New observations on tool life, cutting forces and chip morphology in cryogenic machining Ti-6Al-4V

The use of cryogenic coolant in metal cutting has received renewed recent attention because liquid nitrogen is a safe, clean, non-toxic coolant that requires no expensive disposal and can substantially improve tool life. This work investigates the effectiveness of cryogenic coolant during turning of Ti-6Al-4V at a constant speed and material removal rate (125 m/min, 48.5 cm3/min) with different combinations of feed rate and depth of cut. It is found that the greatest improvement in tool life using cryogenic coolant occurs for conditions of high feed rate and low depth of cut combinations. However, this combination of machining parameters produces much shorter tool life compared to low feed rate and high depth of cut combinations. It is found that preventing heat generation during cutting is far more advantageous towards extending tool life rather than attempting to remove the heat with cryogenic coolant. Although cryogenic coolant is effective in extracting heat from the cutting zone, it is proposed that cryogenic coolant may limit the frictional heat generated during cutting and limit heat transfer to the tool by reducing the tool–chip contact length. The effect of cryogenic coolant on cutting forces and chip morphology is also examined.