Titanium is a versatile high-strength material with low density, high melting temperatures and high reactivity with cutting tool materials. It’s low thermal conductivity increases the temperatures at the cutting edge and causes rapid wear and plastic deformation. Further, due to the high reactivity, it also results in chemical interactions with the cutting tool, which is responsible for crater wear during machining.
Titanium also gets strain hard during machining, which causes notch wear at the depth of cut and at the same time, low modulus of elasticity apart from high strength at elevated temperatures, which make it unique for being used for high temperature applications like aeroplane parts. With its exceptionally high strength-to-weight ratio with good corrosive resistance, the metal has high hot hardness and wear-resistance. Compared to steel, it is just as strong but only 40 per cent of its weight ratio compares to steel, which is twice as strong as aluminium but only 60 per cent more in weight compared to aluminium.
Additionally, there are some other types of titanium materials like Ti-5-5-5-3, which is also known as the Russian titanium and it is 30 per cent stronger than Ti-6Al-4V and its machinability is 50 per cent compared to the normal Ti-6Al-4V, which makes it more challenging when compared to the normal titanium. Another version of the metal, which is the Ti-407, is the new material, which is 20 times easier to machine than Ti-6Al-4V.
Recommendations of machine for titanium machining
It is very important to use the right and strong machines for titanium. Some of the recommendations for good milling machines for titanium include very high torque in machines, which is required and may go as high as 300–1500 Nm. Further, low RPM and in most cases, 3000 RPM is enough because carbide cutting tool is being used with a low cutting speed of 45 -100 m/min. Internal coolant is also a must; the higher it is, the better.
Machining methods in titanium
The tool life plays a critical role during the machining of titanium, so there are some good machining methods, which should be used specially during roughing so as to get higher productivity and better tool life. Some of the machining strategies for titanium machining include:
Dynamic turning: It is important to understand while doing turning of Ti Alloys to use the right strategy and dynamic turning is one of them, which gives higher productivity and safe process during rough turning .One needs to pick the right software for this. For example, the short version is that we will avoid full engagement (Ae 100%) and pursue a constant engagement angle (<30°) and thus constant temperature and chip average. This will give the optimum control over tool pressure, tool wear and chip control.
Dynamic milling: This is an effective milling method for roughing with solid carbide tools and with indexable tools with higher cutting length. There is a strong tendency towards advanced roughing/dynamic milling optimised strategies based on algorithms. This has to be split into two main algorithm calculation directions. The first has to be the constant Vf constant arc of contact when entering concave convex area by adapting step over. The second has to be the variable Vf in order to maintain average chip thickness when entering concave convex area (arc of contact changes).
The key behind this is to use maximum depth of cut, which can be used according to application and smaller side step (Ae) so that one can achieve the highest metal removal rate (MRR). We also have the same time on the cutting edge where we use small depth of cut or higher. Further, it is very good once one has low torque in machines.
Helical milling: Helical milling is one of the best methods to scoop out material during roughing of titanium material especially when you have stronger machines, because it needs high torque.
Seco Tools pioneers in the machining of titanium material and is developing new technology of cutting tools, which are a cost-effective solution for such kind of materials.