Additive Manufacturing Of Metal Parts Research Articles

Plasma electrolytic polishing of additively manufactured metal parts: Optimizing the post processing workflow

Additive manufacturing of metal parts is gaining acceptance in industry due to its unique manufacturing capabilities. Higher surface roughness of printed parts is one of the major challenges of this advanced manufacturing technique, which requires a crucial post-processing stage before the components can be used in practice. This study investigates the influence of plasma electrolytic polishing (PeP) and the combination of PeP and particle blasting as a post processing technique for additively manufactured stainless steel samples. The results show a 70% improvement in surface roughness after 10 minutes of particle blasting and 3 minutes of PeP in sequence and presents the possibility of optimizing processing time to achieve better surface qualities with minimal post processing time.

Comparison between Micro-Powder Injection Molding and Material Extrusion Additive Manufacturing of Metal Powders for the Fabrication of Sintered Components

Original compositions based on iron micro-powders and an organic binder mixture were developed for the fabrication of sintered metallic elements with micro-powder injection molding (µPIM) and material extrusion additive manufacturing of metal powders (MEX). The binder formulation was thoroughly adjusted to exhibit rheological and thermal properties suitable for µPIM and MEX. The focus was set on adapting the proper binder composition to meet the requirements for injection/extrusion and, at the same time, to have comparable thermogravimetric characteristics for the thermal debinding and sintering process. A basic analysis of the forming process indicates that the pressure has a low influence on clogging, while the temperature of the material and mold/nozzle impacts the viscosity of the composition significantly. The influence of the Fe micro-powder content in the range of 45–60 vol.% was evaluated against the injection/extrusion process parameters and properties of sintered elements. Different debinding and sintering processes (chemical and thermal) were evaluated for the optimal properties of the final samples. The obtained sintered elements were of high quality and showed minor signs of binder-related flaws, with shrinkage in the range of 10–15% for both the injection-molded and 3D printed parts. These results suggest that, with minor modifications, compositions tailored for the PIM technique can be adapted for the additive manufacturing of metal parts, achieving comparable characteristics of the parts obtained for both forming methods.

Latest developments in coaxial multiwire high-power laser cladding

Laser cladding is widely used in the industry to precisely apply tailored surface coatings, as well as three-dimensional deposits for repair and additive manufacturing of metallic parts. However, the processing of larger components is economically challenging mainly because of low deposition rates. At Fraunhofer IWS, a Laserline fiber-coupled diode laser with 20 kW power has been employed for over a decade to develop competitive coating solutions with powder-based laser cladding. The deposition rates achieved with this technology is comparable to common PTA technique at the same time bringing significant advantages in terms of reduced heat affected zone, distortion, and savings in material resources. While high-power powder-based laser cladding is an industrially established coating technology, for example, to coat hydraulic cylinders or most recently brake discs, a high-productivity solution for wire-based processes is still challenging. Fraunhofer IWS has developed a new nozzle for high-power high-productivity laser wire cladding for coating and additive manufacturing, the so-called COAXquattro. This system enables to feed at the same time four wires into the melt pool, reaching deposition efficiencies in the same range as a powder-based laser process. For selected materials, the improvement in coating quality compared to powder laser cladding is achieved. Furthermore, with COAXquattro system simultaneous feeding of powder particles to wire cladding presents a great potential for in situ alloying and cost-effective production of new compositions on material alloying or hardmetal-reinforced composites for coating application and 3D additive manufacturing.

Advanced Materials and Manufacturing Techniques for Additive Manufacturing of Metal Parts

Advanced Materials and Manufacturing Techniques for Additive Manufacturing of Metal Parts

The Corrosion Behaviour of Additively Manufactured AlSi10Mg Parts Compared to Traditional Al Alloys

Additive manufacturing of metal parts in the motorsport industry is becoming a decisive technology for producing lightweight and rigid parts, with increasing applications as the costs decrease. Among the available metal alloys, AlSi10Mg is one of the most widely used. In this paper, the corrosion resistance of additively manufactured AlSi10Mg is compared with that of other traditionally manufactured aluminium alloys widespread in the automotive industry. Several potentially corrosive agents, typical of vehicle applications, were used: salty water, motor oil, suspension oil, cooling fluid and gasoline. Corrosion tests were conducted at both room temperature and 90 °C. The effects of heat and surface treatments were evaluated separately. The samples were visually inspected and weighed to evaluate the corrosion rate with the aid of SEM and EDS analysis. Additively manufactured AlSi10Mg generally showed better corrosion resistance in the stress-relieved condition as compared to the T6-treated state, with slightly better results for the polished samples. Motor oil, suspension oil, cooling fluid and gasoline did not significantly corrode the specimens, except for the T6-treated AlSi10Mg samples at 90 °C. However, the corrosion rate was always higher than traditionally manufactured aluminium alloys tested for comparison.

