Thermometric investigations for the characterization of fatigue crack initiation and propagation in Wire and Arc Additively Manufactured parts with as-built surfaces

Metal Additive Manufacturing (AM) allows for the fabrication of complex shapes with high added value at low costs. Indeed, as-built structures are near net shape: they require few to no finishing operations. However, as-built AM parts present significant roughness caused by the layer discretization. In the case of the Wire and Arc Additive Manufacturing (WAAM) process, used for large-scale structures, the as-built roughness is estimated to several hundreds of micrometers. For complex geometries, a complete machining of the surfaces is not necessarily possible. In this study, an experimental method is proposed, relying on thermoelastic stress analysis, to characterize the effect of as-built WAAM surface roughness on high-cycle fatigue properties. Using an infrared camera, multiple cracks can be detected and monitored over a large surface on rough WAAM samples under cyclic bending. The collected data constitutes valuable information for the identification of a fatigue model dedicated to as-built WAAM structures.     

Residual stress of as-deposited and rolled wire+arc additive manufacturing Ti–6Al–4V components

Wire + arc additive manufacturing components contain significant residual stresses, which manifest in distortion. High-pressure rolling was applied to each layer of a linear Ti–6Al–4V wire + arc additive manufacturing component in between deposition passes. In rolled specimens, out-of-plane distortion was more than halved; a change in the deposits' geometry due to plastic deformation was observed and process repeatability was increased. The Contour method of residual stresses measurements showed that although the specimens still exhibited tensile stresses (up to 500?MPa), their magnitude was reduced by 60%, particularly at the interface between deposit and substrate. The results were validated with neutron diffraction measurements, which were in good agreement away from the baseplate.

This paper is part of a Themed Issue on Measurement, modelling and mitigation of residual stress.     

Thermo-mechanical analysis of Wire and Arc Additive Layer Manufacturing process on large multi-layer parts

Wire and Arc Additive Layer Manufacturing (WAALM) is gaining increasing popularity as the process allows the production of large custom-made metal workpieces with high deposition rates. The high power input of the welding process, causes significant residual stress and distortion of the workpiece. This paper describes the thermo-mechanical behaviour of the multi-layer wall structure made by the WAALM process. A 3D thermo-elastic–plastic transient model and a model based on an advanced steady-state thermal analysis are employed in this study. This modelling approach shows a significant advantage with respect to the computational time. The temperature simulations and distortion predictions are verified by comparing with the experimental results from thermo-couples and laser scanners, while the residual stresses are verified with the neutron diffraction strain scanner ENGIN-X. The stress across the deposited wall is found uniform with very little influence of the preceding layers on the following layers. The stress redistributed after unclamping with a much lower value at the top of the wall than at the interface due to the bending distortion of the sample.     

电弧增材制造技术及其在TC4钛合金中的应用研究进展

增材制造是于20世纪80年代中期发展起来的一门新兴技术,因能快速精确地制造出形状复杂的结构件而受到广泛关注。电弧增材制造是以电弧为热源,采用逐层堆焊的方式制造出致密的金属构件,具有制造成本低廉、成形效率高的突出特点,在大尺寸、复杂零件的快速成形技术中表现出明显的优势,因而在航空航天、汽车船舶等领域有广阔的应用前景。TC4的化学活性高、热导率低、强度高,具有优异的综合力学性能,是应用最广泛的钛合金。TC4并不适合采用传统的加工方法制备,因此采用电弧增材制造的方法成形TC4结构件。但成形件典型的宏观组织为外延生长的柱状晶,导致其力学性能存在各向异性。本文综述了电弧增材制造的发展历史,结合该技术的特征及国内外研究现状,介绍了电弧增材制造TC4钛合金成形件的组织及性能方面的研究进展。     

On the bottleneck of adopting 3D printing in manufacturing

A timely book, titled ‘Standards, Quality Control, and Measurement Sciences in 3D Printing and Additive Manufacturing’ has been published to discuss the bottleneck issues when adopting 3D printing in manufacturing. This book review provides some personal thoughts and discussions on the new book.     

