High Pressure Interpass Rolling of Wire + Arc Additively Manufactured Titanium Components

Abstract

Abstract. Wire + Arc Additively Manufactured components contain significant residual stresses that manifest in distortion. Each layer of an additively manufactured wall was rolled with the aim of reducing the residual stress. Neutron diffraction and contour method measurements show that the residual stresses were reduced -particularly at the boundary with the substrate. The process also reduced distortion, and refined the microstructure which may facilitate implementation on aerospace components. IntroductionAdditive manufacture describes a collection of manufacturing processes where components are manufactured by breaking a CAD model down into layers each of which are then deposited using a variety of techniques that are either powder or wire-based. One of those techniques, Wire + Arc Additive Manufacture (WAAM) [1] uses deposition processes based on welding to deposit metal in the form of wire. The process could have a significant and disruptive impact on manufacturing due to: reduced consumption of raw materials; reduced manufacturing costs and lead times; and increased design flexibility.WAAM is characterised by a number of issues that are slowing its wider implementation. The long, columnar grains in the microstructure of AM components leads to anisotropy [2]. Moreover, Ding et al. [3] describes how steel components are affected by residual stresses and distortion during WAAM. The distortion leads to poor build tolerances, while the residual stress negatively affects part performance. Recently, large residual stresses have been measured in titanium WAAM components by Hoye et al. [4]. Residual stresses have also been reported in parts manufactured by electron beam [5] and laser-based [6,7] additive manufacture processes.In the related field of welding, one way of counteracting the effect of differential thermal contraction is to induce a compensating plastic strain in the deposited region by mechanical means. Coules et al. [8] describes how high-pressure rolling can also induce the plastic strain required for relaxation of residual stress in welded joints. When carried out after welding, this method comprehensively changed the residual stress distribution, and produced large compressive stresses in the weld. A key advantage of rolling is that it can cause plastic deformation over the entire weld cross-section, rather than just at the surface which is often the case with peening techniques. This counteracts the residual stress caused by welding more effectively, and reduces distortion of the welded component as demonstrated by Wen et al. [9].In previous work [10] rolling was applied between passes (after cooling to room temperature) of WAAM deposited walls. Two different roller profiles were investigated: the first, called the "profiled" roller, used a grooved profile that matched the top surface of the WAAM deposit. The second, called the "slotted" roller used an additional 10 mm deep slot to constrain the lateral deformation of the deposited material. Distortion was significantly reduced and in the case of ...

Microstructure of Interpass Rolled Wire + Arc Additive Manufacturing Ti-6Al-4V Components

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Criticality of porosity defects on the fatigue performance of wire + arc additive manufactured titanium alloy

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Wire arc additive manufacturing of mild steel

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