Highly Accurate Hole Making Technology of Ti6Al4V by Orbital Drilling: Effect of Oil Mist

Ti6Al4V, which is one of difficult-to-cut metals, is widely used in an aircraft structure, parts of a gas turbine and medical equipment, and hole making operation of Ti6Al4V is needed to fasten the parts. When a conventional drilling by twist drill is applied to hole making of Ti6Al4V, it is very difficult to obtain highly accurate hole in diameter, roundness and inlet - outlet edge quality due to a cutting temperature increase caused by a small heat conductivity of Ti6Al4V.Recently, it is well-known that Orbital drilling, which is also called Circular milling, Planetary drilling or Spiral drilling, is superior to conventional drilling for hole making of Ti6Al4V. The author newly developed a hole making machine to enable orbital motion based on Double Eccentric Mechanism so that an endmill driven by one built-in AC motor can rotate clockwise on its own axis at high speed, simultaneously can revolve counter-clockwise on eccentric axis at low speed (Yagishita, 2015).This paper deals with highly accurate hole making technology of Ti6Al4V by employing the machine and a new type cemented carbide endmill having 6 blades. By supplying oil mist from the tip of endmill using a hole through spindle, it is ascertained that cooling by oil mist is strongly effective in order to improve the deviation of hole diameter and roundness, and also edge quality at inlet and outlet of hole.