# Evaluation of the Machinability of Ti-6 Al-4V Titanium Alloy by AWJM Using a Multipass Strategy
## 1 Introduction
[14] considered the abrasive water jet slot milling in a 7075-T651 aluminum sample and analysis of the pressure, abrasive mass flow rate, stand-off distance (SoD), and traverse feed rate influencing the kerf profile. The results showed that for machining deeper grooves, the stand-off distance and the traverse feed rate should be reduced and the jet pressure increased. On the other hand, for increasing the width of the cut, an increase of the stand-off distance is required. Since several studies have performed investigations of the material removable mechanism and improving the machining quality, researchers are trying to define the optimal cutting process parameters by applying different strategies, such as a multipass strategy and optimization techniques. [PERSON] et al. [15] defined two different strategies using multipass AWJM technology. In the first, the jet passes through the material at maximum depth, while the second utilizes changing process parameters to deepen material penetration of every pass until achieving the desired depth of the cut. The optimal cutting time for cutting AISI 304 stainless steel with both strategies was two passes, but to obtain a better kerf taper, the optimal cutting time changed to three passes. The deep-cutting strategy had better results regarding the surface quality and geometrical output. In general, a multipass strategy can improve both the roughness and kerf taper, as shown by [PERSON] et al. [16]. [PERSON] and [PERSON] [17] proposed the use of oscillation at the nozzle as well as a multipass strategy, in order to further increase the depth of cut in a single pass with the same machining time. [PERSON] et al. [18] performed tests with two machining passes with different directions, under different traverse rates and stand-off distance values, in order to reduce roughness. They concluded that increasing the SoD at the second pass improved the quality, but reducing the SoD improved the kerf taper. In a similar study, [PERSON] et al. [19] tested four different multipass strategies, such as machining in the opposite direction or using a reduced traverse speed. They revealed that an opposite secondary pass provided better results. [PERSON] et al. [20] introduced simulation and CAM generated tool path, in order to minimalize undesired deviations of the programmed feed rate, such as feed rate drops at sharp corners. Experiments on cutting carbon fiber-reinforced plastics using multipass AWJM were conducted by [PERSON] et al. [21], as a method that increases surface quality. Their work enabled the reduction of kerf taper by 53% and the improvement of efficiency by 13%. Regarding the surface quality in the smooth cutting zone (SCZ), the former did not show any advantage over the latter, unless a highly increased pressure was employed for the second-pass cutting. It was also found from the experimental results that arranging a low traverse speed in the first-pass cutting was superior to using it in the second-pass cutting. In another work, [PERSON] et al. [22] examined the fatigue behavior of carbon/epoxy composites after using a controlled depth abrasive water jet milling method. A new parameter named \"crater volume (Cv)\" was defined as a proposition for quantifying and qualifying the machining quality in terms of induced damage, and the result confirmed that the new parameter was a more realistic indicator in the case of CFRP composites. [PERSON], [PERSON], and [PERSON] [23] considered the machining of a biomedical implant surface pattern on stainless steel 304 using controlled deposition of AWJM. The use of a multicriteria technique for creating this particular pattern was enabled. Multipass methods can be used for the waterjet technique, not only for cutting the material but can also find other applications. [PERSON] et al. [24] implemented a multipass method for an experiment in which the team analyzed the feasibility of using plain water jet cleaning in the paint removal process.