Production Of Metal Components Research Articles

Microstructural and Mechanical Characterization of Square‐Celled TRIP Steel Honeycomb Structures Produced by Electron Beam Melting

The powder‐bed additive manufacturing (AM) technology electron beam melting (EBM) is suitable for the production of metallic components with complex geometries. Therefore, it is an appropriate method of generating lightweight structures to save material and energy, which is of high importance for the transport industry. The microstructure of additive manufactured materials is usually characterized by columnar grains shape, oriented along the building direction. Therefore, the mechanical properties are strongly affected by anisotropy. Herein, the synthesis and the microstructure of CrMnNi transformation‐induced plasticity (TRIP) steel by EBM is examined. This steel is well suited for AM due to the formation of fine‐grained microstructure instead of columnar one through multiple‐phase transformations. Square‐celled honeycomb structures are produced and improved to generate damage‐tolerant struts. The removal of slightly sintered powder from the cavities of square‐celled structures is quantified. Out‐of‐plane compression tests at quasistatic loading rates show that the strength of honeycomb structures rises with increasing energy input during EBM due to lower material porosity. Therefore, an enhanced mechanical energy absorption capacity is achieved which is favorable for the production of cellular structures.

The Use of the Gas Nitriding Process for the Nitridation of Powder for Laser Powder Bed Fusion

AbstractAdditive manufacturing in the powder bed by means of laser powder bed fusion (L-PBF) combines the fast production of metallic components with complex geometrical structures with a high degree of customization and low raw material consumption. However, there is a high demand for the development of new alloys to achieve the desired properties of additively manufactured parts. Due to a lack of knowledge, only a small group of steel powders are currently available for L-PBF. As an example, Cr and CrMn steel powders with additional alloyed nitrogen could be used for L-PBF products for Ni-free medical devices. The present work investigates the possibility of alloying nitrogen to austenitic steel alloy powder and high alloyed martensitic steel powder via gas nitriding. For this purpose, an X30CrMo7-2 powder and an AISI 316L powder for additive manufacturing were arranged to form powder beds of different heights and nitrided at different temperatures, times and nitriding potentials. The nitrogen content was determined from the samples taken at different heights of the powder beds. Individual powder particles were examined by means of metallography, scanning electron microscopy and electron probe micro analysis. It is shown that the nitrogen concentration in the powder is essentially determined by the nitriding temperature. In the X30CrMo7-2 powder, nitride precipitation also occurs at high temperature and N and C gradients are present in the particles with an average nitrogen content of up to 4 mass%. In the 316L powder, a homogeneously distributed nitrogen content of 0.35 mass% can be achieved after gas nitriding at 420 °C for 24 h. The flow properties of both powders are hardly affected by gas nitriding.

Development of Metal Powder Hot Embossing: A New Method for Micromanufacturing

Hot embossing is a small-scale, low-cost processing technology that can deliver products to the market in a short time. This microreplication technology is well established to produce polymeric components and has applications in several industrial sectors. The use of micropowder hot embossing in the production of metal components is an emerging and challenging process that, when compared to other typical technologies, brings some economic advantages in a volatile market with an increasing tendency to manufacture customized products. The main objective of this review is to analyze the potential of powder hot embossing and its developments in the production of metallic microparts/components. This technology requires four distinct steps: (1) production feedstock (preparation of mixtures), (2) hot embossing (shape forming), (3) debinding and (4) sintering. These steps are interrelated and influence the characteristics of the final metallic microparts. This study summarizes the approaches implemented for the use of different metallic powders and polymeric binder systems for the preparation of the feedstock, the mold materials and the critical conditions tested in the embossing step to produce green parts, and the production of the final parts through the application of debinding and sintering. Powder hot embossing is a viable replication technology that allows the production of new metallic microcomponents, contributing to the global scientific effort of miniaturizing manufacturing process, equipment and products. The merit of powder hot embossing for industrialization needs further development to assert itself in the market and compete with other micromanufacturing techniques.

