Laser-based additive manufacturing opens up a new horizon in terms of processing novel alloys that are difficult to process using conventional techniques. Selective laser melting (SLM) is a powder ...bed fusion type additive manufacturing (AM) process, for fabricating metallic parts where powder particles are fused using a high energy laser beam as a thermal source. Although SLM is widely used for manufacturing end-use metal tools and components, it requires careful tailoring of a range of parameters (e.g. layer thickness, laser spot size, laser power, hatch spacing, scanning strategy, etc.) to achieve the required densification, microstructures, and mechanical properties. Therefore, there is a critical need to systematically investigate the effect of these processing parameters on densification, microstructures and mechanical properties of materials. In this research work, 16 samples fabricated by SLM process with varying processing parameters have been investigated. We have studied the effect of scanning speed, scanning strategy, and energy density on microstructure and mechanical properties of these samples by performing microhardness tests, tensile tests, and a scanning electron microscopy (SEM) analysis. We have concluded that samples fabricated with alternate hatches and single pass of a laser beam exhibited highest densification and most refined microstructure. Furthermore, samples processed at higher scanning speeds had better densification, as well as excellent mechanical properties. We have also observed an increase in the width of dendrites as a result of decreasing the scanning speed primarily due to decrease in cooling rate.
•Failure analysis of new complex equipment is important but difficult.•We propose a recursive method to perform such failure analysis.•The same analyses are performed at three different levels in the ...system structure.•At each level, both an FTA (completeness) and an FMEA (prioritization) are performed.•In a case study, the method turns out to be efficient and effective.
When designing a maintenance programme for a capital good, especially a new one, it is of key importance to accurately understand its failure behaviour. Failure mode and effects analysis (FMEA) and fault tree analysis (FTA) are two commonly used methods for failure analysis. FMEA is a bottom-up method that is less structured and requires more expert knowledge than FTA, which is a top-down method. Both methods are time-consuming when applied thoroughly, which is why in many cases, they are not applied at all. We propose a method in which both are used in a recursive manner: First, a system level FTA is performed, which results in a set of failure modes. Using FMEA, the criticality of the failure modes is assessed in order to select only the critical system level failure modes. For each of those, a function level FTA is performed, followed by an FMEA. Finally, a component level FTA and FMEA are performed on the critical function level failure modes. We apply our method to a recently developed additive manufacturing system for metal printing, the MetalFAB1 of Additive Industries (AI), and find that the engineers at AI consider the method to be efficient and effective.
Wire arc additive manufacturing (WAAM) features advantages such as low cost and high disposition rate, and thus WAAM is a feasible additive manufacturing process. Although some characteristics of ...WAAM have been documented in the literature, the process stability, structural integrity, component morphology, microstructure, and mechanical properties during WAAM under different arc modes are not comprehensively demonstrated and understood. Here, we performed WAAM experiments with 316L stainless steel under different arc modes and a constant deposition rate, and then we discussed the mechanism and impact of the arc mode on the manufacturing process stability, structural integrity, microstructures, and mechanical properties. The results indicate that the SpeedPulse and SpeedArc additive manufacturing processes are relatively stable, significantly efficient, and structurally sound. Although the deposition rate and scanning speed of SpeedPulse WAAM and SpeedArc WAAM are the same, SpeedArc WAAM has a lower heat input and a higher cooling rate. Therefore, SpeedArc WAAM produces a finer solidification structure than SpeedPulse WAAM. The ultimate tensile strengths of the SpeedPulse and SpeedArc additive manufactured specimens along the horizontal direction are greater than 540 MPa and slightly greater than previously reported results. Due to the lower heat input and finer solidification structure, a component produced by SpeedArc WAAM has greater tensile strength and hardness than a component produced by SpeedPulse WAAM.
Nowadays, there is a great manufacturing trend in producing higher quality net-shape components of challenging geometries. One of the major challenges faced by additive manufacturing (AM) is the ...residual stresses generated during AM part fabrication often leading to unacceptable distortions and degradation of mechanical properties. Therefore, gaining insight into residual strain/stress distribution is essential for ensuring acceptable quality and performance of high-tech AM parts. This research is aimed at comparing microstructure and residual stress built-up in Ti–6Al–4V AM components produced by Wire+Arc Additive Manufacturing (WAAM) and by laser cladding process (CLAD).
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•The highest residual stress values are in longitudinal (deposition) direction•The maximum stress is observed in between baseplate and the deposited wall•CLAD sample show lower residual stress than WAAM sample•Both specimens exhibit columnar grains with finer wavy morphology in CLAD•Compressive stress is observed in different regions depending on the process
•Effects of defects, surface roughness and HIP on the fatigue strength of a Ti6Al4V by AM were studied.•HIP improved fatigue strength to the level of ideal fatigue limit if surface roughness is ...removed.•Evaluating method for the effective size √areaeffmax of irregularly shaped defects was proposed.•AM fatigue design method was proposed with the √area parameter model and the statistics of extremes.