Direct additive manufacturing of metal parts for automotive applications

Additive manufacturing or three-dimensional (3D) printing offers tremendous opportunities for the automotive industry to reduce vehicle weight and improve vehicle performance through consolidating parts, tailoring material properties, enabling multifunctional components, and simplifying manufacturing processes. However, additive manufacturing research for direct manufacturing of automotive components is limited, partially because of the sheer volume of automotive production. In this paper, we explore the potential of direct manufacturing of metallic vehicle components using additive manufacturing coupled with the generative design approach. Using a radar mounting bracket as an example, we show that desired part strength and safety performance can be achieved with 42 % weight reduction and simplified manufacturing and assembly process. A production cost analysis was also conducted based on two mainstream additive manufacturing systems. The result suggests that the cost of metal powder is the limiting factor for wider adoption of additive manufacturing in the automotive industry.

3D characterization of the microstructure of LPBF- fabricated Inconel 718 alloy

Laser powder bed fusion method is popularly applied in the additive manufacturing of metal parts. The void defect and microstructure are the main factors which determine their mechanical properties. However, the characterization of microstructure and cavities is two dimensional, which is hard to show the spatial profile. In this paper, in order to explore the microstructure and defects in three dimensions, the combined continuously slicing and microstructure observation was used to investigate the microstructure of an Inconel 718 sample. The sample was sliced 468 layers with thickness of 1 µm by xenon ion beam, a 142.8 µm* 107 µm* 46.8 µm microstructure cube was reconstructed. From the 3D model, the melt pool, cavity, pore and grains and their orientations were analyzed. The results provide spatial features of its microstructure. The equi-axed grains are among the coarse column grains, and some are the original grains of insufficiently melt or totally unmelt powder particles. The results tell the difference of the two kinds of voids, i.e., cavity and pore. Keywords: laser powder bed fusion, Inconel 718, microstructure, 3D characterization, pore, cavity

3D characterization of the microstructure of LPBF fabricated Inconel 718 alloy

Laser powder bed fusion method is popularly applied in the additive manufacturing of metal parts. The void defect and microstructure are the main factors which determine their mechanical properties. However, the characterization of microstructure and cavities is two dimensional, which is hard to show the spatial profile. In this paper, in order to explore the microstructure and defects in three dimensions, the combined continuously slicing and microstructure observation was used to investigate the microstructure of an Inconel 718 sample. The sample was sliced 468 layers with thickness of 1 µm by xenon ion beam, a 142.8 µm* 107 µm* 46.8 µm microstructure cube was reconstructed. From the 3D model, the melt pool, cavity, pore and grains and their orientations were analyzed. The results provide spatial features of its microstructure. The equi-axed grains are among the coarse column grains, and some are the original grains of insufficiently melt or totally unmelt powder particles. The results tell the difference of the two kinds of voids, i.e., cavity and pore.

Fabrication sequence optimization for minimizing distortion in multi-axis additive manufacturing

Additive manufacturing of metal parts involves phase transformations and high temperature gradients which lead to uneven thermal expansion and contraction, and, consequently, distortion of the fabricated components. The distortion has a great influence on the structural performance and dimensional accuracy, e.g., for assembly. It is therefore of critical importance to model, predict and, ultimately, reduce distortion. In this paper, we present a computational framework for fabrication sequence optimization to minimize distortion in multi-axis additive manufacturing (e.g., robotic wire arc additive manufacturing), in which the fabrication sequence is not limited to planar layers only. We encode the fabrication sequence by a continuous pseudo-time field, and optimize it using gradient-based numerical optimization. To demonstrate this framework, we adopt a computationally tractable yet reasonably accurate model to mimic the material shrinkage in metal additive manufacturing and thus to predict the distortion of the fabricated components. Numerical studies show that optimized curved layers can reduce distortion by orders of magnitude as compared to their planar counterparts.