Solid-state additive manufacturing high performance aluminum alloy 6061 enabled by an in-situ micro-forging assisted cold spray

Cold spraying is a competitive additive manufacturing method featuring several unique characteristics and allows large-scale production of metallic components from a wide range of materials. In literature, high performance cold sprayed aluminum deposits produced using high-cost helium gas have been qualified for various applications. In this study, high performance aluminum alloy 6061 (AA6061) deposits were produced through a cold spray method using low-cost nitrogen gas enabled by an in-situ micro-forging effect (MF-CS). Results show that the MF-CS AA6061 deposit presents very low porosity as well as high ultimate tensile strength (UTS) and elastic modulus (E). Moreover, the MF-CS AA6061 deposit consists of superior equiaxed submicron fine Al grains with random orientations. However, the severe work hardening induced by intensive particle plastic deformation during deposition leads to very low ductility of the MF-CS AA6061 deposit. To eliminate this limitation, three strategies of heat treatments (stress relieving, recrystallization annealing and T6) were performed to the MF-CS AA6061 deposit. It was found that heat treatment generated complex effects on both inter-particle bonding and inner-particle microstructure (grain size, dislocation density and precipitation) and different strategies lead to different mechanical properties of AA6061 deposits. Among them, T6 heat-treated AA6061 deposits give the best overall mechanical properties with comparable UTS and E and only slightly inferior ductility to the corresponding T6 bulk.

Guidelines to compare additive and subtractive manufacturing approaches under the energy demand perspective

In order to characterise the environmental performance of additive manufacturing (AM) processes, comparative analyses are required. Different manufacturing approaches (such as additive and subtractive ones), besides adopting different equipment, use different kinds and amounts of material. Therefore, the material-related flow has to be followed throughout the entire product life. Differences in environmental impact arise at each step of the life cycle: material production, manufacturing, use, disposal, and transportation. A life cycle-based methodology able to take due account of all the factors of influence on the total energy demand for the production of metal components is given in this paper. Decision support tools for identifying the most sustainable manufacturing route (subtractive versus AM-based approaches) are presented for different scenarios. The aim of the present paper is to contribute to the debate concerning the environmental impact characterisation of AM processes.

Microstructure by design: An approach of grain refinement and isotropy improvement in multi-layer wire-based laser metal deposition

The additive production of metallic components with high-throughput is usually associated with high process temperatures and slow cooling rates. This typically results in strongly oriented columnar grain growth along the building direction of the structure having exceedingly large grain sizes. As a result, such structures show typically low strength and anisotropic mechanical behaviour in as-deposited condition. Consequently, post-processing is commonly performed to homogenize and eventually increase the mechanical properties of the deposited structures. In this regard, precise control of the applied process energy allows a modification of the local temperature distribution and cooling conditions during the additive manufacturing process, which strongly influence the resulting solidification microstructure. The aim of the present study is the development of an approach that allows to influence the solidification conditions in wire-based laser metal deposition of an Al-Mg alloy through specific adjustments of the laser irradiation. It was found that significantly different solidification microstructures in as-deposited condition can be achieved by adjusting the laser beam irradiance within a range resulting in conduction mode welding conditions while keeping the heat input constant. The application of high laser beam irradiances, close to the transition to keyhole mode welding, results in structures with a homogeneous large-grained solidification microstructure exhibiting a degree of anisotropy of around 12% between building direction and the direction of deposition. In contrast, the use of low laser beam irradiance close to the lower limit of stable melting, results in structures with a significantly refined microstructure. Consequently, an increase of yield strength of up to around 20% and microhardness of up to 13%, as compared to structures processed with high laser beam irradiance, could be obtained. Moreover, the anisotropy of the as-deposited structure was reduced to a degree lower than 2%.