Fracture toughness and fatigue crack growth rate properties in wire + arc additive manufactured Ti‐6Al‐4V

This paper presents an experimental investigation of the fracture and fatigue crack growth properties of Ti‐6Al‐4V produced by the Wire + Arc Additive Manufacture (WAAM®) process. First, fracture toughness was measured for two different orientations with respect to the build direction; the effect of wire oxygen content and build strategy were also evaluated in the light of microstructure examination. Second, fatigue crack growth rates were measured for fully additive manufactured samples, as well as for samples containing an interface between WAAM® and wrought materials. The latter category covers five different scenarios of crack location and orientation with respect to the interface. Fatigue crack growth rates are compared with that of the wrought or WAAM® alone conditions. Crack growth trajectory of these tests is discussed in relation to the microstructure characteristics.     

Design By Additive Manufacturing: an application in aeronautics and defence

Additive Manufacturing (AM) is a major challenge for the deployment of Industry 4.0 in companies. Thus, it becomes essential to control the potential contributions of this innovative process from the early stages of design. In this paper, previous Design and Creativity For/With/Through AM approaches are first reviewed comprehensively and classified into distinct categories according to their main purpose and application. Then, they are integrated into a modular framework as part of a global 5-step design approach to promote AM in the whole design process: the Design By Additive Manufacturing (DBAM) methodology. A validation of the method is then proposed on an industrial case study from the aeronautics and defence sector, thereby fostering the complete exploitation of AM potentials and the development of AM-conformal designs.     

Numerical and experimental assessment of the mechanical properties of 3D printed 18-Ni300 steel trabecular structures produced by Selective Laser Melting – a lean design approach

ABSTRACT

Lattice and trabecular structures are excellent candidates for energy absorbing applications such as personal protective equipment or any sort of bumper. Additive manufacturing technologies allow more freedom in the design of new topologies such as trabecular and lattice structures overcoming the limitation of the traditional manufacturing processes. In the present research, an investigation on the ductile behaviour of additive structures is presented. In a first phase, a series of 18-Ni300 steel specimens with different geometries has been printed using the SLM (Selective Laser Melting) technology. Experimental quasi-static tests on those samples were numerically reproduced, in order to retrieve the actual stress state, quantify the plastic strain at failure and calibrate a ductile damage model. In a second phase, trabecular structures, made of the same material and processed with the same technology as the samples, were produced and experimentally tested in a compression test. Simulations including the calibrated model were used to reproduce the response of the elementary trabecular cell subjected to different loading conditions (micro-scale simulations). This kind of simulations is very time-consuming and not suitable for the design/optimisation of large structures made by thousands of elementary cells. To overcome this limitation, in a third phase of the project, an effective and efficient design methodology has been implemented. Each elementary cell is modelled as an equivalent non-linear three-dimensional spring. The force–displacement (torque–rotation) relations in different directions were obtained with the previously described micro-scale FE simulations. In this manner, the computational costs can be reduced by many orders of magnitude allowing the study of complex real systems.     

Failure In metal honeycombs manufactured by selective laser melting of 304 L stainless steel under compression

ABSTRACT

Cellular structures, specifically honeycombs, are commonly used as core materials in sandwich structures. This is especially true in aerospace applications where high bending and out-of-plane compressive stiffness coupled with low component weight is required. Additive manufacturing techniques are well suited for the manufacture of such cellular structures in a cost-effective manner. The current work focuses on honeycombs using selective laser melting of 304?L stainless steel. The mechanical behaviour of honeycombs was evaluated using out-of-plane compression tests. A numerical model was built to describe failure of the additively manufactured honeycombs. Compression tests were performed, on cylindrical samples to build the nonlinear material model. The material behaviour was found to be dependent on the build direction. Results of experiments and simulation show that failure occurs through a plastic buckling mechanism.     

Complex metallic alloys as new materials for additive manufacturing

Additive manufacturing processes allow freeform fabrication of the physical representation of a three-dimensional computer-aided design (CAD) data model. This area has been expanding rapidly over the last 20 years. It includes several techniques such as selective laser sintering and stereolithography. The range of materials used today is quite restricted while there is a real demand for manufacturing lighter functional parts or parts with improved functional properties. In this article, we summarize recent work performed in this field, introducing new composite materials containing complex metallic alloys. These are mainly Al-based quasicrystalline alloys whose properties differ from those of conventional alloys. The use of these materials allows us to produce light-weight parts consisting of either metal–matrix composites or of polymer–matrix composites with improved properties. Functional parts using these alloys are now commercialized.     

