Combined effect of jet overlap and its gradual variation in abrasive waterjet milling of non-flat cavities on Aluminum 7075-T6 alloy

Abstract

Generation of various forms of non-flat surfaces in advanced engineering materials (AEMs) is required for realizing a variety of functionalities across aerospace, automotive, biomedical, and defence industries. The conventional manufacturing process comes with limitations, such as high tool wear, poor machinability, thermal damage, and increased costs. Although abrasive waterjet machining (AWJM) is apt in this context, generating near-net shape non-flat cavities pose significant challenges due to the stochastic nature of the high-velocity aggressive jet. On the other hand, the majority of the literature reported on AWJM is related to through-cutting; although some studies are reported on flat milled surfaces, the research on the generation of non-flat surfaces is very limited. Among the many approaches available for the generation of non-flat surfaces, changing the jet overlap is one of the unexplored areas due to its complexity in understanding the underlying physical phenomena. Considering the ease with which the jet overlap can be changed, this study investigates the combined effect of jet overlap and its gradual variation direction on the generation of non-flat cavities in aluminium 7075-T6 alloy. For this purpose, an attempt is made initially to understand the effect of jet overlap on the erosion behaviour through CFD simulations. Furthermore, the gradual variation in the direction of the jet overlap (GVJO) prediction model is developed that helps in selecting (i) the overlap percentage, and (ii) the gradual variation in the direction of jet overlap, for the desired non-flat cavities. Following this, the jet paths are generated for the jet overlap sequence predicted by the GVJO model, featuring gradual variations in (a) the descending jet overlap, and (b) the ascending jet overlap. The combined effect of the jet-overlapping sequence predicted by the GVJO model and its placement direction is analysed across ten case studies. Finally, the milling experimental results demonstrated that a gradual variation in jet overlap alters the depth according to the desired non-flat cavities. The non-flat cavities generated by the jet path with the overlap variation in the descending manner perform well with a mean root mean square error (RMSE) of 233 µm against its counterpart that comes with a mean RMSE of 426 µm. The jet path with an ascending jet overlap features less surface roughness compared to its counterpart, with a mean surface roughness of 16 μm. The effective milling of non-flat cavities clearly illustrates the significance of variation in jet overlap, its gradual variation in the jet path, and the GVJO prediction model. Ultimately, highlights the capabilities of AWJM for near-net-shape manufacturing of AEMs.