In-process closed-loop control for stabilising the melt pool temperature in selective laser melting

Additive manufacturing processes are gaining more importance in the industrial production of metal components, as they enable complex geometries to be produced with less effort. The process parameters used to manufacture a wide variety of components are currently kept constant and closed-loop controls are missing. However, due to the part geometry that causes varying heat flow to neighbouring powder and solidified sections or due to deviations in the atmosphere caused by fumes within the work area, there are changes in the melt pool temperature. These deviations are not considered by system control, so far. It is, therefore, advisable to measure the melt temperature with sensors and to regulate the process. This work presents an approach that enables fast process control of the melt pool temperature and combines a closed-loop control strategy with a feedforward approach. The control strategies are tested by proof-of-concept experiments on a bridge geometry and partly powder-filled steel plates. Furthermore, results of a finite element simulation are used to validate the experimental results. Combining closed-loop and feedforward control reduces the temperature deviation by up to 90%. This helps to prevent construction errors and increases the part quality.

Fatigue properties of SLM-produced Ti6Al4V with various post-processing processes

Titanium and its alloys are very popular for various applications. They are the most widely used materials for biomedical applications. Titanium-based materials have shown excellent biocompatibility, as well as mechanical properties and corrosion resistance. The high fatigue life of this material is often demanded, therefore fatigue testing is necessary. Additive manufacturing (AM) is an innovative, widely investigated method for the production of metal components. AM allows the possibility of producing complex shaped components with near to net shape. Selective laser melting (SLM) is one of the most promising AM techniques. This research explores the fatigue behaviour of titanium alloy Ti6Al4V, produced by SLM. Different conditions and surface preparations for additive manufactured specimens were investigated by fatigue testing and then compared to each other. The aim of this research is to explore the influence of surface machining and processing by hot isostatic pressing (HIP) on the fatigue properties of the SLM produced components.

Characterization of Inconel 625 fabricated using powder-bed-based additive manufacturing technologies

The purpose of this study was to perform a comparative analysis of powder-bed-based additive manufacturing (AM) technologies during the production of metallic components using Inconel 625 powder material. The AM technologies explored in this study include electron beam powder bed fusion (EPBF), laser powder bed fusion (LPBF), and binder jetting technology. Samples were fabricated in two build directions (X and Z build orientations) for this evaluation process, where all specimens underwent a hot isostatic pressing (HIP) post-process. The comparison was made in terms of microstructure and mechanical properties including ultimate tensile strength (UTS), yield strength (YS), percent elongation, and modulus of elasticity (E). Microstructural characterization showed evidence of equiaxed grain formation for binder jetting and LPBF parts, whereas EPBF parts displayed a more columnar grain formation parallel to the build direction. Six specimens were tested per technology, three built in the X orientation and three built in the Z orientation. All six specimens were built in a single run of each AM machine. Results indicated that all three technologies are capable of meeting the minimum requirements of the ASTM F3056-14 standard for parts produced in the X orientation, with properties that are similar to wrought Inconel 625. In the Z orientation, however, only LPBF was able to meet the minimum standard requirements. Through the comparative analysis of the mechanical properties, this work showed that LPBF outperformed the other technologies in a majority of the evaluated properties, followed by EPBF and binder jetting. An analysis of the fracture surfaces of tensile specimens was also performed, and it indicated ductile fracture (dimple rupture) for the specimens produced with all three of the AM technologies studied. Nevertheless, the characterization also showed certain differences in the fractured surfaces, such as the presence of un-sintered powder particles for the binder jetting processed Inconel 625, or the development of the so called woody structure for the EPBF processed material. This study can be used to determine distinct characteristics between the three powder-bed-based technologies for the fabrication of Inconel 625 that can further include other technologies and materials using similar approaches.

