# Evaluation of the Machinability of Ti-6 Al-4V Titanium Alloy by AWJM Using a Multipass Strategy
## 4 Conclusions  
The presented research was conducted to investigate the impact of the use of the multi-pass method on the geometric characteristics of slots produced in a Ti-6 Al-4V workpiece by AWJM, as well as the productivity and cutting performance variation, with respect to the number of passes. In order to conduct a comprehensive study, the effect of multiple passes was also evaluated on cases with different traverse feed rates and jet pressure values. After the experimental work was conducted and the results were properly analyzed, various conclusions were drawn.  
It was determined that the multipass strategy made it possible to generate deeper slots in the sample, without changing other machining parameters. Using the multipass method for machining Ti-6 Al-4V, the penetration depth was shown to have an almost linear dependence up to three passes in most cases. Jet pressure plays a significant role, as it can increase the depth considerably at higher values. Moreover, the anticipated correlation with jet pressure and traverse feed rate was also observed, due to the increased kinetic energy or decrease of the exposure time of the jet.  
Regarding the top kerf width, the findings confirmed that both of the other parameters and the multipass method did not have a large impact on the width of the slots under a constant abrasive mass flow rate and stand-off distance. The lack of a direct rule, according to which the kerf width varied, was noted, whereas for the highest number of passes, a slight increase of kerf width was observed in every case.  
The multipass method was confirmed to be a rather convenient and effective way to reduce the kerf taper angle. It was observed that, by increasing the jet pressure and number of passes, the kerf angle decreased. Due to the decreasing beam energy and the limitations of the method in reducing the angle, the influence of successive passes became smaller and smaller.  
Regarding MRR and cutting efficiency, it was shown that they are decreased with an increasing number of passes, thus it becomes evident that single-pass AWJM leads to a higher MRR and cutting efficiency compared to a multipass strategy in every case.  
From the obtained results, it becomes evident that in some cases, similar results can be obtained either by regulating crucial process parameters, such as jet pressure and traverse rate, or by using a different number of passes. In order to obtain both high productivity and favorable kerf characteristics, it is suggested that a value of jet pressure higher than 150 MPa, a moderate value of traverse feed, e.g., 500 mm/min, and a moderate number of passes are employed, as the use of a relatively high pressure and moderate traverse feed ensures a sufficient depth and MRR, and reduced kerf taper angle, whereas the use of two or three passes can maintain the top kerf width and kerf taper angle at acceptable levels without compromising the MRR.  
Conceptualization, N.E.K. and P.K.-O.; methodology, N.E.K., P.K.-O. and L.D.; software, L.D.; validation, N.E.K., P.K.-O. and L.D.; formal analysis, L.D.; investigation, L.D.; resources, P.K.-O. and L.D.; data curation, N.E.K. and L.D.; writing--original draft preparation, L.D., N.E.K. and P.K.-O.; writing--review and editing, A.P.M.; visualization, P.K.-O., N.E.K. and L.D.; supervision, A.P.M.; project administration, A.P.M.; funding acquisition, N.E.K. All authors have read and agreed to the published version of the manuscript.  
This research received no external funding.  
Not applicable.  
The data presented in this study are available on request from the corresponding author.  
The authors declare no conflict of interest.