The Performance of Diamond-Like Carbon Coated Drills in Thermally Assisted Drilling of Ti-6Al-4V

Abstract

Drilling performances of diamond-like carbon coatings incorporating W (W-DLC) deposited on high-speed steel tools were evaluated when drilling TÍ-6AI-4V at 25 °C and under thermally assisted machining (TAM) conditions at 400°C. Di-y drilling using W-DLC coated drills caused immediate tool failure as a result of titanium adhesion. The tool lives improved for TAM drilling using W-DLC when the TÍ-6AI-4V was placed (with diy surface) in a cooling bath at -80°C and resulted in low and uniform drilling torques as well as good surface finish. The low coefficient of friction (COF) of W-DLC against Ti-6AI-4V observed under TAM conditions was attributed to the formation of W oxide layers at the tool surface, as determined by Raman spectroscopy. Introducing a cooling bath was necessary in order to restrict the temperature rise in the workpiece that caused rapid tool wear above 500 °C during drilling operations and also to prevent adhesion with minimal built-up edge (BUE) formation during drilling. The TAM performance of W-DLC coated drills was shown to be similar to that of WC-Co drills used in conventional flooded drilling.

Tool Life Study of Coated/Uncoated Carbide Inserts during Turning of Ti6Al4V

“…Nevertheless, it was reported that DLC coated tools did not out-perform the standard cutting tools used for conventional machining of hard materials [18]. Bhowmick and Alpas [19] noticed short tool life of the DLC coated carbide drills when drilling Ti-6Al-4V alloy in dry cutting condition, which was attributed to the strong adhesion of titanium to the cutting tool similar to the obervation made in this current study. However, when the same alloy was placed in a cooling bath at -80°C and thermally assisted drilling was performed at 400°C, a significantly prolonged tool life was achieved along with low drilling torque and good surface finish.…”

Effect of WS2 particles in cutting fluid on tribological behaviour of Ti–6Al–4V and on its machining performance

“…Another method consisted of using cryogenic cooling leading to shorter chip segments [12][13][14]. Thermally assisted machining was also suggested for the improvement of the machining performance of Ti alloys by reducing their yield strength [15,16]. Ultrasonic-assisted machining that promotes chip segmentation as a result of the application of vibrational amplitude to the tool [17,18] has also been utilized.…”

Comparison of Endmill Tool Coating Performance during Machining of Ti6Al4V Alloy

“…Similarly, in another study, it was reported that diamond-like carbon (DLC) coated carbide drills exhibited short tool life when drilling titanium without the use of coolants. However, when thermally assisted drilling was performed placing the workpiece in a cooling bath at -80°C, the tool life improved dramatically owing to the effective heat removal as well as reduced friction between the DLC coated drills and the chips evacuating from the flutes [12].…”