Structure and Properties of Carbon Steel Wire in Drawing

A method of continuous deformational nanostructuring of wire is described. In the method, a continuously moving wire is subjected simultaneously to tensile deformation in drawing, flexural deformation on passing through a roller system, and torsional deformation. This combination permits wide variation in its mechanical properties, ensuring both high strength and plasticity. The benefits of such deformation are the use of a tool already employed in the production of metal components; compatibility with the speeds of coarse and moderate wire drawing; and simplicity of the equipment. Laboratory apparatus for this method is described. Carbon steel 50 wire is selected for investigation, since it in great demand. The chemical composition and mechanical properties of the wire in the initial state are described. Experiments are conducted to investigate the effectiveness of the proposed differential nanostructuring in producing ultrafine-grain structure in the wire. The deformation conditions of the wire are described, as well as the drawing process. The transverse and longitudinal microstructure of the carbon steel 50 wire at the surface and in the center after different types of deformational treatment is investigated. In the experiments, the influence of the type of deformational treatment on the microstructure of the steel and its anisotropy over the wire cross section is established. The compliance of the wire’s mechanical properties with current standards is verified. After all types of treatment, its mechanical properties are consistent with State Standard GOST 17305–91. Metallographic data and mechanical test results after combined deformational treatment indicate that such combinations of deformation provide a promising approach to creating ultrafine-grain structure in carbon wire.

The Value of Metal Additve Manufacturing with Diode Lasers

AbstractLaser powder bed fusion (LPBF) is an established additive manufacturing (AM) process for the production of metal components. Despite its great potential, the technology has not yet arrived in many small and medium enterprises. The article shows the potential of metal 3D printing with diode lasers to increase the customer value of market accessibility.

Powder recycling in laser beam melting: strategies, consumption modeling and influence on resource efficiency

Laser beam melting (LBM) is a powder-bed and laser-based additive manufacturing technology that is increasingly used for the production of metal components. For a sustainability assessment of a production technology, the global warming potential (GWP) can be used, which is commonly referred to as CO2-footprint. Looking at the resource demand of LBM, material losses and powder recycling play a significant role. In the LBM build-up process, powder material is selectively solidified, generating the part layer-by-layer. The non-solidified powder material can be recycled, which is beneficial to the resource efficiency of the process. Due to considerations regarding powder quality degradation, the number of reuse powder cycles in industrial practice varies significantly, ranging from only one to more than several dozen cycles. Similarly, material losses during the process have shown to differ between LBM machines. However, previous approaches for LBM resource efficiency assessment lack a detailed representation of these two factors. In this study, two interacting models are introduced for the evaluation of the GWP of LBM parts. Firstly, a powder reuse cycle calculation model is described. Secondly, a LBM resource and energy consumption model based on the CO2PE!-methodology is put forward with a refined focus on powder recycling and material losses. The models are implemented and validated based on three LBM production use cases including the acquisition of resource and energy consumption data for three commercial LBM machines. GWP-impact values are used from the ProBas database, provided by the German Federal Environmental Agency. Based on the results regarding the three LBM use cases, the role of powder recycling and material losses on the GWP-impact of LBM during the production phase is discussed. The results show that the number of attainable powder reuse cycles lies around 35 cycles (ranging from 1 to 117 cycles) for the analyzed LBM production scenarios when applying the suggested powder recycling strategy. If powder is not recycled and only used once, more than 90% of the powder batch might be discarded. The volume-specific CO2-equivalent of 0.175 kgCO2eq/cm3 can be used as a rule of thumb for a quick estimation of the GWP for LBM parts made from Al-alloy or steel. Electric energy consumption constitutes for the largest share of GWP-impact, followed by the solidified metal powder and the occurring powder losses.

Automated Manufacturing of Mechatronic Parts by Laser-Based Powder Bed Fusion

The powder-bed-based laser beam melting process (L-PBF) has become one of the most reliable and popular additive manufacturing technologies in the field of industrial production of metal components. Moreover, it is constantly evolving to ensure lower costs due to higher productivity as well as to enable the processing of new materials, such as tungsten or copper-alloys. In terms of machine developments, a number of trends are observable. On the one hand, machines become able to produce multi-material parts with an arbitrary distribution of at least two different materials. Therefore, the existing powder delivery system must be adapted. As multiple approaches for doing so already exist, it must be decided which is the most suitable. On the other hand, a further goal is to integrate sensors or actuators automatically, to create structural parts with fully encapsulated electronic components. For this automated process, a pick-and-place concept must be developed and integrated into an existing L-PBF machine. To implement this automated process extension, several adjustments to the system must be implemented. This paper presents approaches for realising the described concepts and the first results of the adapted manufacturing processes.

