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2 pages, 139 KiB

Open AccessEditorial

Additive Manufacturing (AM) of Metallic Alloys

by Flaviana Calignano

Crystals 2020, 10(8), 704; https://doi.org/10.3390/cryst10080704 - 15 Aug 2020

Cited by 2 | Viewed by 1683

Abstract

The introduction of metal additive manufacturing (AM) processes in industrial sectors, such as the aerospace, automotive, defense, jewelry, medical and tool-making fields, has led to a significant reduction in waste material and in the lead times of the components, innovative designs with higher [...] Read more.

The introduction of metal additive manufacturing (AM) processes in industrial sectors, such as the aerospace, automotive, defense, jewelry, medical and tool-making fields, has led to a significant reduction in waste material and in the lead times of the components, innovative designs with higher strength, lower weight and fewer potential failure points from joining features [...] Full article

(This article belongs to the Special Issue Additive Manufacturing (AM) of Metallic Alloys)

Research

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11 pages, 6479 KiB

Open AccessArticle

Microstructure and Mechanical Properties of Tempered Ausrolled Nanobainite Steel

by Jing Zhao, Dezheng Liu, Yan Li, Yongsheng Yang, Tiansheng Wang and Qian Zhou

Crystals 2020, 10(7), 573; https://doi.org/10.3390/cryst10070573 - 03 Jul 2020

Cited by 3 | Viewed by 1834

Abstract

The microstructures and mechanical properties of ausrolled nanobainite steel, after being tempered at temperatures in the range of 200−400 °C, were investigated in this study. After being tempered, bainitic ferrite is coarsened and the volume fraction of retained austenite is reduced. The hardness [...] Read more.

The microstructures and mechanical properties of ausrolled nanobainite steel, after being tempered at temperatures in the range of 200−400 °C, were investigated in this study. After being tempered, bainitic ferrite is coarsened and the volume fraction of retained austenite is reduced. The hardness and ultimate tensile strength decrease sharply. The impact energy, yield strength, and elongation increase with elevated tempered temperature at 200–300 °C but decrease with elevated tempered temperature when the samples are tempered at 350 °C and 400 °C. The fracture appearance of all the samples after impact tests is a brittle fracture. The variation of the mechanical properties may be due to partial recovery and recrystallization. Full article

(This article belongs to the Special Issue Additive Manufacturing (AM) of Metallic Alloys)

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18 pages, 4688 KiB

Open AccessArticle

Finite Element Simulation of Multilayer Electron Beam Melting for the Improvement of Build Quality

by Manuela Galati, Oscar Di Mauro and Luca Iuliano

Crystals 2020, 10(6), 532; https://doi.org/10.3390/cryst10060532 - 23 Jun 2020

Cited by 10 | Viewed by 3543

Abstract

Macroscale modeling plays an essential role in simulating additive manufacturing (AM) processes. However, models at such scales often pay computational time in output accuracy. Therefore, they cannot forecast local quality issues like lack of fusion or surface roughness. For these reasons, this kind [...] Read more.

Macroscale modeling plays an essential role in simulating additive manufacturing (AM) processes. However, models at such scales often pay computational time in output accuracy. Therefore, they cannot forecast local quality issues like lack of fusion or surface roughness. For these reasons, this kind of model is never used for process optimization, as it is supposed to work with optimized parameters. In this work, a more accurate but still simple three-dimensional (3D) model is developed to estimate potential faulty process conditions that may cause quality issues or even process failure during the electron beam melting (EBM) process. The model is multilayer, and modeling strategies are developed to have fast and accurate responses. A material state variable allows for the molten material to be represented. That information is used to analyze process quality issues in terms of a lack of fusion and lateral surface roughness. A quiet element approach is implemented to limit the number of elements during the calculation, as well as to simulate the material addition layer by layer. The new material is activated according to a predefined temperature that considers the heat-affected zone. Heat transfer analysis accuracy is comparatively demonstrated with a more accurate literature model. Then, a multilayer simulation validates the model capability in predicting the roughness of a manufactured Ti6Al4V sample. The model capability in predicting a lack of fusion is verified under a critical process condition. Full article

(This article belongs to the Special Issue Additive Manufacturing (AM) of Metallic Alloys)

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11 pages, 23851 KiB

Open AccessArticle

The Fracture Behavior and Mechanical Properties of a Support Structure for Additive Manufacturing of Ti-6Al-4V

by Sebastian Weber, Joaquin Montero, Christoph Petroll, Tom Schäfer, Matthias Bleckmann and Kristin Paetzold

Crystals 2020, 10(5), 343; https://doi.org/10.3390/cryst10050343 - 27 Apr 2020

Cited by 10 | Viewed by 4058

Abstract

In the laser powder bed fusion processes for metal additive manufacturing, a support structure is needed to fix the part to the base plate and to support overhanging regions. Currently the importance of support structure for a successful build process is often underestimated [...] Read more.

