Additive manufactured A357.0 samples using the laser powder bed fusion technique: Shear and tensile performance

New aluminium alloys, with lower silicon content than in the first-developed formulations, have recently been introduced in the field of Additive Manufacturing and are dedicated to automotive applications. As they are relatively new, mechanical characterization under standard protocols of the automotive field are of utmost scientific as well as industrial relevance. The paper addresses the mechanical properties and microstructure of A357.0. Static tensile and shear tests of samples built by Laser Powder Bed Fusion, with different orientations in the machine work volume, have been performed. The aim was to identify possible anisotropy in the tensile and shear behaviour of this innovative alloy. Particularly for shear, the effect of adhesion between the layers onto shear strength was studied. Results analysis, by means of statistical tools, allows for the affirmation that no tensile modulus or yield strength anisotropy is observed. Instead, a small (yet statistically significant) increase in both shear-and tensile strength and a decrease in ductility are obtained as the direction of the specimens approaches the growth direction. Scanning Electron Microscope (SEM) observation of the failure mechanisms assisted in the interpretation of the results, by relating different failure modes to the relative orientation of loads versus the directions of inherent anisotropy in Laser Powder Bed Fusion processes

Comparative study of three yttria-stabilized zirconia formulations in colored vs natural shades

Recently the attention in the field of fixed dental restorations has focused on structural ceramics. Yttria-stabilized tetragonal zirconia (Y-TZP) is proposed as an alternative to conventional ceramic-metal prostheses, since it merges excellent aesthetic quality with outstanding toughness. Before Y-TZP integral structures spread in dental practice, much needs to be studied as regards the mechanical response, the influence of color and of the manufacturing process, the occurrence of aging phenomena. This work aims at a comparative study of three Y-TZP commercial formulations in five shades; the variations introduced by polishing and their recovery after annealing are also addressed. Flexural strength and microhardness are investigated, basing on international standards. Significant differences between the groups and parts' reliability are evaluated through statistical data processing and Weibull analysis. Results show low flexural strength (500-800MPa), at least 45% inferior to technical specifications, and low Weibull modulus. Hardness is instead higher than expected (1500-1700 HV1). The main finding of the research is that the effect of color on mechanical properties is significant in many cases, hence esthetical requirements must be merged with mechanical ones. Y-TZP shows an extreme variability with manufacturing conditions, so nominal characteristics should be assumed with caution and higher reliability is still required

GAS AND REFRIGERANT ASSISTED INJECTION MOULDING PROCESS

Assisted Injection Moulding (AIM) is part of a family of technologies that are conducted with plastic processing methods to improve product quality and significantly reduce costs. These technologies include the injection of gas or water, at high pressure, into the molten polymer within the injection mould. This process cores out sections of the part, and leaves hollow areas. The fluid-assisted injection moulding technology, which includes gas-assisted moulding and water-assisted moulding, has been used widely to manufacture plastic parts in recent years, due to the achievement of lightweight products, the relatively low resin cost per part, the fast cycle time, the uniform distribution of the packing pressure and the elimination of sink marks. Gasassist and water-assist technology may also be combined in sequence to achieve other benefits in certain applications. The basic idea of the proposed process is that the evaporation of a small quantity of water leads to a notable decrease in the cooling time and an increase in the dimensional tolerance of the injected part. Even though several patents pertaining to the use of gas and a refrigerant to obtain a hollow component exist, there is still a lack of knowledge regarding the effectiveness of the process. The present research has evaluated the effect of a co-injection of micro quantitates of water together with nitrogen

Evaluation of Performance of Cast and Laser-Sintered cr-co Alloys for Dental Applications

Dental prostheses may be built by additive layer manufacturing, specifically by direct metal laser sintering (DMLS). This innovative process allows a high percentage of unmanned work and the direct fabrication of parts from CAD data. Even if , in the product and production development field, these techniques are studied since last ’80, up today there is a lack of knowledge about mechanical performance in the medical application. The target of this paper is to investigate the mechanical and functional characteristics, with respect to traditional cast parts. Tensile specimens were built in accordance with ASTM E8M both by DMLS (EOSINT-M270 ) and traditional lost-wax casting, using the same Cr-Co alloy. An experimental plan was designed to evaluate the effect of all process phases. Tensile performances, hardness, roughness and dimensional measurement, rupture surfaces SEM observation and porosity evaluation were performed .Sintered parts are rougher and proved to have Rockwell hardness values higher confront to cast ones. No significant dimensional variations were noticed among different processes. Some of the cast specimens present defects (macro porosity) that are absent in the sintered ones.UTS of all sintered specimens (~1400MPa) is almost double than of cast ones, whereas are more fragile (εb~5 vs 20%). The porosity in zone free of defects are comparable. Cr-Co specimen produced by DMLS show excellent strength and absence of defects with respect to traditional casting. Low εb values are not critical, since deformation of the final prostheses is limited by the ceramic layer fragility