Towards criteria for sustainable process selection: On the modelling of pure subtractive versus additive/subtractive integrated manufacturing approaches

Additive Manufacturing (AM) processes can be counted among the disruptive technologies that are capable of transforming conventional manufacturing routes. The ability to create complex geometries, the reduction in material scraps during manufacturing, and the light-weighting due to the think-additive redesign of the components represent the main points of strength of AM. However, for some applications (such as the production of metal components for the automotive and aerospace industries), the surface finishing and dimensional/geometrical part tolerancing that can be achieved via AM processes might not be adequate to satisfy the imposed product specifications, and finish machining operations are often required. A machining approach and an integrated production route, based on an additive manufacturing process plus finish machining, have been compared in this paper. The primary energy demand and the CO2 emissions have been modelled for all the life cycle stages within a sustainable development context. The main result of the research work is a criterion for the selection of the most environmentally friendly manufacturing approach, while varying the productive scenario (i.e., the masses of the process scraps, the machined chips, and the support structures). The application of such a tool to the production of metal components made of either Ti-6Al-4V or stainless steel is discussed.

Fatigue characterization of Titanium Ti-6Al-4V samples produced by Additive Manufacturing

Additive Manufacturing offers real opportunities in Thales, since it enables a flexible and cost-effective production of metallic components directly from a 3D digital data model. The manufacture of the parts, layer by layer, allows building more complex geometries by adding new functionalities or reducing the weight. The products of Thales can be more competitive and attractive.Studying and analysing the mechanical properties of such samples is essential. In order to be able to choose the eligible parts, design these parts and ensure their robustness, it is necessary to understand the static and fatigue behaviour of materials built by Additive Manufacturing and, more particularly, the damaging process regarding the microstructure.Following a first study on the static properties of a Titanium alloy used within Thales, a large set of fatigue tests, including both HCF and LCF, have been performed to evaluate the fatigue performances of Ti-6Al-4V samples built by a powder bed fusion process. The fatigue mechanisms and the obtained lifetimes were compared with more conventional processes (casting, wrought).In this paper, the results of these fatigue tests on Titanium (Ti-6Al-4V) samples will be presented. Different parameters have been compared: building orientation, heat treatment (HIP) and post-machining. The fracture mechanisms have also been analysed by performing a correlation between the microstructure analysis (porosity, metallography) and fractographies. It is shown that fatigue performances depend on the selected parameters but these effects are different, depending on the loading domain (HCF, LCF).

Trend and Development of Semisolid Metal Joining Processing

The semisolid metal joining (SSMJ) process or thixojoining process has recently been developed based on the principles of SSM processing, which is a technology that involves the formation of metal alloys between solidus and liquidus temperatures. Thixojoining has many potential benefits, which has encouraged researchers to carry out feasibility studies on various materials that could be utilized in this process and which could transform the production of metal components. This paper reviews the findings in the literature to date in this evolving field, specifically, the experimental details, technology considerations for industrialization, and advantages and disadvantages of the various types of SSMJ methods that have been proposed. It also presents details of the range of materials that have been joined by using the SSMJ process. Furthermore, it highlights the huge potential of this process and future directions for further research.

A new approach to the design and optimisation of support structures in additive manufacturing

Support structures are required in several additive manufacturing (AM) processes to sustain overhanging parts, in particular for the production of metal components. Supports are typically hollow or cellular structures to be removed after metallic AM, thus they represent a considerable waste in terms of material, energy and time employed for their construction and removal. This study presents a new approach to the design of support structures that optimise the part built orientation and the support cellular structure. This approach applies a new optimisation algorithm to use pure mathematical 3D implicit functions for the design and generation of the cellular support structures including graded supports. The implicit function approach for support structure design has been proved to be very versatile, as it allows geometries to be simply designed by pure mathematical expressions. This way, different cellular structures can be easily defined and optimised, in particular to have graded structures providing more robust support where the object’s weight concentrate, and less support elsewhere. Evaluation of support optimisation for a complex shape geometry revealed that the new approach presented can achieve significant materials savings, thus increasing the sustainability and efficiency of metallic AM.

