Mechanical Engineering - Production Engineering - Discussion

Titanium and its alloys have gained widespread applications in aerospace, biomedical industries due to their following favourable properties: They are lightweight, possess high strength, have excellent fatigue performance and offer high resistance to an aggressive environment.

It is unfortunate that the above favourable properties in practical applications, prove to be a curse during machining:

Titanium alloys due to their high strength, low thermal conductivity and chemical reactivity with tool materials (at elevated temperatures), pose a hazard to the tool and significantly reduce the tool life.

In addition, a relatively low Young's modulus of titanium alloys leads to spring-back and chatter leading to the poor surface quality of the finished product.

Finally, during turning and drilling, long continuous chips are produced; causing their entanglement with the cutting tool and making automated machining near impossible.

The solution are;

Application of high-pressure coolant during cutting and drilling operations. This is quite expensive owing to coolant costs.

"Ultrasonic assisted machining" in which the tool is imparted an ultrasonic vibration with very low amplitude. Instead of continuous contact of the tool with work, this method offers an intermittent contact reducing the heat-affected zones at the chip-tool interface, work-flank interface etc. Thus increasing the tool life.

Machining titanium is challenging due to the following factors:

Chemical reaction: Titanium tends to react with the cutting tool material at high temperatures, leading to tool wear and reduced tool life.
Low thermal conductivity: Titanium has low thermal conductivity, which causes heat to concentrate at the cutting edge, further accelerating tool wear.
Low tool-chip contact area: The contact area is relatively small, which increases cutting forces and heat generation.

However, the primary reason in this context is the chemical reaction between the tool and the workpiece.

Titanium alloys due to their high strength, low thermal conductivity and chemical re-activity with tool materials (at elevated temperatures), pose a hazard to the tool and significantly reduce the tool life.

In addition, a relatively low Young\'s modulus of titanium alloys leads to spring-back and chatter leading to poor surface quality of the finished product.

Finally, during turning and drilling, long continuous chips are produced; causing their entanglement with the cutting tool and making automated machining near impossible.

B is correct answer.

Reference: MANUFACTURING ENGINEERING AND TECHNOLOGY SIXTH EDITION by Serope Kalpakjian.

"Titanium and its alloys have very poor thermal conductivity (the lowest of all
metals), causing a significant temperature rise and built-up edge. They are highly reactive and can be difficult to machine.".

Answer is None of these. Because the titanium has very high strength. Due to low thermal conductivity of material, the heat is not dissipated from the primary deformation zone and chips gets accumulated thereby decreasing the shear plane angle and cutting force increases. This question asked in ESE 1992.

Titanium is very reactive in nature that is why it's machining is very difficult and this is the reason why it has limited applications, titanium is light in weight and exhibit high strength. It's use is limited because it's usage is not economical e.g aircraft application.

Low modulus of elasticity tends it to move away from cutting tool easily. It makes it more springy and difficult to maintain proper contact with the tool.

Option given is one probable answer. And coming to reactivity, it satisfies both B and C.

Titanium alloys due to their high strength, low thermal conductivity and chemical reactivity with tool materials (at elevated temperatures), pose a hazard to the tool and significantly reduce the tool life.

Titanium alloys due to their high strength, low thermal conductivity and chemical reactivity with tool materials (at elevated temperatures), pose a hazard to the tool and significantly reduce the tool life.

The machinability of titanium alloys is difficult due to their low thermal conductivity and elastic modulus, high hardness at elevated temperature, and high chemical reactivity.