Fatigue properties of Scalmalloy® processed by laser powder bed fusion in as-built, chemically and conventionally machined surface condition

Additive manufacturing of metallic parts via laser powder bed fusion has is attractive for applications such as aerospace engineering due to the high weight-saving potential, which is based on the ability of the process to produce complex designs. The aluminum alloy Scalmalloy® can increase this potential for lightweight design further with its high strength and high ductility. These advantages already led to a variety of use cases for statically loaded parts. Research on the dynamic mechanical behavior of Scalmalloy® is far less extensive than for other aluminum materials such as AlSi10Mg. There is limited insight into the fatigue behavior and mechanisms of Scalmalloy® in as-built and various surface-finished states. This study aims to understand the fatigue-fracture mechanisms of Scalmalloy® not only in two different as-built surface conditions but also in machined and chemically milled surface states. Fatigue specimens with four different surface modifications were produced, their surface morphology was characterized and correlated to the fatigue performance. Fractographic analysis was conducted to reveal the fracture-inducing defects. Defect-based modeling is shown to describe the influence of defect size on the fatigue behavior and verifies that the fatigue properties are independent of sample size. Kitagawa-Takahashi-diagrams are drawn upon to explain the influence of defect size, and an equivalent initial flaw size (EIFS) was defined and coupled to an El-Haddad-type model to arrive at a unified model predicting the fatigue strength for all four surface conditions despite their differences in defect nature.

Effect of print parameters on additive manufacturing of metallic parts: performance and sustainability aspects

In this study, the effects of print parameters on the mechanical properties of additively manufactured metallic parts were investigated using a tensile test. The 17-4 PH stainless steel specimens with two print parameters, including infill density and pattern orientation, were fabricated by additive manufacturing (AM) using the bound metal deposition (BMD) technique. The mechanical properties considered in this study are the Young’s modulus and ultimate tensile strength. The results demonstrate that the pattern orientations do not affect the Young’s modulus of the infill specimen with the triangular pattern. In contrast, the ultimate strength significantly varies depending on the pattern orientations, where the samples with the pattern orientation of zero degrees yield the best ultimate strength. In fact, the mechanical properties of infill specimens increase with their infill density. However, when operating cost and time are considered, an index for estimating performance and sustainability is consequently established. The relationship between the normalized ultimate strength of an infill specimen and the relative density is defined as the weight efficiency. The index for assessing a sustainable product is characterized by the weight efficiency versus sustainable parameter(s). The index can help end users select an appropriate infill density for AM products by considering the operating cost and time. Different cost models, including material-only costs, direct costs, and total costs, can be included in the index model to assess a sustainable product in a particular cost context.

Review of quality issues and mitigation strategies for metal powder bed fusion

PurposeSelective laser melting and electron beam melting processes are well-known for the additive manufacturing of metal parts. Metal powder bed fusion (MPBF) is a common term for them. The MPBF process can empower the manufacturing of intricate shapes by reducing the use of special tools, shortening the supply chain and allowing small batches. However, the MPBF process suffers from many quality issues. In literature, several works are recorded for qualification of the MPBF part. The purpose of this study is to recollect those works done for quality control and report their helpful findings for further research and development.Design/methodology/approachA systematic literature review was conducted to highlight the major quality issues in the MPBF process and its root causes. Further, the works reported in the literature for mitigation of these issues are classified and discussed in five categories: experimental investigation, finite element method-based numerical models, physics-based analytical models, in-situ control using artificial intelligence (AI) and machine learning (ML) methods and statistical approaches. A comparison is also prepared among these strategies based on their suitability and limitations. Additionally, improvements in MPBF printers are pointed out to enhance the part quality.FindingsAnalytical models require less computational time to simulate the MPBF process and need a smaller number of experiments to confirm the results. They can be used as an efficient process parameter planning tool to print metal parts for noncritical applications. The AI-ML based quality control is also suitable for MPBF processes as it can control many processing parameters that may affect the quality of the MPBF part. Moreover, capabilities of MPBF printers like thinner layer thickness, smaller beam diameter, multiple lasers and high build temperature range can help in quality control.Research limitations/implicationsThis study converts the piecemeal data on MPBF part qualification methods into interesting information and presents it in tabular form under each strategy. This tabular information provides the basis for further quality improvement efforts in the MPBF process.Originality/valueThis study references researchers and practitioners on recent quality control efforts and their significant findings for a better quality of MPBF part.

