Abstract
Wire + Arc Additive Manufacturing (WAAM) is a technology potentially offering reduction of material wastage, costs and shorter lead-times. It is being considered as a technology that could replace conventional manufacturing processes of Ti-6Al-4V, such as machining from wrought or forged materials. However, WAAM Ti-6Al-4V is characterized by coarse β-grains, which can extend through several deposited layers resulting in strong texture and anisotropy. As a solution, inter-pass cold rolling has been proven to promote grain refinement, texture modification and improvement of material strength by plastically deforming the material between each deposited layer. Nevertheless, with the increased interest in the WAAM technology, the complexity and size of the deposited parts has increased, and its application can be hindered by the low speed and complex/costly equipment required to perform rolling at this scale. Therefore, Machine Hammer Peening (MHP) has been studied as an alternative cold work process. MHP can be used robotically, offering greater flexibility and speed, and it can be applied easily to any large-scale geometry. Similarly to rolling, MHP is applied between each deposited layer with the new ECOROLL peening machine and, consequently, it is possible to eliminate texturing and reduce the β-grains size from centimeters long to approximately 1 to 2 mm. This effect is studied for thin and thick walls and no considerable change in grain size is observed, proving the applicability of MHP to large components. The yield strength and ultimate tensile strength increases to 907 MPa and 993 MPa, respectively, while still having excellent ductility. This grain refinement may also improve fatigue life and induce a decrease in crack propagation rate. In this study, it has been shown that MHP is a suitable process for WAAM Ti-6Al-4V applications, can be applied robotically and the grain refinement induced by very small plastic deformations can increase mechanical properties.
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Acknowledgments
The authors would like to thank Alfred Ostertag, Marco Nischkowsky, Karsten Roettger and Stefan Zenk of ECOROLL AG for providing the ECOpeen-C MHP tool and for the operational support, as well as, to Flemming Nielsen, Nisar Shah and Steve Pope for the technical support throughout the experiments carried at the WELPC, Cranfield University. The authors gratefully acknowledge the funding received from the European Union’s Horizon 2020 research and innovation program in the project LASIMM (Large Additive Subtractive Integrated Modular Machine) under the grant agreement No 723600. The authors are also grateful for the funding of the Engineering and Physical Sciences Research Council (EPSRC) through New Wire Additive Manufacturing (grant number EP/R027218/1) and Open Architecture Additive Manufacturing (grant number 113164) research program.
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Neto, L., Williams, S., Ding, J., Hönnige, J., Martina, F. (2020). Mechanical Properties Enhancement of Additive Manufactured Ti-6Al-4V by Machine Hammer Peening. In: Itoh, S., Shukla, S. (eds) Advanced Surface Enhancement. INCASE 2019. Lecture Notes in Mechanical Engineering. Springer, Singapore. https://doi.org/10.1007/978-981-15-0054-1_13
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