In the laser powder bed fusion processes for metal additive manufacturing, a support structure is needed to fix the part to the base plate and to support overhanging regions. Currently the importance of support structure for a successful build process is often underestimated and some effects are not yet well understood. Therefore, this study investigates the fracture behavior and mechanical properties of thin additive manufactured struts using the titanium alloy Ti-6Al-4V and specific machine parameters for support structures. Tensile tests were performed for different strut diameters and the fracture surfaces were analyzed using a laser microscope and a scanning electron microscope. Additionally, the porosity was examined with micro-CT scans. The results were compared with a different set of parameters used for solid parts. The experiments revealed that struts produced with support parameters had no significantly lower tensile strength than the comparative parts. Despite that, some porosity and around two percent of defects on the fracture surface for parts using the solid parameter set have been found. Parts with support parameters show no porosity, even though the energy density is around 30% lower compared to the solid parameter set. Full article

(This article belongs to the Special Issue Additive Manufacturing (AM) of Metallic Alloys)

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14 pages, 2763 KiB

Open AccessArticle

Analytical Modeling of Residual Stress in Laser Powder Bed Fusion Considering Part’s Boundary Condition

by Elham Mirkoohi, Hong-Chuong Tran, Yu-Lung Lo, You-Cheng Chang, Hung-Yu Lin and Steven Y. Liang

Crystals 2020, 10(4), 337; https://doi.org/10.3390/cryst10040337 - 24 Apr 2020

Cited by 22 | Viewed by 3446

Abstract

Rapid and accurate prediction of residual stress in metal additive manufacturing processes is of great importance to guarantee the quality of the fabricated part to be used in a mission-critical application in the aerospace, automotive, and medical industries. Experimentations and numerical modeling of [...] Read more.

Rapid and accurate prediction of residual stress in metal additive manufacturing processes is of great importance to guarantee the quality of the fabricated part to be used in a mission-critical application in the aerospace, automotive, and medical industries. Experimentations and numerical modeling of residual stress however are valuable but expensive and time-consuming. Thus, a fully coupled thermomechanical analytical model is proposed to predict residual stress of the additively manufactured parts rapidly and accurately. A moving point heat source approach is used to predict the temperature field by considering the effects of scan strategies, heat loss at part’s boundaries, and energy needed for solid-state phase transformation. Due to the high-temperature gradient in this process, the part experiences a high amount of thermal stress which may exceed the yield strength of the material. The thermal stress is obtained using Green’s function of stresses due to the point body load. The Johnson–Cook flow stress model is used to predict the yield surface of the part under repeated heating and cooling. As a result of the cyclic heating and cooling and the fact that the material is yielded, the residual stress build-up is precited using incremental plasticity and kinematic hardening behavior of the metal according to the property of volume invariance in plastic deformation in coupling with the equilibrium and compatibility conditions. Experimental measurement of residual stress was conducted using X-ray diffraction on the fabricated IN718 built via laser powder bed fusion to validate the proposed model. Full article

(This article belongs to the Special Issue Additive Manufacturing (AM) of Metallic Alloys)

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16 pages, 14661 KiB

Open AccessArticle

A Low-Cost Electrochemical Metal 3D Printer Based on a Microfluidic System for Printing Mesoscale Objects

by Pengpeng Liu, Yawen Guo, Yihong Wu, Junyan Chen and Yabin Yang

Crystals 2020, 10(4), 257; https://doi.org/10.3390/cryst10040257 - 28 Mar 2020

Cited by 15 | Viewed by 6464

Abstract

For the additive manufacturing (AM) of metal objects, the powder-based fusion (PBF) method is routinely utilized to fabricate macroscale parts. On the other hand, electrochemical additive manufacturing (ECAM), in which metallic structures are deposited through the electrochemical reduction of metal ions, is a [...] Read more.

For the additive manufacturing (AM) of metal objects, the powder-based fusion (PBF) method is routinely utilized to fabricate macroscale parts. On the other hand, electrochemical additive manufacturing (ECAM), in which metallic structures are deposited through the electrochemical reduction of metal ions, is a promising technique for producing micro- and nanoscale objects. However, a gap exists in terms of fabricating mesoscale objects within the current AM techniques. The PBF method is limited by fabrication precision due to pronounced residual stresses, and most current ECAM systems are difficult to scale up to print mesoscale objects. In the present paper, the novel design of a low-cost ECAM 3D printer based on a microfluidic system is proposed for fabricating mesoscale metal parts. The meniscus-guided electrodeposition approach is utilized, in which a meniscus is formed between the print head and substrate, and electrodeposition is confined within the meniscus. A 3D object is fabricated by the meniscus moving with the print head according to the programmed pattern and the material subsequently being deposited at the designated locations. The key to the proposed design is to maintain a mesoscale meniscus, which normally cannot be sustained by the electrolyte surface tension with a print nozzle having a mesoscale diameter. Therefore, a microfluidic system, called the fountain pen feed system, constituting a semi-open main channel and comb structure, was designed to maintain a mesoscale meniscus throughout the printing process. Two materials, copper and nickel, with various geometric shapes were attempted to print by the proposed ECAM system, and, during the printing process, both fluid leaking and meniscus breaking were completely prevented. Free standing tilted copper pillars with controlled angles were printed to show the ability of the proposed design in fabricating 3D structures. A copper circuit was also printed on a non-conductive substrate to demonstrate a possible application of the proposed ECAM system in the fabrication of functional electronics. Full article

