Microstructure of interpass rolled wire + arc additive manufacturing Ti-6Al-4V components

Mechanical property anisotropy is one of the issues that are limiting the industrial adoption of additive manufacturing (AM) Ti-6Al-4V components. To improve the deposits’ microstructure, the effect of high-pressure interpass rolling was evaluated, and a flat and a profiled roller were compared. The microstructure was changed from large columnar prior beta grains that traversed the component to equiaxed grains that were between 56 and 139 μm in size. The repetitive variation in Widmanstätten alpha lamellae size was retained; however, with rolling, the overall size was reduced. A “fundamental study” was used to gain insight into the microstructural changes that occurred due to the combination of deformation and deposition. High-pressure interpass rolling can overcome many of the shortcomings of AM, potentially aiding industrial implementation of the process.EPSRC, AirBu

The effectiveness of combining rolling deformation with wire-arc additive manufacture on β-Grain refinement and texture modification in Ti-6Al-4V

In Additive Manufacture (AM), with the widely used titanium alloy Ti–6Al–4V, the solidification conditions typically result in undesirable, coarse-columnar, primary β grain structures. This can result in a strong texture and mechanical anisotropy in AM components. Here, we have investigated the efficacy of a new approach to promote β grain refinement in Wire–Arc Additive Manufacture (WAAM) of large scale parts, which combines a rolling step sequentially with layer deposition. It has been found that when applied in-process, to each added layer, only a surprisingly low level of deformation is required to greatly reduce the β grain size. From EBSD analysis of the rolling strain distribution in each layer and reconstruction of the prior β grain structure, it has been demonstrated that the normally coarse centimetre scale columnar β grain structure could be refined down to < 100 μm. Moreover, in the process both the β and α phase textures were substantially weakened to close to random. It is postulated that the deformation step causes new β orientations to develop, through local heterogeneities in the deformation structure, which act as nuclei during the α → β transformation that occurs as each layer is re-heated by the subsequent deposition pass

Defining next-generation additive manufacturing applications for the Ministry of Defence (MoD)

“Additive Manufacturing” (AM) is an emerging, highly promising and disruptive technology which is catching the attention of the Defence sector due to the versatility it is offering. Through the combination of design freedom, technology compactness and high deposition rates, technology stakeholders can potentially exploit rapid, delocalized and flexible production. Having the capability to produce highly tailored, fully dense, potentially optimized products, on demand and next to the point of use makes this emerging and immature technology a game changer in the “Defence Support Service” (DS2) sector. Furthermore, if the technology is exploited for the Royal Navy, featured with extended and disrupted supply chains, the benefits are very promising. While most of the AM research and efforts are focusing on the manufacturing/process and design opportunities/topology optimization, this paper aims to provide a creative but educated and validated forecast on what AM can do for the Royal Navy in the future. This paper aims to define the most promising next generation Additive Manufacturing applications for the Royal Navy in the 2025 – 2035 decade. A multidisciplinary methodology has been developed to structure this exploratory applied research study. Moreover, different experts of the UK Defence Value Chain have been involved for primary research and for verification/validation purposes. While major concerns have been raised on process/product qualification and current AM capabilities, the results show that there is a strong confidence on the disruptive potential of AM to be applied in front-end of DS2 systems to support “Complex Engineering Systems” in the future. While this paper provides only next-generation AM applications for RN, substantial conceptual development work has to be carried out to define an AM based system which is able to, firstly satisfy the “spares demands” of a platform and secondly is able to perform in critical environments such as at sea

Design of an empirical process model and algorithm for the Tungsten Inert Gas wire+arc additive manufacture of TI-6AL-4V components

In the wire+arc additive manufacture process parameters can be varied to achieve a wide range of deposit widths, as well as layer heights. Pulsed Tungsten Inert Gas was chosen as the deposition process. A working envelope was developed, which ensures unfeasible parameters combinations are excluded from the algorithm. Thanks to an extensive use of a statistically designed experiment, it was possible to produce process equations through linear regression, for both wall width and layer height. These equations are extremely useful for automating the process and reducing the buy-to-fly ratio. For a given layer height process parameters can be selected to achieve the required layer width while maximising productivity