Microstructural characterization and mechanical integrity of stainless steel 316L clad layers deposited via wire arc additive manufacturing for nuclear applications

The potential applications of stainless steel 316L components using wire arc additive manufacturing offers many benefits such as improved part complexity, higher deposition rate and less material waste. Microstructural examination indicates the strong interlayer bonding between cladded layers and was mainly austenitic with columnar and equiaxed dendrites while equiaxed grains with annealing twins were observed in the stainless steel 316L substrate. In the current study, we report that stainless steel 316L additively cladded via wire arc additive manufacturing exhibits a 11 % and 14 % increase in the yield strength and tensile strength, correspondingly in contrast to the stainless steel 316L substrate. The enhanced mechanical properties are attributed to the columnar structure and interlayer remelted peritectic growth. Hardness values were higher at the cladded layers compared to the interface and substrate. Interface sample failed in the substrate side and all samples exhibited ductile mode of fracture with fine dimples and micro voids. Wire arc additive manufacturing process can be employed for producing or repairing components with better mechanical properties and corrosion performance for elevated temperature environments including nuclear reactor applications.     

Thin wall tubes with Fe3Al/SS316L graded structure obtained by using laser engineered net shaping technology

In the present paper, designing, technological and material aspects of the Laser Engineered Net Shaping (LENS) manufacturing process of functionally graded materials (FGMs) components based on the Fe–Al intermetallic alloys, have been described in details. The presented results are divided into two parts as follows: in the first part a model and a LENS manufacturing process of the selected FGMs component (the Fe₃Al/314L steel tube) have been developed. In the second part, an experimental verification of the model and the process has been carried out. It is shown that, automatically generated code does not allow programming variation of the chemical composition perpendicularly to the wall of the tube. However, applied modification of the code results in a successive direct fabrication of the 316L/Fe₃Al FGM tubes. Directly fabricated FGM tubes were characterized by a smooth transition between both components (the 316L steel and the Fe₃Al alloy), a high metallurgical quality and a good reproduction of the designed model’s shape.     

Architectured bimetallic laminates by roll bonding: bonding mechanisms and applications

Abstract

Manufacturing of bimetallic laminates (<2 mm) with an internal architecture by roll bonding allows to obtain a compromise of conflicting properties. Two applications are considered: copper–steel–copper sheets for high power electronic component substrates and lightweight aluminium–steel–aluminium laminates for structural, electromagnetic applications in power generation and for electromagnetic compatibility. They have in common an architecture, with three-dimensional percolating networks of two metals produced with a sufficient precision. The bonding mechanisms are investigated through microstructural and thermomechanical characterisation of the assemblies produced. Roll bonding fills the voids in a central component by plastic deformation and creates the bonds by cold welding. It may be followed or preceded by surface and heat treatments with the objective to improve the cold welding and to relieve the internal stress state. Architectural rules to optimise the properties of the two-phase laminates in view of the applications may be guided by finite element models combining physical and thermomechanical aspects.     

Obtaining uniform deposition with variable wire feeding direction during wire-feed additive manufacturing

Wire-feed additive manufacturing is cost competitive and efficient in producing large and complex components in aerospace applications. However, for the additive manufacturing technologies with lateral wire feeding, including laser wire additive manufacturing, electron beam freeform fabrication, plasma arc welding, and gas tungsten arc welding, it is difficult to obtain uniform deposit due to the variable wire feeding direction. In this work, high-angle wire feeding method is proposed to obtain uniform deposit in gas tungsten arc welding-based additive manufacturing. The results illustrate that low wire feeding angle (30°–50°) causes the deposition to break at the back feeding, meanwhile too high wire feeding angle (70°) leads to many littered droplets on one side of the deposition at the condition of side feeding. A uniform deposition can be obtained at the optimal wire feeding angle of 60° in any wire feeding direction, and the reasons have been discussed based on the temperature distribution characteristics of the arc and molten pool. Furthermore, the deposition layers exhibit similar columnar prior β grains, basketweave microstructure, and tensile properties from different wire feeding directions.     

电弧增材制造技术及其应用的研究进展

电弧增材制造是近年来发展最为迅速的增材制造技术之一,其以电弧为热源,通过熔化金属丝材,在规划的路径上层层堆积成形三维实体金属构件,具有制造成本低、制造自由度与成形效率高等优点,尤其适用于大型尺寸及中低结构复杂度金属构件的形性一体化成形.近年来,电弧增材制造技术在国内外得到了广泛研究与长足发展,在电弧增材制造装备、过程控...     