(This article belongs to the Special Issue Additive Manufacturing (AM) of Metallic Alloys)

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20 pages, 54812 KiB

Open AccessArticle

Experimental Study of Thermomechanical Processes: Laser Welding and Melting of a Powder Bed

by Yassine Saadlaoui, Julien Sijobert, Maria Doubenskaia, Philippe Bertrand, Eric Feulvarch and Jean-Michel Bergheau

Crystals 2020, 10(4), 246; https://doi.org/10.3390/cryst10040246 - 26 Mar 2020

Cited by 7 | Viewed by 2952

Abstract

In this study, an experimental approach was developed to analyze and better understand the laser welding and melting of a powder bed process. Different optical diagnostics tools (high-speed camera, infrared camera, pyrometer, etc.) were applied to measure different physical quantities (molten pool morphology, [...] Read more.

In this study, an experimental approach was developed to analyze and better understand the laser welding and melting of a powder bed process. Different optical diagnostics tools (high-speed camera, infrared camera, pyrometer, etc.) were applied to measure different physical quantities (molten pool morphology, temperature field, residual stresses, and distortions). As a result, measurements during the laser welding process facilitated the building of a database of experimental results (experimental benchmarks). The study of the melting of a powder bed enabled a better understanding of the physics related to the formation and behavior of the molten pool. These results can be used by researchers to improve and validate numerical simulations of these processes. Full article

(This article belongs to the Special Issue Additive Manufacturing (AM) of Metallic Alloys)

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22 pages, 8192 KiB

Open AccessArticle

Additive Manufacturing Redesigning of Metallic Parts for High Precision Machines

by Manuela Galati, Flaviana Calignano, Marco Viccica and Luca Iuliano

Crystals 2020, 10(3), 161; https://doi.org/10.3390/cryst10030161 - 01 Mar 2020

Cited by 13 | Viewed by 3013

Abstract

The conventional approach to design and manufacturing often has geometries with an efficient material distribution. For the high-precision machines, that approach involves the design of heavy components that guarantees the stiffness requirements. However, the higher the weight of the part, the higher inertia [...] Read more.

The conventional approach to design and manufacturing often has geometries with an efficient material distribution. For the high-precision machines, that approach involves the design of heavy components that guarantees the stiffness requirements. However, the higher the weight of the part, the higher inertia it has. As a result, when the feed axes are accelerated, the inertial forces deform the machine components and the precision of the machine is reduced. This study investigated the designing for additive manufacturing (DfAM) and designing for assembly (DfA) to increase the material efficiency of components for high-precision applications. A new methodology which considered the design and manufacturing issues and machining as well is given. A comprehensive model for cost evaluation of the part is presented. The case study refers to the rails and the bracket that support and move the flying probe of a testing machine for micro-electromechanical systems (MEMS). The weight of the rails has been decreased by 32% and the components to be assembled have been reduced from 16 to 7. The optimized bracket is more than 50% stiffer than the original one, 10% lighter, and economically competitive. Full article

(This article belongs to the Special Issue Additive Manufacturing (AM) of Metallic Alloys)

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Review

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26 pages, 4790 KiB

Open AccessReview

In Situ Monitoring Systems of The SLM Process: On the Need to Develop Machine Learning Models for Data Processing

by Pinku Yadav, Olivier Rigo, Corinne Arvieu, Emilie Le Guen and Eric Lacoste

Crystals 2020, 10(6), 524; https://doi.org/10.3390/cryst10060524 - 18 Jun 2020

Cited by 51 | Viewed by 6983

Abstract

In recent years, technological advancements have led to the industrialization of the laser powder bed fusion process. Despite all of the advancements, quality assurance, reliability, and lack of repeatability of the laser powder bed fusion process still hinder risk-averse industries from adopting it [...] Read more.

In recent years, technological advancements have led to the industrialization of the laser powder bed fusion process. Despite all of the advancements, quality assurance, reliability, and lack of repeatability of the laser powder bed fusion process still hinder risk-averse industries from adopting it wholeheartedly. The process-induced defects or drifts can have a detrimental effect on the quality of the final part, which could lead to catastrophic failure of the finished part. It led to the development of in situ monitoring systems to effectively monitor the process signatures during printing. Nevertheless, post-processing of the in situ data and defect detection in an automated fashion are major challenges. Nowadays, many studies have been focused on incorporating machine learning approaches to solve this problem and develop a feedback control loop system to monitor the process in real-time. In our study, we review the types of process defects that can be monitored via process signatures captured by in situ sensing devices and recent advancements in the field of data analytics for easy and automated defect detection. We also discuss the working principles of the most common in situ sensing sensors to have a better understanding of the process. Commercially available in situ monitoring devices on laser powder bed fusion systems are also reviewed. This review is inspired by the work of Grasso and Colosimo, which presented an overall review of powder bed fusion technology. Full article

(This article belongs to the Special Issue Additive Manufacturing (AM) of Metallic Alloys)

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