Improved microstructure and increased mechanical properties of additive manufacture produced TI-6AL-4V by interpass cold rolling

Distortion, residual stress and mechanical property anisotropy are current challenges in additive manufacturing (AM) of Ti-6Al-4V. High-pressure, interpass rolling was applied to linear AM parts and resulted in a change from large columnar prior β grains to a completely equiaxed microstructure with grains as small as 89 μm. Moreover, α laths thickness was also reduced to 0:62 μm. The change in material microstructure resulted in a substantial improvement of all mechanical properties tested, which were also totally isotropic. In rolled specimens, maximum measured strength and elongation were 1078MPa and 14% respectively, both superior to the wrought material. Distortion was reduced to less than half. Rolling proved to be a relatively easy method to overcome some of the critical issues which keep AM from full industrial implementation

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

Optimization Under Uncertainty Using the Generalized Inverse Distribution Function

A framework for robust optimization under uncertainty based on the use of the generalized inverse distribution function (GIDF), also called quantile function, is here proposed. Compared to more classical approaches that rely on the usage of statistical moments as deterministic attributes that define the objectives of the optimization process, the inverse cumulative distribution function allows for the use of all the possible information available in the probabilistic domain. Furthermore, the use of a quantile based approach leads naturally to a multi-objective methodology which allows an a-posteriori selection of the candidate design based on risk/opportunity criteria defined by the designer. Finally, the error on the estimation of the objectives due to the resolution of the GIDF will be proven to be quantifiableComment: 20 pages, 25 figure

Analytical process model for wire + arc additive manufacturing

An analytical process model for predicting the layer height and wall width from the process parameters was developed for wire + arc additive manufacture of Ti-6Al-4V, which includes inter-pass temperature and material properties. Capillarity theory predicted that cylindrical deposits were produced where the wall width was less than 12 mm (radius <6 mm) due to the large value of the surface tension. Power was predicted with an accuracy of ±20% for a wide range of conditions for pulsed TIG and plasma deposition. Interesting differences in the power requirements were observed where a surface depression was produced with the plasma process due to differences in melting efficiency and/or convection effects. Finally, it was estimated the impact of controlling the workpiece temperature on the accuracy of the deposit geometry

Designing a WAAM based manufacturing system for defence applications

Current developments in “Wire+Arc Additive Manufacturing” (WAAM) have demonstrated the suitability of the technology for rapid, delocalized and flexible manufacturing. Providing a defence platform with the ability of on-board WAAM capability, would give the platform unique advantages such as improved availability of its systems and ability to recover its capability after being subject to shock. This paper aims to investigate WAAM technology and define a WAAM based manufacturing system for In-platform applications

A review of additive manufacturing technology and cost estimation techniques for the defence sector

“Additive Manufacturing” (AM) is a promising technology which will provide major advantages to Defence Support Service providers, given its ability of delocalised manufacturing near the point of use. The technology is gaining increasing interest due to its disruptive potential. AM groups together a wide range of different approaches which have the ability to convert a 3D file into a physical product by depositing layer upon layer of material. AM is still under development and considered an immature technology. This immaturity provides high level of uncertainty around key indicators such as time and cost. These indicators represent also key decision variables to evaluate AM and compare it with traditional manufacturing. This review paper represents an investigation of existing knowledge on AM and aims to present to the reader the various AM approaches with a detailed focus on the most applicable technologies to Defence Support Services. The paper is structured as follows, firstly the various technologies of AM and their economic aspects are presented, secondly the cost modelling techniques are investigated and finally a discussion is carried out. The contribution of this paper is to present to Defence Support Service stakeholders the various AM technologies and cost modelling techniques for measuring the product or service cost