advantages and leading to better surface properties. A Duplex treatment consisting in nitriding and work hardening through shot peening has been chosen as a solution for improving the properties of EN 34CrNiMo6 alloyed steel. This paper reports the results obtained for hardness and bulk modulus on treated and untreated samples. The samples were examined using a Dynamic Ultra Micro Hardness (DUH) tester under a set of maximum loads ranging from 100 to 1000 mN. Each sample was subjected to load-unload cycle under the same amount of maximum load and the loads vs. penetration depth curves were plotted. Results showed a better mechanical behavior of Duplex treated.

Thermal and geometry impacts on the structure and mechanical properties of part produced by polymer additive manufacturing

AbstractA relatively new additive manufacturing machine called Freeformer was employed as an alternative to common Fused Filament Fabrication (FFF) machines. While FFF machines are fed with expensive and few commercially available filament feedstock, Freeformer is fed with cheap and common polymer pellets. In this study, more than 400 dumbbells made of Acrylonitrile Butadiene Styrene (ABS) were processed varying many processing conditions to evaluate their impacts on the structure and so on, the mechanical properties of 3D parts. Among processing parameter, nozzle temperature, manufacturing chamber temperature, discharge parameters, filling density, raster geometry, slicing distance, number of contour lines, processing speed, filling raster‐contour lines overlap, and processing angles were studied. Images obtained with a scanning electron microscope and 3D part density estimations reveal strong changes on the 3D part structure as a function of the processing parameters so that tensile tests exhibit high variations between the 3D part mechanical properties.

Microstructure and mechanical properties of Cu-modified AlSi10Mg fabricated by Laser-Powder Bed Fusion

This influence of surface modification of powder feedstocks for additive manufacturing is assessed. Commercial AlSi10Mg powder was coated with 1 wt% copper using a copper formate precursor, which was reduced to metallic copper after vacuum heat treatment. Consolidated samples were produced using Laser-Powder Bed Fusion (L-PBF). Both the untreated and coated powders produced materials which exhibited high preferential crystal orientation, with grains aligned parallel to the build direction. The microstructure of the consolidated materials was characterized by SEM and TEM. The cells consisted of a α-Al matrix with copper particles decorating the intercellular region and eutectic silicon homogeneously dispersed in the cell boundary. The effect of the T6 heat treatment on the mechanical properties of the L-PBF-processed materials was a decrease in the strength. The specimens fabricated from coated powder exhibited an increased ultimate tensile strength (461 ± 0.2 MPa) and 12% elongation at break compared to the AlSi10Mg parts (346 ± 1.0 MPa) and 10% elongation. The study establishes the feasibility of modifying the composition of L-PBF-processed materials via the coating of powder feedstocks and that the coating additions can be exploited to enhance mechanical properties of parts after heat treatment.

Effect of extrusion temperature on fused filament fabrication parts orthotropic behaviour

PurposeThe purpose of this paper is to verify the effects of extrusion temperature on orthotropic behaviour of the mechanical properties of parts obtained by fused filament fabrication (FFF) under quasi-static tensile loads.Design/methodology/approachTensile tests were performed on single layer specimens fabricated in polylactic acid (PLA) and acrylonitrile butadiene styrene (ABS) to evaluate the mechanical properties at different extrusion temperatures and raster orientations (0°, 45° and 90°). Furthermore, a detailed study of morphological characteristics of the single layer samples cross-section and of the bonding quality among adjacent deposited filaments was performed by scanning electron microscopy to correlate the morphology of materials with mechanical behaviour.FindingsThe results show that the orthotropic behaviour of FFF-printed parts tends to reduce, while the mechanical properties improved with increase in extrusion temperature. Furthermore, the increase in extrusion temperature led to an improvement in inter-raster bonding quality and in the compactness and homogeneity of the parts.Originality/valueThe relation between the extrusion temperature, orthotropic behaviour and morphological surface characteristics of the single layer specimen obtained by FFF has not been previously reported.

Selective laser sintering and post-processing of sisal fiber/ poly-(ether sulfone) composite powder

Selective Laser Sintering (SLS) technology can be utilized to recycle residues from forestry and agriculture, thereby alleviating shortages of materials and reducing energy consumption by producing wood-plastic pieces for industrial application. The mechanical strength of wood-plastic SLS parts is low, which restricts the application of this technology. In this study, a novel type of sisal fiber/poly-(ether sulfone) (PES) composite was prepared using a polymer mixing method in order to improve the mechanical properties of SLS parts. Single-layer sintering method was adopted to determine the proper processing parameters. The mechanical properties of the parts with different ingredient ratios and different particle sizes of sisal fiber before and after post-processing were tested using a universal testing machine. The morphology was examined using scanning electron microscopy (SEM). Results showed that the mechanical properties of the printed parts were relatively enhanced; when the mixing ratio of composite powder was 10/90 wt/wt. In addition, the part fabricated by powder of particles size less than 0.105 mm (0.125 mm ≥ PS < 0.105mm) had the best mechanical strength. Moreover, the post-wax treatment significantly improved the strength of the parts, and the surfaces became smoother.

Impact of process parameters on mechanical behaviour in multi-material jetting

PolyJet material jetting is a rapidly growing Additive Manufacturing (AM) technology due to its ability to build precise multi material parts having complex geometries. Mechanical properties of parts fabricated by AM are affected by printing parameters. Examining the strength of AM parts is important, due to the differences with PolyJet technology. The aim of this study is to characterize the effect of process parameters on the mechanical properties of VeroClear and VeroWhitePlus test specimens manufactured with digital material printing mode. Tensile, flexural and shore hardness tests are carried out to determine the mechanical properties of the 3D printed specimens. Findings indicate that the specimens printed in glossy finish are stronger and stiffer than matte finish. From a view of material and material concentration, VeroClear specimens show better results when compared to the mechanical properties of VeroWhitePlus specimens. In addition, comparison between the material consumptions and required printing time to complete the specimens were also carried out. All these test results revealed, VeroClear with glossy finish specimen is more efficient than the other combinations as it is significantly improved. This work provides a selection guideline that can be used to increase the durability of functional parts in wide variety of applications.

On the effect of shielding gas flow on porosity and melt pool geometry in laser powder bed fusion additive manufacturing

Metal additive manufacturing is moving from rapid prototyping to on-demand manufacturing and even to serial production. Consistent part quality and development of a wider range of available materials are key for wider adoption. This requires control and optimization of various laser and scanning parameters. Therefore, process modeling has been extensively pursued to reduce experimental runs in the search for parameters that produce dense, high-quality parts for the given alloy. However, these optimal parameters remain machine-specific if conditions defined by the machine architecture are not considered. Previous studies have shown that shielding gas flow is one such parameter that affects porosity and mechanical properties of parts produced with laser powder bed fusion. However, a lack of consensus remains regarding which phenomena are responsible for the observed decrease in quality. In this study, the effect of shielding gas flow velocity on porosity and melt pool geometry in laser powder bed fusion additive manufacturing is studied. It is shown that decreasing the gas flow velocity leads to a drastic loss of penetration of single scan tracks, leading to increased lack-of-fusion porosity at the part level. This is attributed to the obstruction of the laser beam by the process-induced vapor plume emissions of the individual tracks being scanned. As the vapor plume, and how effectively it is removed by the shielding gas flow, have a significant effect on the melt pool geometry in laser powder bed fusion, models aiming at predicting the melt pool geometry and attempts to transfer process parameters from one machine to another should consider the effect of the shielding gas flow.