## 1 Introduction  
Currently, helical milling is positioned as a good alternative to conventional drilling. In fact, the aerospace industry characterized by being at the forefront of technology seems to have found in this strategy an ally to improve the performance of drilling operations. This fact is reflected in research programs such as \"Clean Sky\" founded by the European Union for Horizon 2020, whose objectives include the development of innovative technologies to reduce the environmental impact of air transport and improve the sustainability of current manufacturing processes, being of great interest for this machining strategy [1, 2]. In this context, the aerospace industry faces the challenge of digitizing production processes in factories using sensors and information systems to transform production processes and make them more efficient. The challenge of achieving industry 4.0 must include the added difficulty of the high qualities required of the elements and the use of difficult-to-machine material. This highlights the titanium alloy UNS R56400 commonly called Ti6 Al4V, which due to its excellent relationship between mechanical properties/weight, and corrosion resistance stands out from other materials. Many drilling techniques uses of cutting fluids to minimize the generations of typical hole defect, especially in this material. Cutting fluids have benefits such as lubrication and cooling of the machining process, reducing the coefficient of friction between the tool and the workpiece, and between the tool and the evacuated chip. In addition, they favour the evacuation of the heat in the cutting area, which contributes to removal of the generated chip and improves the tool life. However, the use of mineral-based cutting fluids, require special treatment once they have been used to eliminate the toxic component and comply with environmental legislation [3]. The use of cutting fluid can reach a cost overrun of 16% to the machining process [4]. For this reason, there is a worldline tendency to minimize or eliminate the use of traditional cutting fluid in machining operations, betting on techniques more committed to the environment. The current trend is to use dry or near-dry machining techniques for green manufacturing [5; 6; 7]. The use of helical milling to obtain holes brings many advantages that were discussed in [PERSON]'s review [8]. These include the flexibility that kinematics brings to the process, more efficiently chip removal, the use of external cooling, and the forces developed during machining in the axial axis are lower compared to conventional drilling, a relevant factor in the formation of burrs in metal alloys and delamination in composite materials [9; 10]. Different researchers have addressed a large part of the typical defectology of the hole associated with this process. For example, [PERSON] compares two helical milling strategies and one drilling strategy, concluding that the best precision is obtained with helical although the diameters are always lower due to the flexibility of the tool; however, he does not find significant improvements in terms of surface quality [11]. [PERSON] compares conventional drilling with helical milling and concludes that helical milling improves surface quality and fatigue resistance [12]. [PERSON] studied the helical milling of Ti/CFRP stacks, finding an oversizing of the hole in CFRP and a reduction in the case of titanium [13]. [PERSON] observe the tool wear and its impact on the quality of the holes, finding a high quality of the holes until the end of the tool life; however, the frontal wear has a great impact on the burr exit [14]. On the other hand, [PERSON] compares conventional drilling and helical milling, studying tool wear and concluding that the tool's life in helical milling is longer than in conventional drilling. In addition, it is found that helical milling produces compressive residual stresses [15].