Development of forced cooling technology using a DLC coating tool with a small through-hole and a communicating tube regarding the turning for difficult-to-machine material

In turning, the insert tip is continuously covered with chips and the temperature at the tool tip is very high. Especially when difficult-to-machine materials are used as work material, the temperature is above the melting point and the insert tip melts. Forced cooling of tools in turning is necessary. On the other hand, environmentally friendly turning is also necessary. Therefore, in this research, the forced cooling technology using a DLC coating insert with a small through-hole and a communicating tube regarding the turning for difficult-to-machine material was developed and evaluated. A connecting tube is a system in which the hole in the insert and the bottom of the assistant tank are connected by a tube, which allows the cooling medium contained in it to flow freely, so that the height of the cooling medium in the hole in the insert and the height of the cooling medium in the assistant tank behave equally due to gravity. The communicating tube was used for supplying the cooling fluid without no-energy, and the cooling fluid using the strong alkaline water with pH 12.5 was used for environmentally friendly. This strongly alkaline water has a significant cooling capacity equivalent to that of tap water and, moreover, does not corrode metals other than copper and aluminum. The small through-hole was machined for the cooling function on the insert tip. To reduce cutting heat, the inserts are coated with a DLC coating with a small low coefficient of friction. The proposed method was finally evaluated using the difficult-to-machine material Ti6Al4V for the workpiece in several experiments; temperature rise on the insert tip, tool life, surface roughness on the workpiece after the turning. In addition, the machining time, the running cost and the CO2 emission were also evaluated. It is concluded from the result that: (1) the proposed forced cooling technology was very effective for the turning of a difficult-to-machine material, (2) in the proposed method, it is important to maintain the tool tip temperature below 500°C, (3) the proposed method was superior in terms of the machining time and the running cost.