Saturation pressure of nonequilibrium titanium evaporation during additive manufacturing by electron powder bed fusion

Electron beam powder bed fusion (E-PBF) is an attractive technology for the additive manufacturing of metal parts. However, process improvements require precise control of the energy transferred to the powder by the electron beam. Here, we used tunable diode laser absorption spectroscopy (TD-LAS) to measure the velocity distribution functions of titanium atoms evaporated during E-PBF. The narrow spectral ranges emitted by laser diodes allow for high-resolution absorption profiles of the evaporated atoms and thus accurate determinations of their Doppler broadening, density, and temperature during melting. The obtained vapor temperature reveals overheating at the surface of the melt pool relative to the low-pressure (0.1 Pa) boiling point of titanium, indicating that evaporation occurs under nonequilibrium conditions. We characterized the influence of the linear energy density on titanium evaporation and found it to be consistent with the saturation vapor pressure. Our characterization of the vapor properties provides reliable inputs for melt pool simulations. Furthermore, TD-LAS may be further exploited to prevent the evaporation of low-concentration alloy elements, which can induce defects in the printed part.

A new approach for calculating inherent strain and distortion in additive manufacturing of metal parts

Additive manufacturing (AM) of metallic parts is widely utilized for industrial applications. However, quality issues of the printed parts, including part distortion and cracks caused by high temperature and fast cooling, result in high residual stress. This is a challenge that limits the industry acceptance of AM. To overcome this challenge, a numerical modeling method for predicting part distortion at the design stage plays an important role and enables design engineers to remove failures before printing as well as determine the optimal printing process parameters to minimize part deformation. This research proposes an inherent strain-based part deformation prediction method. To determine the inherent strain (IS) value, a micro-scale model for analyzing the temperature distribution is constructed. The IS value is calculated from the temperature gradient. Then, the IS value is used for determining the part deformation. The proposed methodology has been developed and evaluated using a 316L stainless steel cantilever beam in both simulations and experimental results.

A review of hybrid additive manufacturing of metal parts

This article provides an overview of the latest developments in the field of hybrid additive manufacturing of metal parts. The concept and various kinds of additive manufacturing are discussed. Special attention is paid to hybridization of additive technologies and various processes of forming: die forging, deep drawing, and others. The background and significance of the technologies, as well as their applicability in production are presented. The combination of additive manufacturing with forming processes is carried out with a dual purpose: to expand the area of application of additive manufacturing and overcome its limitations associated with low productivity, metallurgical defects, surface roughness and lack of dimensional accuracy; new application of traditional forming processes.

What is the economic feasibility of manufacturing a metal-metal- polymer composite part compared to other technologies?

ABSTRACT The purpose of the article is to analyse the manufacturing factors that affect the cost of manufacturing a part. Nowadays the cost of equipment used for metal 3D printing, as well as metal powders, are still very expensive. The cost of additive manufacturing of metal parts is mainly dependent on the volume of printing, therefore, reducing the volume of printing can lead to a significant reduction in the cost of manufacturing the part. Manufacturing of a metal shell, the cavity of which is filled with a cheap metal polymer, can be an excellent alternative to an all-metal part. The article provides a method for calculating the cost of manufacturing a lever part using various technologies: subtractive, additive, and composite part manufacturing technology. According to the calculated data, the dependence of the cost of manufacturing a part on piece time has been built, which can be interpreted as the amount of machining. The constructed linear dependence can give an idea of the effectiveness of the application of a particular technology for obtaining a part. In addition, non-economic factors affecting the possibility of using various technological processes for manufacturing a part are described.

Characterizing the strength of support-model connection in the case of laser powder bed fusion technology by torsion test

Additive manufacturing of metal parts was investigated in this research work, which connects to the models' supports. The connection between the support and the model has a high impact on the mechanical fixturing, the heat conduction, the removability of the support and the success of printing. In this research work, some support and tooth parameters such as the top length, the hatch distance, and Z offset were investigated to create a model-support connection strength map. This knowledge makes it possible to select the most appropriate connection type between the support and the model by the requirements specified in different cases. The strength of the support-model connection was characterized by the shearing properties using the torsion test. The results are illustrated and compared by different support parameters and materials. The 316L stainless steel and Ti6Al4V alloy were investigated. Different failure modes were determined depending on the chosen parameters.

