Titanium and its alloys (Ti) are attractive for many applications due to their superior properties.However, they are regarded as hard-to-machine materials. Drilling is an important machining process since it is involved in nearly all Ti applications. It is desirable to develop cost-effective drilling processes for Ti and/or improve the cost-effectiveness of currently-available processes. Such development and improvement will be benefited by a comprehensive literature review of drilling processes for Ti. This paper presents a literature review on mechanical drilling processes for Ti, namely, twist drilling, vibration assisted twist drilling, ultrasonic machining, and rotary ultrasonic machining. It discusses cutting force, cutting temperature, tool wear and tool life, hole quality (diameter and cylindricity, surface roughness, and burr), and chip type when drilling of Ti using these processes.

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Unique properties of titanium alloys (such as high strength-to-weight ratio, heat and corrosion resistance, shock resistance and erosion resistance) make them important materials in industries. However, poor machinability poses considerable problems in fabrication of components from titanium alloys. Therefore, to machine titanium alloys cost effectively still remains a challenge. In this paper, Rotary Ultrasonic Machining (RUM) of titanium alloy (Ti-6Al-4V) has been investigated. Four tools with different specifications (diamond grit size, diamond concentration and metal bond type) are used to drill holes in titanium alloy workpieces. The cutting force, surface roughness on machined holes and rods and tool wear are compared.

Due to their unique properties, titanium alloys are attractive for some unique applications especially in the aerospace industry. However, it is very difficult to machine these materials cost-effectively. Although many conventional and non-conventional machining methods have been reported for machining them, no reports can be found in the literature on rotary ultrasonic machining of titanium alloys. This paper presents an experimental study on rotary ultrasonic machining of a titanium alloy. The tool wear, cutting force, and surface roughness when rotary ultrasonic machining of the titanium alloy have been investigated using different tool designs and machining conditions. The results are compared with those when machining the same material with diamond grinding.