Porosity,cracks, and mechanical properties of additively manufactured tooling alloys: a review

Additive manufacturing (AM) technologies are currently employed for the manufacturing of completely functional parts and have gained the attention of high-technology industries such as the aerospace, automotive, and biomedical fields. This is mainly due to their advantages in terms of low material waste and high productivity, particularly owing to the flexibility in the geometries that can be generated. In the tooling industry, specifically the manufacturing of dies and molds, AM technologies enable the generation of complex shapes, internal cooling channels, the repair of damaged dies and molds, and an improved performance of dies and molds employing multiple AM materials. In the present paper, a review of AM processes and materials applied in the tooling industry for the generation of dies and molds is addressed. AM technologies used for tooling applications and the characteristics of the materials employed in this industry are first presented. In addition, the most relevant state-of-the-art approaches are analyzed with respect to the process parameters and microstructural and mechanical properties in the processing of high-performance tooling materials used in AM processes. Concretely, studies on the AM of ferrous (maraging steels and H13 steel alloy) and non-ferrous (stellite alloys and WC alloys) tooling alloys are also analyzed.The full text can be downloaded at https://link.springer.com/article/10.1007/s40436-021-00365-y     

Failure analysis of cracking in wheel rims – material and manufacturing aspects

Manufacturing of wheel in automotive industries demands no-flaw wheels. However, process as well as material deficiency in varying ratios of influence has been the counteracting factors in producing flawless wheel components. Tube and tubeless wheels for light and medium commercial vehicles are manufactured by cold forming of slit hot rolled strips from low carbon steel with or without micro alloying. During manufacturing and forming of the strips, cracking of wheel rims is a major problem at the production line. The paper discusses about one of the failure types in wheel rims, where the wheel rim thins down locally and cracks at the weld.     

3D printing of smart materials: A review on recent progresses in 4D printing

ABSTRACT

Additive manufacturing (AM), commonly known as three-dimensional (3D) printing or rapid prototyping, has been introduced since the late 1980s. Although a considerable amount of progress has been made in this field, there is still a lot of research work to be done in order to overcome the various challenges remained. Recently, one of the actively researched areas lies in the additive manufacturing of smart materials and structures. Smart materials are those materials that have the ability to change their shape or properties under the influence of external stimuli. With the introduction of smart materials, the AM-fabricated components are able to alter their shape or properties over time (the 4th dimension) as a response to the applied external stimuli. Hence, this gives rise to a new term called ‘4D printing’ to include the structural reconfiguration over time. In this paper, recent major progresses in 4D printing are reviewed, including 3D printing of enhanced smart nanocomposites, shape memory alloys, shape memory polymers, actuators for soft robotics, self-evolving structures, anti-counterfeiting system, active origami and controlled sequential folding, and some results from our ongoing research. In addition, some research activities on 4D bio-printing are included, followed by discussions on the challenges, applications, research directions and future trends of 4D printing.     

Using Big Area Additive Manufacturing to directly manufacture a boat hull mould

ABSTRACT

Big Area Additive Manufacturing (BAAM) is a large-scale, 3D printing technology developed by Oak Ridge National Laboratory's Manufacturing Demonstration Facility and Cincinnati, Inc. The ability to quickly and cost-effectively manufacture unique moulds and tools is currently one of the most significant applications of BAAM. This work details the application of a BAAM system to fabricate a 10.36?m (34?ft) catamaran boat hull mould. The goal of this project was to explore the feasibility of using BAAM to directly manufacture a mould without the need for thick coatings. The mould was printed in 12 individual sections over a five-day period. After printing, the critical surfaces of the mould were CNC-machined, the sections were assembled, and a final hull was manufactured using the mould. The success of this project illustrates the time and cost savings of BAAM in the fabrication of large moulds.     

Mechanical properties of titanium-based Ti–6Al–4V alloys manufactured by powder bed additive manufacture

Additive manufacturing is currently a topic of considerable interest at both academic and industrial levels. While a significant amount of data exists on the mechanical properties and structure–property relationships of traditional wrought alloys, less information is available on alloys manufactured by additive manufacture. This review examines current state-of-the-art manufacture of titanium-based Ti–6Al–4V alloys by powder bed additive manufacture. Published mechanical properties to date are collected which include tensile strength, yield strength, hardness, wear, fracture toughness and fatigue. Differences in microstructure and properties compared to conventional wrought alloys of the same composition are described.