Data-driven analysis of process, structure, and properties of additively manufactured Inconel 718 thin walls

In additive manufacturing of metal parts, the ability to accurately predict the extremely variable temperature field in detail, and relate it quantitatively to structure and properties, is a key step in predicting part performance and optimizing process design. In this work, a finite element simulation of the directed energy deposition (DED) process is used to predict the space- and time-dependent temperature field during the multi-layer build process for Inconel 718 walls. The thermal model results show good agreement with dynamic infrared images captured in situ during the DED builds. The relationship between predicted cooling rate, microstructural features, and mechanical properties is examined, and cooling rate alone is found to be insufficient in giving quantitative property predictions. Because machine learning offers an efficient way to identify important features from series data, we apply a 1D convolutional neural network data-driven framework to automatically extract the dominant predictive features from simulated temperature history. Very good predictions of material properties, especially ultimate tensile strength, are obtained using simulated thermal history data. To further interpret the convolutional neural network predictions, we visualize the extracted features produced on each convolutional layer and compare the convolutional neural network detected features of thermal histories for high and low ultimate tensile strength cases. A key result is the determination that thermal histories in both high and moderate temperature regimes affect material properties.

ОЦЕНКА ЭКОНОМИЧЕСКОЙ ЭФФЕКТИВНОСТИ ТЕХНОЛОГИИ ИЗГОТОВЛЕНИЯ КОМПОЗИТНЫХ МЕТАЛЛ-МЕТАЛЛОПОЛИМЕРНЫХ ДЕТАЛЕЙ В СРАВНЕНИИ С АДДИТИВНОЙ И СУБТРАКТИВНОЙ ТЕХНОЛОГИЯМИ

The development of additive manufacturing leads to the emergence of new 3D printing technologies, new materials for 3D printing and a gradual reduction in the cost of production. Nowadays, the cost of equipment used for metal and metal powders 3D printing are still very expensive. This factor makes the production technologies unavailable for the civil engineering industry in the manufacture of functional parts. The cost of additive manufacturing of metal parts is mainly dependent on the volume of printing. Reducing the print volume can lead to a significant reduction in the cost of manufacturing the part. Fabrication of a metal shell, the cavity of which is filled with a cheap metal polymer, can be an excellent alternative to an all-metal part. Such a metal-metal-polymer composite part can have sufficient strength and significantly lower cost. However, there are no dependencies today to understand the economic efficiency of using a particular production technology. The article provides a method for calculating the cost of manufacturing a lever part using various technologies: subtractive, additive and composite part manufacturing technology. According to the calculated data, the dependence of the cost of manufacturing a part on piece time is built. It can be interpreted as the amount of machining. The constructed linear dependence can give an idea of the effectiveness of the application of a particular technology for obtaining a part. In addition, non-economic factors affecting the possibility of using various technological processes for manufacturing a part are described. Together, the presented data allow the technologist to comprehensively assess the possibility of effective application of a particular production technology and make an appropriate informed decision.

COMPUTATIONAL JUSTIFICATION OF THE USE OF COMPOSITE METAL-METAL POLYMER PARTS IN THE PRODUCTION OF FUNCTIONAL STRUCTURES

Additive manufacturing of metal parts occupies an increasing number of areas of mechanical engineering, but still remains too expensive for mass use. Based on the experience in the production of combined metal-metal polymer forming parts of molds, a new method for the production of composite parts from a metal shell filled with metal polymer is proposed. The strength calculations by the finite element method of the exoskeleton part and a sample of simplified geometry are given as the basis of the study. A comparison of the strength characteristics of parts made of various materials and their combinations showed high strength characteristics of a composite part made of a metal shell and a metal polymer filler. The metal-metal polymer composite part is distinguished not only by its high strength, but also by a significantly lower cost due to the reduction in the volume of 3D printing with metal. The article substantiates the main problems facing researchers and technologists in the development of a practically applicable technology for producing such composite parts.