# Wire Arc Additive and High-Temperature Subtractive Manufacturing of Ti-6 Al-4V
## 1 Introduction  
Additive manufacturing (AM), which enables rapid modeling of complex shapes, reduces manufacturing costs, and has high functionality, has recently received increased attention [1]. AM technology can create thin-layer 2D data from designed 3D CAD data, fabricate them in order, and acquire the 3D CAD data. It enables the quick creation of complex structures close to the final shape from 3D CAD data designed on a PC. If the design must be changed, it can be immediately remodeled. In this paper, we focused on wire and arc additive manufacturing (WAAM) using a plasma arc as a heat source and conducted the deposition and finishing processes with milling for Ti-6 Al-4V. Ti-6 Al-4V components are often used for aircraft parts due to their high specific strength and corrosion resistance [2, 3]. Ti-6 Al-4V components made by AM technology have a better yield rate than forged products, because they can be produced in near-net shapes. Cost reduction is expected by adopting parts created with AM technology. Ti-6 Al-4V is a difficult-to-cut material, and the amount of cutting can be significantly reduced by fabricating it into a near-net shape. Research on the AM of Ti-6 Al-4V is actively underway. Oxidation during the process is a challenge because titanium alloy will easily oxidize, which deteriorates the part's mechanical properties. [PERSON] et al. examined fabricating Ti-6 Al-4V using a chamber filled with argon gas [4]. The mechanical properties of the fabricated objects were altered due to the deposition path. Specim vertical to the deposition path has better elongation than horizontal specimens. \(\beta\) grains tend to grow in the direction vertical to the deposition path in objects fabricated by WAAM, which is considered to be one of the causes of the decrease in ductility in horizontal specimens. [PERSON] et al. fabricated Ti-6 Al-4V objects using a local shield, and investigated the effective amount of argon (Ar) gas needed and the position of the local shield [5]. They found that the oxygen (O\({}_{2}\)) concentration directly under the localshield tended to decrease as Ar gas supplied increased. [PERSON] et al. also fabricated Ti-6 Al-4V objects using a local shield to consider the mechanical properties and oxide layer thickness with and without the shield [6]. The elongation improved about 1% (from about 9 to 10%) by using a local shield. In addition, there was no significant difference between tensile strength and a 0.2% proof stress. The O\({}_{2}\) content of the fabricated object was reduced from 0.10 to 0.08% by the local shield, proving that fabricated objects with less oxidation could be obtained with the shield. Ti-6 Al-4V objects were fabricated by plasma welding, electron beam welding, and powder bed fusion (PBF), and the mechanical properties of the fabricated objects by tensile tests were examined [7; 8; 9]. Compared to the ASTM B381-13 value, tensile strength was higher, while elongation was about 3% lower than the ASTM standard. They also clarified that the mechanical properties of fabricated objects whose oxidation was suppressed using the local shield were not significantly different from those made by other methods. WAM components have irregularities on each layer, so they must be finished in order to serve as mechanical parts. Ti-6 Al-4V is a difficult-to-cut material due to its low thermal conductivity. A ceramic tool can be used for high-speed cutting, because it has high high-temperature strength. Ceramic tools include alumina-based ceramics [10; 11], silicon nitride-based ceramics [12; 13], cermet [14; 15], and salion-based ceramics [16; 17]. These applications have been reported. [PERSON] et al. performed high-speed milling of AM components using silicon nitride-based ceramic tools [12; 13]; a Ti-6 Al-4V workpiece made by direct metal laser sintering was grooved at room temperature. Experiments were conducted by changing the feed rate.