Titanium machining is a growing industry. Everyone from aerospace and automotive, to medicine are demanding high strength parts with lower weights. Anyone working with titanium will have to take certain factors into consideration to get the most out of their time and money.
Titanium is often described as difficult to machine. This is somewhat of a misnomer, titanium is only difficult to machine if you are trying to work with it in the same way you would work with other metals such as steel. To avoid this pitfall, it is essential to understand the properties to titanium. If you account for things like titanium’s chemical reactivity and low heat conductivity, working with titanium becomes no different than machining other metals.
Titanium is a relatively safe metal to work with. It has an auto-ignition temperature of 2,200F in air so it is unlikely to ignite when milling with coolant. The use of coolants will also prevent the build-up of titanium dust in the air. This is of particular importance because the auto-ignition temperature of titanium dust in air is 450F. Dry titanium burns slowly and can be controlled with dry table salt or a type D fire extinguisher. Remember not to apply water to a titanium fire as it can cause an explosion. Contact with titanium also produces no toxic effects.
Titanium does not conduct heat well. This means that when using something like an end mill in a CNC machine, the titanium will not heat; instead, all of the energy generated by friction is stored in the cutting edge of the end mill. Titanium’s low thermal conductivity is due to the element’s relatively low number of delocalised electrons. That is the same reason it is a poor conductor of electricity. What this means is anyone working with titanium will have to use lower cutting speeds. Reducing the cutting speed lowers heat generation in your tooling. Remember, a 30% increase in speed can shorten tool life by as much as 80%. To make up for lower cutter speeds, you can increase the feed rate on your CNC machine. This will have little impact on tool temperature but will make up for the lower speed. To learn more about this you can visit our speeds and feeds page.
Tool heating can be further reduced by using a large flow of cutting fluid. It is very important to remember that the fluid needs to be directed precisely at the cutting point. Titanium’s low heat conductivity means the refrigeration effect is greatly reduced so you need plenty of coolant in just the right place.
Titanium is a highly reactive metal, it will burn in oxygen and nitrogen. At high temperatures it can also form micro welds and actually start to smear as it reacts with tooling. This damages the cutting surface of the tool and has potentially disastrous consequences for parts. If the titanium is smearing, it is actually being spread across the surface you are machining. This could hide or close up small cracks which may then be missed in a visual inspection. Small particles of titanium can also cause tool abrasion which can lead to uneven tool wear.
If you are struggling with high chemical reactivity, try varying the depths of your cuts to spread out the tool wear. To learn more about tool wear and other common issues, visit our common problems page.
While aircraft manufacturers and other industries appreciate the elastic qualities of titanium, this property poses some challenges when machining. Under tool pressure, titanium deflects which means the cutting edge slides along the material rather than removing titanium. This can cause serious chatter problems, damaging your titanium and generating a huge amount of heat, which can ruin tooling.
To lower chatter, make sure your entire system is stiffened. This includes your CNC machine, spindle, tool holder, and tool. To learn more about how to avoid ruining your titanium and increase tool life, please visit our waste reduction page.
Titanium can harden when worked, which significantly reduces the built up edge during machining. This can alter cutting angles leading to a thin chip that has a small contact area with the tool face. That increases the load over a section unit. The problem is exacerbated if your tooling is dull or your cutter has inappropriate geometry. This can lead to plastic deformation, which hardens the titanium. Once the titanium is work hardened, your CNC cutter’s speed will be incorrect and cause increased tool wear.
One way to prevent hardening is to never stop your tool feed during the machining process. This will instantly harden the titanium, heat the tool and cause breakage.
This can help you avoid work hardening and get the most out of your tooling.
During forging, titanium can develop stress which can affect the machining process. This is usually caused by severe deformation during forging and is most common in high strength materials like titanium grade 5. Heat treatments can be used to relieve stress but they must be applied before the machining processes begins.
Forged titanium can suffer as a result of high forge impact, low forge temperature and a poor element mix during the meeting of ingots. These can all cause stress or variation in the material, which can make machining more complex. Titanium also tends to return to its original shape, which can make machining thin walls difficult.
If you are interested in machining titanium, SGS Europe has an excellent line of end mills that can help improve productivity. We also offer 3 free regrinds for every bit we sell so you can be assured to get the best when you buy with us.
For more information titanium forgings, please get in touch with us!