Thermal Analysis during Solidification of Mg-4%.wtAl Alloy during Lost Foam Casting Process

The lost foam casting (LFC) process utilizes the expanded polystyrene (EPS) foam pattern for the production of metallic components. The thermal degradation of the foam pattern has a significant effect on microstructure of the component. Dendrite coherency is important for the determination of the formation of the solidification structure and cast ability of alloys. The effects of the dendrite coherency on grain size in Mg-4Al alloy have been studied using the two-thermocouple thermal analysis technique in the solidified sample. The results also indicate that the grain size increases with the temperature interval between liquids (TN) and dendrite coherency point (TDCP), The solid fraction at DCP (fsDCP) expressed in percent strongly dependents on the dendrite morphology during solidification.

Automated Aircraft Sheet Metal Component Production Technologies

This article comprehensively presents an overview of the technological advances in automated aircraft sheet metal component production technology developments due to the initiative by the Aeronautical Development Agency, Ministry of Defense, Government of India, since 1989 in collaboration with the Indian Institute of Technology, Bombay. Commencing with a modest computer-aided flat pattern development software system suitable for a class of sheet metal components, this activity after several stages of development has now resulted in the development of full-fledged, personal-computer-based graphical interactive, three-dimensional application flat pattern development and automated production loft generation system. This research, encompassing the practical methods (exclusively developed for flat pattern software), literature survey, development of key algorithms suitable for designing a system for automated loft generation for a variety of surfaces with complex geometric features characteristic of aircraft sheet metal components with the aid of a wide choice of surface model creations, and testing and validation (carried out through an associated aircraft factory, Hindustan Aeronautics Limited), is now being published through four full-length papers concluding with the present paper. In fact, comprehensive illustrations of production lofts sampled from over thousands of parts used in the factory pertinent to the Indian Light Combat Aircraft (termed as Tejas) and other projects like Advanced Light Helicopter (termed as Dhruv) sheet metal components are included here to provide insight into these developments, and also to provide a glimpse of the success of the mission of indigenous automated aircraft sheet metal component manufacture.

On the advantages of using powder metallurgy in new light metal alloy design

Historically, the production of metallic components for the automotive and aerospace industries has been dominated by wrought and ingot metallurgy metal forming practices. These technologies offer considerable design flexibility to engineers and are readily amenable to ferrous and nonferrous alloys alike. However, in applications that require precise dimensional control, the tolerances attainable are generally inadequate. This represents a formidable limitation and mandates the incorporation of expensive secondary machining. Furthermore, because these processes are carried out under conditions that approach those of equilibrium, these technologies are also faced with rather strict limitations on the range of alloy chemistries that can be employed. As the demands for improved material performance and process economics increase, the aforementioned shortcomings become increasingly important. Consequently, considerable attention has and continues to be focused on alternate metal forming techniques such as powder metallurgy (P/M). Using the P/M approach, dimensional tolerances are commonly improved by one to two orders of magnitude and alloy chemistry limitations are essentially eliminated. The work described herein provides an overview of select P/M techniques developed by the authors, initially to enhance the hardness and tensile properties of aluminum-based P/M alloys through a mineral dissociation/diffusion process. This is expanded through alloy development research wherein a P/M processing route designed to simulate industrial practices is used in the most recent work based on the effects of rare earth additions on selected mechanical properties of aluminum P/M alloys. These results include a compilation of theoretical calculations (thermodynamics and diffusion rates) that are supported by experimental data using techniques that include electron microprobe analyses, X-ray diffraction, tensile testing, and wear testing. Specific findings are that minerals/compounds such as wollastonite and silver nitrate can be successfully reacted to enhance selected mechanical properties of aluminum P/M alloys and that wear resistance may be improved through a P/M approach applied to AA2014.