The additive manufacturing (AM) is expected to be a promising manufacturing process for high strength or hard steels such as Ti-6Al-4V for the aerospace industry components having complex shapes. However, disadvantage or challenge of AM is presence of defects which are inevitably contained in the manufacturing process. This paper focuses on the effects of defects, surface roughness and Hot Isostatic Pressing (HIP) process on the fatigue strength of a Ti-6Al-4V manufactured by AM. Defects were mostly gas pores and those made by lack of fusion. Many defects which were formed at subsurface were eliminated by HIP and eventually HIP improved fatigue strength drastically to the level of the ideal fatigue limit to be expected from the hardness. Surface roughness had strong detrimental influence on fatigue strength. The method for estimating the effective size √areaeffmax of irregularly shaped defects and interacting adjacent defects was proposed from the viewpoint of fracture mechanics.
This paper provides an overview on the main additive manufacturing/3D printing technologies suitable for many satellite applications and, in particular, radio-frequency components. In fact, nowadays ...they have become capable of producing complex net-shaped or nearly net-shaped parts in materials that can be directly used as functional parts, including polymers, metals, ceramics, and composites. These technologies represent the solution for low-volume, high-value, and highly complex parts and products.
Additive manufacturing has revolutionized the manufacturing paradigm in recent years due to the possibility of creating complex shaped three-dimensional parts which can be difficult or impossible to ...obtain by conventional manufacturing processes. Among the different additive manufacturing techniques, wire and arc additive manufacturing (WAAM) is suitable to produce large metallic parts owing to the high deposition rates achieved, which are significantly larger than powder-bed techniques, for example. The interest in WAAM is steadily increasing, and consequently, significant research efforts are underway. This review paper aims to provide an overview of the most significant achievements in WAAM, highlighting process developments and variants to control the microstructure, mechanical properties, and defect generation in the as-built parts; the most relevant engineering materials used; the main deposition strategies adopted to minimize residual stresses and the effect of post-processing heat treatments to improve the mechanical properties of the parts. An important aspect that still hinders this technology is certification and nondestructive testing of the parts, and this is discussed. Finally, a general perspective of future advancements is presented.
In this paper, a generic method based on fuzzy aggregation operator for multi-criterion decision-making problems in design for additive manufacturing is proposed. Firstly, a fuzzy power weighted ...Maclaurin symmetric mean operator based on Hamacher T-norm and T-conorm is constructed via a combination of fuzzy numbers, power average operator, weights, Maclaurin symmetric mean operator, and operational rules of fuzzy numbers based on Hamacher T-norm and T-conorm. Based on the constructed operator, a generic method for solving the multi-criterion decision-making problems in design for additive manufacturing is then developed. After that, an example of additive manufacturing machine and material selection and an example of optimal build direction selection are introduced to illustrate the developed method. Finally, a set of numerical experiments are reported to demonstrate the effectiveness and capabilities of the method. The demonstration results suggest that the method can effectively solve a multi-criterion decision-making problem in design for additive manufacturing and has the characteristics in considering the interactions of criteria, reducing the effect of noise criterion values, and capturing the risk attitude of decision-makers.
Functionally graded conformal lattice structures (FGCLSs) are a particular type of lattice structure in which lattice unit cells are populated following structural boundaries and the density of the ...lattice unit cells is optimally distributed. Additionally, additively manufactured parts are reported to have anisotropic mechanical properties that highly depend on the part build orientations. This is extremely important in designing FGCLS parts where orientations of lattice unit cells are not uniform, making the build orientation selection more challenging. In this study, a concurrent density distribution and build orientation optimization framework of additively manufactured FGCLSs for structure-performance maximization was developed. The proposed approach was validated via case studies on lightweight part design for compliance minimization, with three design examples having geometric complexity levels varying from low to high. The results showed that the proposed concurrent optimization method was more effective at enhancing structural performance than optimizing only the density distribution of the structure. In addition, the build orientation configurations determined by the proposed method provided better structural performance compared to those determined using other slicing software. Moreover, compared to the pseudo-worst build orientation configuration, the configuration obtained from the proposed approach could enhance structural performance by up to 47.56%.
•A concurrent structure–process optimum part design with conformal lattice structure.•Euler’s angle was applied for build orientation modeling.•Build orientation dependent anisotropic lattice scaling law was developed.•Density distribution (structure) and build orientation (process) are concurrently optimized.
High entropy alloys (HEAs) have attracted much attention and been considered as novel materials with wide application prospects due to their outstanding comprehensive properties. With the development ...of laser processing technology, laser additive manufacturing (LAM) is regarded as a particularly feasible way to fabricate high entropy alloys. In this study, a relatively dense equiatomic FeCrCoMnNi high entropy alloy with excellent mechanical properties is manufactured by LAM successfully. Effect of heat treatment on phase, microstructure, microhardness, residual stress and mechanical properties of as-built (AB) specimens are investigated. The results show that the AB specimen exhibits a single FCC solid solution with mixed epitaxial grown dendrite columnar grain and equiaxed grain microstructure. After heat treatment, the dendritic microstructure of AB specimen evolves into recrystallized grain structure of HT-1100 specimen (heat treated at 1100 °C), while the crystalline structure is hardly changed. The AB specimen exhibits a superior microhardness and mechanical properties to that of the corresponding arc-melting specimen. The HTed specimen has much higher ductility than that of the AB specimen without distinct sacrifice of strength.
•A relatively dense FeCrCoMnNi HEA is manufactured by LAM.•The LAMed specimen exhibits a single FCC solid solution with non-equilibrium microstructure.•The LAMed specimen has excellent microhardness and mechanical properties.•Heat treatment can improve the ductility of LAMed specimen without distinct sacrifice of strength.
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