Evaluation of Laser-Sintered CR-CO and TI Alloys for Dental Applications

Even if additive layer manufacturing techniques have been introduced in industries since last \u201980, the application in medicine is quite recent and tend to remain at research level. In dental implantology the introduction of these technologies in the prostheses production could introduce more precision well time and money savings. Dental prostheses may be built by additive layer manufacturing, specifically by direct metal laser sintering (DMLS). The target of this paper is to investigate the mechanical and microstructural characteristics, comparing samples built along different orientation. Tensile specimens were built in accordance with ASTM E8M both by DMLS (EOSINT-M270 ), using Cr-Co alloy and Ti6Al4V alloy. An experimental plan was designed to evaluate the effect of different built orientation. Density, hardness, tensile performances, rupture surfaces SEM observation, porosity evaluation and microstructure observation were performed on the following group of specimens (4 specimen for each group): were produced (4 for each group) in three orientations with respect to the machine distinctive directions Both alloys have good mechanical performance in terms of tensile strength, elongation and hardness. The specimens revealed a low porosity and of consequence to be quite fully densified. The microstructure observed is very fine and explain the mechanical characteristics of the materials. The statistic analysis doesn\u2019t evidence a unique difference between the different building orientation. DMLS produce parts with excellent mechanical properties independently from building orientation

Multi-disciplinary approach in engineering education: learning with additive manufacturing and reverse engineering

Purpose - The purpose of this paper is to report an interdisciplinary, cooperative-learning project in a second-year course within the "Enzo Ferrari" Master of Science Degree in Mechanical Engineering. The work aims to raise awareness of the educational impact of additive manufacturing and reverse engineering. Design/methodology/approach - Students are asked to develop, concurrently, the design and the manufacturing solution for an eye-tracker head mount. A digital head model is reverse engineered from an anatomical mannequin and used as an ergonomic mock-up. The project includes prototype testing and cost analysis. The device is produced using additive manufacturing techniques for hands-on evaluation by the students. Findings - Results of the presented case study substantiate the authors' belief in the tremendous potential of interdisciplinary project-based learning, relying on innovative technologies to encourage collaboration, motivation and dynamism. Originality/value - The paper confirms a spreading conviction that the soon-to-be engineers will need new practice-oriented capabilities to cope with new competitive scenarios. Engineering education must adapt to the social, rather than industrial, revolution that is being brought about by additive fabrication

Fatigue behavior of as-built L-PBF A357.0 parts

Laser-based powder bed fusion (L-PBF) is nowadays the preeminent additive manufacturing (AM) technique to produce metal parts. Nonetheless, relatively few metal powders are currently available for industrial L-PBF, especially if aluminum-based feedstocks are involved. In order to fill the existing gap, A357.0 (also known as A357 or A13570) powders are here processed by L-PBF and, for the first time, the fatigue behavior is investigated in the as-built state to verify the net-shaping potentiality of AM. Both the low-cycle and high-cycle fatigue areas are analyzed to draw the complete Wohler diagram. The infinite lifetime limit is set to 2 7 106stress cycles and the staircase method is applied to calculate a mean fatigue strength of 60 MPa. This value is slightly lower but still comparable to the published data for AlSi10Mg parts manufactured by L-PBF, even if the A357.0 samples considered here have not received any post-processing treatment

Effects of build orientation and element partitioning on microstructure and mechanical properties of biomedical Ti-6Al-4V alloy produced by laser sintering

Direct Metal Laser Sintering (DMLS) technology was used to produce tensile and flexural samples based on the Ti-6Al-4V biomedical composition. Tensile samples were produced in three different orientations in order to investigate the effect of building direction on the mechanical behavior. On the other hand, flexural samples were submitted to thermal treatments to simulate the firing cycle commonly used to veneer metallic devices with ceramics in dental applications. Roughness and hardness measurements as well as tensile and flexural mechanical tests were performed to study the mechanical response of the alloy while X-ray diffraction (XRD), electron microscopy (SEM, TEM, STEM) techniques and microanalysis (EDX) were used to investigate sample microstructure. Results evidenced a difference in the mechanical response of tensile samples built in orthogonal directions. In terms of microstructure, samples not submitted to the firing cycle show a single phase acicular α’ (hcp) structure typical of metal parts subject to high cooling rates. After the firing cycle, samples show a reduction of hardness and strength due to the formation of laths of the β (bcc) phase at the boundaries of the primary formed α’ plates as well as to lattice parameters variation of the hcp phase. Element partitioning during the firing cycle gives rise to high concentration of V atoms (up to 20 wt%) at the plate boundaries where the β phase preferentially forms